Sawyer and Taylor (1949) observed that shell disease
produced thickening or complete destruction of the chitinous
layer of the gill filaments. No living gill tissue was attacked,
but the authors postulated respiratory impairment as an important
consequence of the disease. The infection appeared to be
entirely external, confined to the exoskeleton; it did not invade
living tissue nor was it transmitted internally. Sawyer and
Taylor also reported the disease to be present on the Maine coast
as well as in Canada, and considered it a potential threat to the
lobster industry, in view of the ease of-transmission and the
observed mortalities of captive individuals. The method of
infection of lobsters was unknown; lodging of bacteria in pores
and ducts of the shell was proposed by Sawyer and Taylor as a
route of invasion.

Subsequent long-term studies (1983-1988) of shell disease in
lobsters from Massachusetts coastal waters by Estrella (1984 and
pers. commun., 1988" °) have disclosed lowér prevalences in
cooler, more exposed, deeper water sites, as compared to inshore
sampling locations in harbors or near sewage outfalls.

King crabs, Paralithodes camtschatica and P- platypus, from
the eastern North Pacific, are occasionally affected by "rust
disease," which seems to result from action of chitin-destroying
bacteria on the exoskeleton. Bright et al. (1960) described
observations of rust disease in landed catches of king crabs from
Rachemak Bay, Cook Inlet, Alaska, as well as experimental studies
of the bacteria involved. The disease was characterized by
progressive darkening and softening of the exoskeleton,
particularly on the ventral surfaces. Underlying living tissues
were unaffected. Natural infections reached 11% in larger older
crabs in 1957 but were much lower overall in 1958 and 1959.
Shell abrasions and injuries served as foci of the disease, which
developed experimentally within two weeks. The disease was not
carried over to the new exoskeleton after molting, but recently
shed crabs were highly susceptible because the new shell was
easily punctured or abraded. Chitin-destroying bacteria were
isolated from infected crabs and cultured organisms produced the

lestrella, B. T. Massachusetts Division of Marine Fisheries,
East Sandwich, Massachusetts.

2pata furnished from unpublished contract report, "King crab
investigations of Cook Inlet, Alaska," by Donald B. Bright, Floyd
E. Durham, and Jens W. Knudsen of the Allan Hancock Foundation,
University of Southern California, Los Angeles, to U.S. Bureau of
Commercial Fisheries Biological Laboratory, Auke Bay, Alaska,
June 1960. (Cited in Sindermann and Rosenfield (1967) with
Permission (dated 1969) of Laboratory Director, U.S. Bureau of
Commercial Fisheries Biological Laboratory, Auke Bay, Alaska.)

-14-


BAROSS, J. A. & P. A. TESTER. 1975. Incidence and etiology of
exoskeleton erosion in the spider crab, Chionoecetes tanneri
Rathbun (Brachyura: Majidae). Soc. Invertebr. Pathol.,
Oregon State Univ., Corvallis, 3 pp. (Abstract).

BAROSS, J. A., P. A. TESTER & R. Y. MORITA. 1978. Incidence,
microscopy, and etiology of exoskeleton lesions in the
tanner crab, Chionoecetes tanneri. J. Fish. Res. Board Can.
35: 1141-1149.

BENTON, A. G. 1935. Chitinovorous bacteria. A preliminary
Survey. J. Bacteriol. 29: 449-463.

BIAN, B. Z. & S. EGUSA. 1981. Histopathology of black gill
disease caused by Fusarium solani (Martius) infection in the

Kuruma prawn, Penaeus japonicus Bate. J. Fish Dis. 4: 195-
201.

BODAMMER, J. E. & T. K. SAWYER. 1981. Aufwuchs protozoa and
bacteria on the gills of the rock crab, Cancer irroratus
Say: a survey by light and electron microscopy. J.
Protozool. 28: 35-46.

BOGDANOVA, E. A. 1957. Concerning Brandt's spotted diseases in
Ponto-Caspian Amphipoda and Mysidae, pp. 331-333. In
Petrushevskii, G. K. (Ed.), Parasites and Diseases of
Fish. Bull. All-Union Sci. Res. Inst. Freshw. Fish XLII,
Leningrad.

BURNS, C. D., M. E. BERRIGAN & G. E. HENDERSON. 1979. Fusa
sp. infections in the freshwater prawn Macrobrac
rosenbergii (De Man). Aquaculture 16: 193-198.

CAMPILLO, A. 1976. Etude des lesions d'origine bacteriennes de
la cuticle chez Palaemon serratus. Cons. Int. Explor. Mer,
C.M.1976/K:15, 4 pp.

CAMPILLO, A. & G. DEROUX. 1974.  Ascophrys rodor, n.g., n.Sp.,
un nouveau mode de parasitisme externe, aux dépens des
arthropodes, chez les ciliés: l'utilisation directe des
Strates cuticulaires du test. C. R. Acad. Sci. Paris, Ser.
D, 279: 1447-1450.

CIPRIANI, G. R., R. S. WHEELER & R. RK. SIZEMORE. 1980.
Characterization of brown spot disease of Gulf coast
shrimp. J. Invertebr. Pathol. 36: 255-263.

COOK, D. W. & S. R. LOFTON. 1973. Chitinoclastic bacteria
associated with shell disease in Penaeus shrimp and the blue
crab. J. Wildl. Dis. 9: 154-159.



%

en eae

To reinforce these findings of potential or actual tissue
invasion, an aberrant form of sheli disease in snow crabs,
Chionoecetes bairdi, from the North Pacific, caused by the
ascomycete fungus Trichomaris invadens, has been shown recently
to be a severe pathogen. Formerly thought to be only a cause of
exoskeletal erosion (Van Hyning and Scarborough, 1973), the
fungus was subsequently found to invade epithelial, connective,
and other tissues of the host (Hibbits et al., 1981). Such
invasion was thought to Prevent molting and to cause mortalities
(Sparks, 1982). There is a suggestion in these reports that at
least some of the fungi involved in shell disease may also be
capable of invading and destroying living tissue as well.

The statement by Alderman (1987) about the deposition below
shell lesions of brown nodules of melanized wound-reaction tissue
indicates a form of host response to destruction of the
integument, and Suggests an active process to contain the
invading microorganisms. It is interesting that an earlier
publication on shell lesions in lobsters from the New York Bight
(Young and Pearce, 1975) described host responses in the form of
cellular clots in the eroded pits of the exoskeleton. A similar
response was described in penaeid shrimp exposed to experimental
infection with chitinoclastic Vibrio spp. (Pylant and Leong,
1978). Their study disclosed a three-phase reaction:

(1) An attempt by the traumatized animal to slough the old
integument;

(2) Migration of hemocytes to the site of infection, where
they form a melanized defensive clot or plug,
Presumably to prevent further infection; and

(3) Deposition of chitin to the already existing
exoskeleton, possibly in a further attempt to protect
underlying tissues against bacterial infection.

More studies of host responses to shell disease, particularly
among the larger Crustacea, should contribute to full

understanding of the disease Process (see, for example, Johnson,
1976).

The shell disease syndrome has been observed in many
freshwater and marine species of Crustacea and under many
conditions, both natural and artificial. Actual shell erosion
seems to involve activity of chitinoclastic bacteria and fungi,
Sometimes with subsequent secondary infection of underlying
tissue by other facultative pathogens. Initial preparation of
the exoskeletal substrate by mechanical, chemical, or microbial
action probably is significant; thus high bacterial populations
and the presence of contaminant chemicals in polluted
environments, as well as extensive detrital and epibiotic fouling
of gills, could combine to make the disease syndrome a common
Phenomenon and a significant Mortality factor in crustaceans
inhabiting degraded environments.

-31-



MEIXNER, R. 1969b. y Is there a spot disease in Crangon
crangon? Int. Counc. Explor. Sea., Shellfish and Benthos
Comm., C.M./K:15, 3 pp.

MURCHELANO, R. A. 1982. Some pollution-associated diseases and
abnormalities of marine fishes and  shellfishes: a
perspective for the New York Bight, pp. 327-346. In Mayer,
G. F. (Ed.), Ecological Stress and the New York Bight:
Science and Management. Estuar. Res. Fed., Columbia, South
Carolina.

NIMMO, D. R., D. V. LIGHTNER & L. H. BAHNER. 1977. Effects of
cadmium on the shrimps, Penaeus duorarum, Palaemonetes pugio
and Palaemonetes vulgaris, pp. 131-183. In Vernberg, F. J.,
A. Calabrese, F. P. Thurberg & W. B. Vernberg (Eds.),
Physiological Responses of Marine Biota to Pollutants.
Academic Press, New York.

OVERSTREET, R. M. 1978. Marine Maladies? Worms, Germs, and
Other Symbionts from the Northern Gulf of Mexico. Miss.-
Ala. Sea Grant Consortium, Publ. MASGP-78-021, 140 pp.

OVERSTREET, R. M. & D. W. COOK. 1972. An underexploited Gulf
coast fishery: soft shelled crabbing. Am. Fish Farm. 3(9):
12-17.

PEARCE, J. B. (ED.). 1971. The effects of waste disposal in the
New York Bight--final report (draft) for 9 July 1971 to
Coastal Engineering Research Center, U.S. Corps of
Engineers, Washington, D.C. Prepared by Sandy Hook Sport
Fish. Mar. Lab., Sandy Hook, New Jersey.

PEARCE, J. B. 1972. <The effects of solid waste disposal on
benthic communities in the New York Bight, pp. 404-411. In
Ruivo, M. (Ed.), Marine Pollution and Sea Life. Fish. News
Ltd., London.

PYLANT, R. & J. K. LEONG. 1978. Experimental studies on brown
spot disease: etiology and histopathology. Proc. Soc.
Invertebr. Pathol. Reg. Worksh., Athens, Georgia.
(Abstract).

RINALDO, R. G. & P. YEVICH. 1974. Black spot gill syndrome of
the northern. shrimp Pandalus - borealis. dg. Invertebr.
Pathol. 24: 224-233. : TM .

ROALD, S. O., J. AURSJG & T. HASTEIN. 1981. Occurrence of shell
disease in lobsters, Homarusgammarus (L.), in the southern
part of the Oslo -Fjord, Norway. - Fisk. Dir. Skr. Ser.
Havunders. 17: 153-160. 27



Table 2 (continued).

Geographic Common name Pathogens
Host location of disease isolated References
King crab Eastern Rust disease Chitino- Bright et
(Paralithodes North elastic al., 19602
camtschatica) Pacific on bacteria
and blue a
king crab
(Paralithodes
platypus)
Tanner crab Oregon Shell disease Photo- Baross &
(Chionoecetes coast bacterium Tester,
tanneri) (deep water) sp. 1975;
TT Baross et
al., 1978
Red crab Submarine . Not Young,
(Geryon canyons of reported 1988
quinguedens) New York
Bight
Pacific crab California Exoskeletal Not Mearns,
(Mursia coast lesions reported 1973
gaudichaudii) resembling
"burn spot
disease" of
S European”
"crabs
Dungeness crab Yaquina Bay, Exoskeletal Vibrio Baross et
(Cancer Oregon lesions anguillarum al., 1978
magister )
SHRIMP
European brown Germany Black spot Not Meixner,
shrimp disease reported 1969a, b
(Crangon
crangon)
. U.K. Black necrosis Not Schlotfeldt,
reported 1972;
Abbott,
1977



Fig. 3. Advanced bacterial shell disease lesion in a penaeid

shrimp. (Photograph provided by D. V. Lightner, University
of Arizona, Tucson, Arizona.)

-18-



94

coucH, J. A. 1977. Ultrastructural study of lesions in gills of
a marine shrimp exposed to cadmium. J. Invertebr. Pathol.
29: 257-288.

COUCH, J. A. 1978. Diseases, parasites, and toxic responses of
commercial penaeid shrimps of the Gulf of Mexico and South
Atlantic coasts of North America. Fish. Bull. 76: 1-44.

DENNELL, R. 1947. The occurrence and significance of phenolic
hardening in the newly formed cuticle of Crustacea
Decapoda. Proc. R. Soc. (Lond.) B(Biol. Sci.)134: 485-503.

DENNELL, R. 1960. Integument and exoskeleton, pp. 449-472. In

Waterman, T. H. (Ed.), The Physiology of Crustacea, Vol. I.
Academic Press, New York.

DOUGHTIE, D. G. & K. RAO. 1983a. Ultrastructural and
histological study of degenerative changes leading to black
gills in grass shrimp exposed to a dithiocarbamate
biocide. J. Invertebr. Pathol. 41: 33-50.

DOUGETIE, D. G. & kK. RAO. 1983b. Ultrastructural and
histological study of degenerative changes in the antennal
glands, hepatopancreas, and midgut of grass shrimp exposed
to two dithiocarbamate biocides. J. Invertebr. Pathol. 41:
281-300.

EGUSA, S. & T. UEDA. 1972. A Fusarium Sp. associated with black
gill disease of the Kuruma prawn, Penaeus japonicus Bate.
Bull. Jpn. Soc. Sci. Fish. 38: 1253-1260.

EL-GAMAL, A. A., D. J. ALDERMAN, C. J. RODGERS, J. L. POLGLASE &
D. MACINTOSH. 1986. A scanning electron microscope study
of oxolinic acid treatment of burn spot lesions of
Macrobrachium rosenbergii. Aquaculture 52: 157-171.

ESTRELLA, B. T. 1984. Black gill and shell disease in American
lobster (Homarus americanus) as indicators of pollution in
Massachusetts Bay and Buzzards Bay, Massachusetts. Mass.
Dept. Fish. Wildl. Rec. Veh., Div. Mar. Fish. Publ. No.
14049-19-125-5-85-C.R., 17 pp.

FISHER, W. S. 1977. Shell disease of lobsters, pp. 158-162. in
Sindermann, C. J. (Ed.), Disease Diagnosis and Control in
North American Marine Aquaculture. Elsevier Sci. Publ.,
Amsterdam.

FISHER, W. S., T. R. ROSEMARK & E. H. NILSON. 1976. The
susceptibility of cultured American lobsters to a
chitinolytic bacterium. Proc. World Maricult. Soc. 7: 5ll-
520.

-36-



ABSTRACT

The shell disease syndrome has been reported from many
freshwater and marine crustaceans of economic importance. Signs
of the disease syndrome include erosion and pitting of the
exoskeleton, resulting from activities of chitin-destroying
microorganisms--bacteria and fungi of several genera. Infection
is usually limited to the exoskeleton, although underlying living

tissues may be invaded by other opportunistic microbial
pathogens.

Shell disease is usually relatively rare in natural
populations, although a few epizootics have been reported. High
prevalences occur in captive populations, especially in
overcrowded holding facilities, probably because of greater
likelihood of damage to the cuticle and the presence of other
abnormal environmental conditions, including organic loading with
consequent high bacterial populations.

Mortalities from shell disease have been observed,
occasionally at high levels, in impounded populations.
Destruction of gills and adhesions of the exoskeleton which
prevent ecdysis have been considered to be responsible factors,
as have secondary systemic infections which develop after
perforation of the chitinous integument.

Shell disease has been observed in crustaceans from badly
degraded coastal/estuarine waters, often associated with so-
called "black gill" syndrome. Exoskeletal erosions are common in
lobsters, crabs, and smaller crustaceans from areas where
contaminated sediments occur, and the shell disease syndrome has
been produced experimentally by exposure of normal animals to
sediments from sewage sludge and dredge spoil disposal sites.
Organic loading in degraded waters, with consequent increases in
populations of heterotrophic bacteria--some of which may be
facultatively pathogenic--may be a significant factor.

Shell erosion in Crustacea is, therefore, a particular
problem in impoundments, in aquaculture facilities, and in

degraded habitats. It is contagious, but its etiology is
complex, involving chitinoclastic and other microorganisms and
environmental stressors. It may contribute to mortality,

principally by providing a route of entry for other facultative
pathogens, but also by destroying the gills of crustacean hosts
and by interfering with molting.

-iii-



Mortalities due to the shell disease syndrome have been
reported. In lobsters, death may be the consequence of
progressive erosion and destruction of gill membranes with
resultant reduced oxygen uptake, especially in hypoxic situations
(near sewage sludge dumpsites, for example). In shrimp, failure
to complete ecdysis because of shell adhesions has been
identified as a causal factor. In these and other species, death
may also result from secondary infections, after the exoskeletal
barrier has been breached, especially in the presence of high
populations of facultative pathogens. Additionally, it is quite
likely that severely affected animals would be more vulnerable to
predators.

Among the larger economically important Crustacea, shell
disease has been found to be more prevalent in older individuals,
that molt infrequently or not at all--since the exoskeleton would
be available for longer periods to the activity of chitin-
destroying microorganisms, and since the likelihood of minor
damage (which provides entry routes for such microorganisms)
would be increased. In some heavily exploited populations, shell
disease prevalences may have an inverse relationship to fishing
mortality. An intensive fishery (aS exists, for example, fer
lobsters and king crabs) removes more of the larger, slower
growing, more heavily diseased individuals from the fished
stocks, resulting in reduced prevalences, This relationship was
first suggested by Bright et al. (1960)“ for king crabs of the
North Pacific, and has been supported by findings of Ayres and
Edwards (1982), who sampled a developing fishery for European
edible crabs (Cancer pagurus) off the southwest coast of
Ireland. Rejection rates in newly exploited areas, because of
shell disease, were between 5 and 7%, and most of the crabs
rejected were larger older animals which had not molted for some
time. In other areas, which had been exploited for longer
periods of time, rejection rates because of shell disease were
usually less than 1%, and few younger crabs with advanced lesions
were observed. Advanced shell disease in younger animals may be
an indication of abnormal environmental conditions or nutritional
deficiencies--such as those which may prevail in aquaculture
facilities. Additional support for the observation that shell
disease is more prevalent in larger older individuals has been
provided by Estrella (pers. commun., October 1988°) from results
of a five-year Survey of lobster populations off the
Massachusetts coast. So, in natural habitats and in unfished
populations the disease can be described as "an infirmity of
advancing age." However, in abnormal habitats--impoundments,
culture facilities, or polluted waters--shell disease can become
a stress-related condition resulting from impaired metabolism,
with effects on chitin synthesis and possibly other defense
mechanisms, which are not necessarily age-related.



disease experimentally in normal crabs. Similar bacteria were
also isolated from ‘seawater in Kachemak Bay. The authors
concluded that the disease would not affect the commercial
fishery seriously unless the catch of crabs was substantially
less than annual recruitment, since larger individuals, which do
not molt annually, were more frequently infected. Since that
early report by Bright et al., similar exoskeletal lesions have
also been observed with prevalences up to 76% in tanner crabs
(Chionoecetes tanneri) from deep water (500-2000 m) off the
Pacific Northwest (Oregon) coast of United States (Baross and
Tester, 1975; Baross et al., 1978). Chitinolytic bacteria,
Principally of the genus Photobacterium, were isolated from
lesions consistently, and were found to be Capable of digesting
chitin rapidly at low temperatures (below 10°C).

A condition known as "Brandfleckenkrankheit" or "burn spot
disease" occurs in European edible crabs, Cancer pagurus
(Schdperclaus, 1935; Gordon, 1966; Bakke, 1973; Ayres and
Edwards, 1982). Although it is thought by some to be of fungal
etiology, others believe that it may be due to chitinovorous
bacteria. Gross pathology consists of dark brown to black spots
with red margins on the carapace and appendages, Particularly the
chelipeds. The chitin in the center of the Spots becomes
friable, and may be destroyed, exposing the underlying tissues.
Gordon reported that in 1956 many diseased crabs from waters to
the southwest of England and from the North Sea reached the
market. A similar disease is known in European freshwater
crayfish and river crabs, from which three fungi have been
isolated and described (Mann and Pieplow, 1938; Mann, 1940).

Another exoskeletal disease condition, caused by chitin-
destroying microorganisms, was described from blue crabs,
Callinectes Sapidus, taken in Chesapeake Bay (Maryland) by Rosen
(1967, 1970). Chitinoclastic bacteria were isolated from
characteristic brown depressed areas of chitin destruction. The
disease was progressive and was evident in 3% of crabs
examined. It is important to note, however, that the crabs had
been crowded together in shedding tanks for an extended period.
Shell disease has also been seen in blye crabs from Galveston
Bay, Texas (Hopkins, pers. commun., 19687), from the Mississippi
eccast (Overstreet, 1978), from Biscayne Bay, Florida (Iversen and
Beardsley, 1976), from the South Carolina coast (Sandifer and
Eldridge, 1974), and from the Pamlico River, North Carolina
(Engel, pers. commun., 1988*) (Fig. 2). Studies of shell disease
in blue crabs from the Gulf of Mexico, reported by Cook and

3Hopkins, S. H. Texas A&M University, College Station, Texas.

4Engel, DB. OW. National Marine Pisheries Service, Beaufort
Laboratory, Beaufort, North Carolina.

-15-



Cultured larval and postlarval lobsters, as well as adults,
have been found to be susceptible to shell disease (Fisher et
al., 1976; Fisher, 1977). Recent studies have frequently
implicated chitinolytic Vibrio spp. as etiological agents of
shell disease of lobsters although pseudomonads and aeromonads
have also been isolated (Malloy, 1978). Mechanical damage to the
epicuticle of the shell was considered by some investigators to
be essential to invasion by chitinolytic organisms (Rosen, 1970;
Fisher et al., 1978), although other routes are possible, such as
synergistic activity of lipolytic, chitinolytic, and proteolytic
bacteria (Baross and Tester, 1975). Additionally, in one recent
study of shell disease in cultured Homarus gammarus in Europe, a
fungus, Fusarium solani, was implicated (Alderman, 1981).

It seems that in cultured crustacean populations, as well as
in other types of captive stocks, similar predisposing factors
exist which lead to shell disease. The stresses of an abnormal
environment, possible nutritional deficiencies, presence of
chitinolytic microorganisms in a contained grow-out habitat, and
high densities of animals, combine to produce conditions
favorable to development of this and other infectious diseases.

VI. THE SHELL DISEASE SYNDROME IN CRUSTACEANS
FROM DEGRADED HABITATS

The shell disease syndrome in crustaceans (also known as
"exoskeletal disease" or "shell erosion") has been associated
with badly degraded estuarine/coastal habitats in a number of
studies and review papers (Rosenfield, 1976; Murchelano, 1982).
The association is direct enough to consider the shell disease
syndrome in some ways as the invertebrate analogue of fin erosion
in fish (Sindermann, 1979).

Two studies of shell disease in lobsters--one of Homarus
gammarus in the Oslofjord (Roald et al., 1981) and the other of
BH. americanus in the New York Bight (Young and Pearce, 1975)--
have indicated possible association of shell disease with sewage
sludge dumpsites. In the Norwegian study, 8 of 68 lobsters (12%)
sampled in 1979 two miles from a former (1959-1975) sewage sludge
dumpsite were affected, but no samples were obtained from control
or reference sites. Chitinoclastic bacteria of the genera
Vibrio, Aeromonas, and Pseudomonas were isolated from shell
lesions, which occurred principally on the ventral sides of the
large chelae. The authors suggested, but did not demonstrate, an
association between sludge disposal and the disease. It is
interesting, though not necessarily relevant, that three crabs,
Cancer pagurus, with shell disease were found in unrelated
Sampling in the Oslofjord in 1972-1973 (Bakke, 1973).

-21-

“We Seaceeintiattaa ie. Lee Ske



2
5

Lofton (1973), disclosed the Presence of several genera of
chitinoclastic bacteria in the lesions. The disease was
reproduced experimentally by damaging the exoskeleton and

Swabbing with cultured microorganisms isolated from natural
infections.

In submarine canyons of the New York Bight, prevalences of
shell disease in red crabs, Geryon quinguedens, averaged a
surprising 90%, with 5 to 13% showing signs of advanced
infections (Young, 1988). Most of the severely diseased crabs
were found in the larger size ranges sampled.

Shell disease, often described as "brown spot disease," is
also known in penaeid shrimp from the Gulf of Mexico (Cook and
Lofton, 1973; Couch, 1978; Lightner, 1988a). Characterized by
brown to black eroded areas on the body, appendages, or gills
(Fig. 3), the shell lesions are Progressive, with white margins
and depressed centers. Disease effects may be eliminated at
molting, unless the underlying tissues have been damaged by
secondary infections, and resulting adhesions prevent withdrawal
from the old exoskeleton. The secondary infections may also
become systemic and fatal (Lightner, 1988a).

IV. THE SHELL DISEASE SYNDROME IN IMPOUNDED
CRUSTACEAN POPULATIONS

The shell disease syndrome clearly exerts its most severe

effects in impounded populations of crustaceans~~especially
lobsters and crabs. This is entirely logical since:

° The animals may have been damaged, even slightly,
during capture and transport; such damage can provide
an entry route for chitin-destroying microorganisms.

° The animals are usually overcrowded in most
impoundment facilities (live cars, tanks, and pounds),

Providing an excellent opportunity for transmission of
contagious diseases.

° Also, persistent territoriality and aggressive
behavior under such crowded conditions lead to
fighting and consequent damage to exoskeletons.

° Purthermore, water quality conditions (temperature,
oxygen, and ammonia levels in particular) may be less

than optimum, resulting in stress on the captive
animals.

-17-



%

There is a suggestion from the literature on shell disease
that chitin-destroying marine microorganisms may vary in ability
to invade and degrade the exoskeletons of crustaceans. Some
recent reports of shell disease in larger species such as
lobsters and crabs suggest rapid invasion, with destruction of
significant areas of the chitinous shell, while other reports
suggest a more dispersed, slower-acting, generalized erosion.
The difference can be seen most clearly in lobsters. Samples
from Maine and the maritime provinces may contain individuals in
which the shell is extensively but superficially eroded, creating
a rough pitted surface; some samples from the middle Atlantic
States, on the other hand, may exhibit large put often discrete
lesions, with loss of spines and disappearance of extensive
portions of the carapace overlying the gills or of the cuticle of
the chelae. These differences in activity and effects may be
related to geographic or other variability in the kinds and
numbers of chitinoclastic microorganisms present. Some may act
more aggressively than others, depending on their temperature
optima, their exoenzyme competencies, and probably on the nature
and condition of host defenses. Other factors, such as organic
loading of habitats, may also contribute to the differences seen.

Growth of chitinoclastic bacteria may vary with temperature,
salinity, and hydrostatic pressure--so, for example, some (such
as Vibrio parahaemolyticus) may prosper in estuarine waters and
some may not; some (such as Photobacterium sp.) may flourish in
deeper colder waters whereas others may not. Additionally,
seasonal population maxima have been reported foz some
chitinoclastic Vibrio species, coinciding with decline in
zooplankton populations (Kaneko and Colwell, 1978).

The pathogenic role of chitinolytic microorganisms has often
been described as limited to destruction of the exoskeleton and
not the underlying tissues (except to provide a portal of entry
to other microbial invaders). This invasive process should be
reexamined, particularly in light of reports on fungal shell
disease by Forster and Wickins (1972) and Alderman (1987)
indicating that some forms of the disease syndrome--at least
those in which fungi have been implicated--may involve invasion
of underlying living tissues. The earlier report by Forster and
Wickins mentioned the presence of fungal hyphae in the tissues,
and the recent report by Alderman described "erosive
lesions...penetrating deeply into underlying tissues" and noted
that "brown nodules of melanized wound-reaction tissue become
deposited below the lesions." It is not clear from Alderman's
report whether the penetrating lesions were caused by the fungal
pathogen or by secondary microbial invaders, but this is clearly
@ matter of concern.



of the shell disease syndrome—as was pointed out by Fisher et
al. (1978) and Stewart (1980, 1984). Such a multifactorial
etiology, and the probable existence of several forms of the
shell disease syndrome, invite extensive discussion of the
disease condition in various habitats. This approach will be
followed in the following sections.

III. THE SHELL DISEASE SYNDROME IN CRUSTACEANS
PROM NATURAL HABITATS

The shell disease syndrome occurs at low prevalences in
lobsters, crabs, and shrimp sampled from natural habitats,
although indications of occasional epizootics exist--principally
in early reports of the condition in lobsters on the North
American east coast.

"Shell disease" caused by chitinolytic bacteria was first
described in American lobsters, Homarus americanus. Hess (1937)
isolated chitin-degrading bacteria from live lobsters impounded
at Yarmouth, Nova Scotia, but collected from various parts of the
Canadian maritime provinces. This was the first report of
attacks by such microorganisms on living Crustacea. The disease
was characterized by a pitting and sculpturing of the exoskeleton
(Pig. 1); although it was first seen in impounded lobsters,
similar conditions were later observed in freshly caught lobsters
from several widely separated Canadian fishing grounds. Initial
lesions occurred on the walking legs, and were distinguished by
white outer margins, from which the bacteria were most readily
isolated. Hess found the disease to be relatively rare in
natural populations but noted severe shell erosion and weakening
of lobsters stored in pounds over the winter. Microorganisms
isolated were able to decompose Pure chitin in saline solution
containing no other nitrogen or carbon source. None of Hess’
isolates--nor, for that matter, isolates prepared in subsequent
work with lobsters--was reported to reproduce the disease
experimentally.

In later studies, significant mortalities of lobsters were
reported to accompany the shell disease; Taylor (1948, 1949)
found that 71% of ‘infected captive lobsters died from the
disease, but observed no correlation between mortality and
intensity of external shell erosion. Acquisition of the disease
by healthy lobsters placed in seawater tanks with infected
individuals indicated direct transmission. The disease developed
slowly, requiring at least three months before the advanced
stages were reached. Progress of chitin destruction was reported
to be directly temperature-dependent and new shell laid down
after molting was not affected, except by reinfection (McLeese
and Wilder, 1964; McLeese, 1965).

-12-



Table 1 (continued).

Me ee teh

Disease effects

(a) Physiological

(b) Mortality

Preventive measures

Treatment

Destruction of exoskeleton provides

route of invasion for
facultative pathogens. Dest
of gill filaments

respiratory competence.
adhesions may prevent ecdysis

other
ruction
reduces
Shell

Reported mortalities of impounded

lobsters and crabs have

been

attributed to gill damage, secondary

infections, or failure of ecd

Avoid overcrowding impounded

ysis

popu-

lations and limit duration of
impoundment. Provide adequate diet

to cultured populations,

Limit

densities in culture tanks, and
reduce other forms of stress (poor
water quality, hypoxia, temperature

extremes)

Oxolinic acid baths have been
ed to be a_ successful
Measure in freshwater prawn
(El-Gamal et al., 1986). FP
and oxytetracycline have

report~-
control
culture
uranace
been

reported to be effective for shell

disease control in penaeid
culture (Lightner, 1984)

shrimp



Fig.

5S. Gills of juvenile shrimp, Penaeus californiensis, with
severe black gill condition. (Photograph provided by D. V.
Lightner, University of Arizona, Tucson, Arizona.)



On the basis of these limited studies, it may be inferred
that high prevalences of exoskeletal erosions in Crustacea have
some association with degraded habitats, and particularly with
sewage sludge dumpsites, although the condition may be found in
samples from unpolluted sites as well. The inference suffers,
however, from inadequate data from reference sites.

The shell disease syndrome in crustaceans from polluted
habitats is intimately associated with another general disease
sign or syndrome~-the so-called “black gill syndrome,"
characterized by sediment accumulation between gill lamellae,
accompanied by darkening of filaments. Substrate is provided for
microbial growth, and the syndrome is further characterized by

chitin deterioration and gill tissue necrosis (Sawyer et al.,
1979).

A recent study of shell disease and black gill disease in
lobsters from Massachusetts waters showed similar trends for both
diseases, with highest prevalences (up to 50%) in samples from
the most polluted sites--particularly Boston Harbor and Buzzards
Bay (Estrella, 1984). Prevalences in more exposed, deeper water
sites were generally low (Cape Ann, Cape Cod Bay, outer Cape Cod,
and Eastern Shore). Mortalities were not observed, but
population impacts were postulated, based on increased

vulnerability to hypoxia of lobsters with fouled or necrotic
gills.

Black gill disease was also examined in rock crabs, Cancer
irroratus, from the Atlantic coast of North America (Sawyer,
1982; Bodammer and Sawyer, 1981; Sawyer et al., 1979, 1983,
1984). High prevalences were associated with sewage sludge
and/or dredge material dumping areas where environmental
degradation was worst. Prevalences of black gill disease were as
high as 30% in some samples from the New York Bight apex. The
etiology of the disease is clearly complex, but it involves the
presence of black silt between lamellae and the presence of
epibiotic and epicommensal fouling organisms. Foci of black
discoloration were found to be areas in which several adjacent
lamellae were dead and necrotic, with accompanying melanization
of gill tissue (Sawyer et al., 1983). An association of the
black gill condition with shell erosion was stated clearly by
Sawyer (1982): “Specimens with gills judged to be 100% black
often had external blackening and carapace erosion. Black gills
often were melanized extensively with necrosis of gill cuticle or
entire gill filaments."

It should be noted, though, that black gills may also be
prominent gross signs of systemic infections, nutritional
deficiencies, or the presence of toxic compounds in the
environment and in the tissues. Phagocytes, fixed and motile,
may form pigmented aggregates near the tips of gill filaments, as
the terminal step in removal of killed pathogens, dead cells, or
toxic chemicals, since these deposition areas will be lost at

ee ee



americanus

I. INTRODUCTION .

Probably the most common and most widespread microbially
induced disease condition in crustaceans is the presence of
various kinds of exoskeletal erosions, due to the action of
chitinoclastic bacteria and fungi. Microorganisms of this type
are ubiquitous in the sea and are also common in freshwater
(Benton, 1935; Zobell and Rittenberg, 1938; Hock, 1940, 1941;
Lear, 1963; Hood and Meyers, 1974); they usually degrade the
exoskeletons of dead animals, but some may affect living
individuals as well. Over 30 species of chitin-destroying
bacteria are known, of which half have been isolated from shells
of crustaceans.

It should be emphasized at the outset that "shell disease"
is really not a discrete disease entity, but instead can be best
described as a “disease Syndrome” (or a complex of disease
Syndromes) characterized b rogressive exoskeletel erosion
resulting from activity of chitinoclastic microorganisms--often
affecting stressed crustaceans, Or those with damaged
exoskeletons.

Exoskeletal erosions have a variety of common names,
including “shell disease" or “box burnt disease" in blue crabs,
Callinectes sapidus, "shell disease" in lobsters, Homarus
"rust disease" in king crabs, Paralithodes
camtschatica, "brown spot," "black spot,” or "burn spot" disease
in shrimp and prawns, “black spot" disease in the European edible
crab, Cancer pagurus, and “spot" disease in crayfish. The
original names given to the disease condition in European
Crustaceans were “Brandfleckenkrankheit" (Mann and Pieplow, 1938)
and “Happichische FleckenkrankheitTM (Sch&perclaus, 1954).

For purposes of this report, information on the shell
disease syndrome in marine crustaceans has been somewhat
artificially divided into the following categories:

° Etiology;

° The disease in crustaceans from natural habitats;
° The disease in impounded crustacean ulations;
° The disease in crustacean aquaculture; and =

° The disease in crustaceans from degraded habitats

These categories are obviously not mutually exclusive, since
distinctions between cultured and impounded populations May be
blurred, and since differences between natural and degraded
habitats may be matters of degree. Despite such shortcomings,
the five subdivisions seem logical, since insights can be gained
from separate considerations of each.

-1-



4

CONTENTS
I. Introduction. ...ceee sec e cece ccc ecee rece weceeeeeeee 1
II. Etiology of the shell disease syndrome..... 2
III. The shell disease syndrome in crustaceans from
Matural habitatS......seeee cree ewe ee renee ee eececeee 12
Iv. The shell disease syndrome in impounded crustacean
populations........... eee ee as ee. 17
Vv. The shell disease syndrome in crustacean
aquaculture........-.- nec c cece cece cece cece seen cceee 20
VI. The shell disease syndrome in crustaceans from
degraded habitats...... weer c ences cca c cn ceceneses 21
VII. Discussion and conclusions...
VIII. Acknowledgments........----ee0- sec e rece cece ceseeeee 33
References.....-.-- wc cee ewe ence er eee enee eeeeeee 34

-v-



i
i

Fig. 1. Shell disease of lobsters caused by chitin-destroying
bacteria.

-13-



Table 1. Summary of

information about the shell disease

Syndrome in marine crustaceans.

. Geographic distribution

Species affected

Etiological agents

Prevalences

: Temperature effects

Disease signs

Known from many parts of the world,
in crustacean populations from
natural habitats, impoundments,
aquaculture, and degraded habitats

Reported most frequently from larger
economically important species of
Crustacea (lobsters, crabs, shrimp)
but occurs in smaller species (such
as amphipods and mysids) as well
(Bogdanova, 1957)

Heterotrophic microorganisms-—
bacteria and fungi--which have the
ability to degrade chitin

Prevalences usually very low ( < 2%)
in natural populations; epizootic
levels (10-90%) seen in impounded or
cultured populations, or those from
sewage sludge dumpsites (possibly
other areas as well)

Not well documented, but a direct
relationship has been reported
(McLeese and Wilder, 1964;
Schlotfeldt, 1972)

Progressive erosion of exoskeleton,
often beginning as brown focal
lesions which increase in size and
destroy extensive areas. May be
accompanied in advanced cases by
secondary infections of underlying
living tissues



° Some of the animals may have shed recently, rendering
them more susceptible to the combined stresses of poor
water quality and overcrowding--at a time of extreme
physiological changes and high oxygen demand
associated with ecdysis.

° Additionally, facultatively pathogenic bacterial
populations, including chitinovorous-. forms, may
increase rapidly in holding facilities, thereby
Providing a high level of infection pressure on
already stressed animals.

All these factors, acting in concert, can result in high
incidences of shell disease in captive populations. The
aggressiveness of the chitinolytic microbial strains that
develop, the temperature optima for such development, the extent
of damage to the epicuticle, the degree of stress that the
abnormal environment imposes on the animals, and the duration of
impoundment--all can contribute to epizootic levels of shell
disease under conditions of captivity.

It should” be noted too that shell infections seen in
impoundments may have existed before capture, or they may have
been acquired subsequent to capture. The low prevalences of the
disease normally seen in natural populations suggest, however,
that most infections are acquired and develop after
impoundment. It is equally likely that bacteria with
chitinolytic capabilities are part of the normal microbial flora
present on the body surfaces of any crustacean, and as such may
be introduced into holding facilities with their hosts. It
should also be noted that mortality among impounded crustaceans
may be high, especially in recently molted individuals, for a
variety of reasons, only one of which is shell disease. For
example, a systemic bacterial. disease, "gaffkemia," caused by
Aerococcus viridans var. homari, is well known as a cause of mass
mortalities in captive lobster populations.

5it is interesting to note that shell disease of Nova Scotian
lobsters, first described half a century ago by Kess (1937) is
apparently still a problem in impoundments. In a recent (1988)
communication from B. T. Estrella, high levels of the disease
have been reported by Massachusetts lobster dealers in winter
imports from coastal impoundments in southwestern Nova Scotia.
Some possible factors contributing to high prevalences in those
impounded populations include elevated organic loads in poorly
flushed bays and coves, water temperatures higher ‘than those-of
deeper coastal waters, and prolonged holding under crowded
conditions.

2#19-

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The Shell Disease Syndrome

in Marine Crustaceans

2. |. : U.S. DEPARTMENT OF COMMERCE
.., National Oceanic and Atmospheric Administration
National Marine Fisheries Service i
Northeast Fisheries Center : - ° 4
:’ Woods Hole, Massachusetts

“February 1989

| REPRODUCED BY ran : .. . wR -
1 U.S. DEPARTMENT OF COMMERCE - : oa

‘| NATIONAL TECHNICAL INFORMATION SERVICE
] SPRINGFIELD, VA 22161



SAWYER, T. K., E. J. LEWIS, M. E. GALASSO, J. J. ZISKOWSKI, A. L.
PACHECO & S. W. GORSKI. 1985. Gill blackening and fouling
in the rock crab, Cancer irroratus, as an indicator of
coastal pollution, pp. 113-129. in Ketchum, B-, J. Capuzzo,
W. Burt, I. Duedall, B. Park & D. Kester (Eds.), Wastes in
the Ocean, Vol. 6. Near-Shore Waste Disposal. J. Wiley &
Sons, New York.

SAWYER, W. H., JR. & C. C. TAYLOR. 1949. The effect of shell
disease on the gills and chitin of the lobster (Homarus
americanus). Maine Dept. Sea Shore Fish. Res. Bull. 1: 1-
10.

SCHAPERCLAUS, Ww. 1935. Die Ursache des pestartigen
Krebssterbens. 2Z. Fisch. Hilfswiss. 33: 343-366.

SCHAPERCLAUS , WwW. 1954. Fischkrankheiten. Akademic-Verlag,
Berlin, 708 pp.

SCHLOTFELDT, H. J. 1972. Jahreszeitliche Abhdngigkeit der
"schwarzfleckenkrankheit" bei der Garnele, Crangon crangon
L. Ber. Dtsch. Wiss. Komm, Meeresforsch. 22: 397-399.

SINDERMANN, C. J. 1977. Black-spot disease of fresh-water
shrimps, pp. 82-84. In Sindermann, C. J. (Ed.), Disease
Diagnosis and Control in North American Marine
Aquaculture. Elsevier Sci. Publ., Amsterdam.

SINDERMANN, C. J. 1979. Pollution-associated diseases and
abnormalities of fish and shellfish: a review. FPish. Bull-
76: 717-749.

SINDERMANN, C. J. & A. ROSENFIELD. 1967. Principal diseases of
commercially important marine bivalve Mollusca and
Crustacea. Fish. Bull. 66: 335-385.

SOLANGI, M. A. & D. V. LIGHTNER. 1976. Cellular inflammatory
response of Penaeus aztecus and P. setiferus to the
pathogenic fungus, Fusarium sp., isolated from the
California brown shrimp, californiensis. J. Invertebr.
Pathol. 27: 77-86.

SORDI, M. 1958. Micosi dei Crostacei decapodi marini. Riv.
Parassitol. 19: 131-137.

SPARKS, A. K. 1982. Observations on the histopathology and
probable progression of the disease caused by Trichomaris
invadens, an invasive ascomycete, in the tanner crab,
Chionoecetes bairdi. J. Invertebr. Pathol. 40: 242-254.



Table 2 (continued).

Geographic Common name Pathogens
Host location of disease isolated References
European U.K. Fungal shell Fusarium Alderman,
lobster disease sp. 1987
(Somarus
gammarus)
. Italy . Fusarium Sordi,
(aquaria) (Raumularia 1958
branchialis),
(Fungi
Imperfecti)
. Norway Shell disease Vibrio, Roald et
Aeromonas, al., 1981
Pseudomonas
European U.K. Fungal shell (Fungi Alderman,
"crawfish" disease Imperfecti) 1973
(Palinurus
elephas)
Spiny Italy . Didymaria Sordi,
lobster palinuri 1958
(Palinurus (Fungi
vulgaris) Imperfecti)
" Irish Sea Burn spot (Fungi Alderman,
Imperfecti) 1971, 1976
Spiny Florida Shell disease Not Robinson &
lobster reported Dimitriou,
(Panulirus 1963
argus )
Spotted spiny Florida . Not Iversen &
lobster reported Beardsley,
(Panulirus 1976
guttatus)



Table 2.

Reported occurrenc::., of shell disease

in marine

= : crustaceans of economic importance.

Geographic Common name Pathogens
Host location of disease isolated References
' LOBSTERS
American Nova Scotia Sheil disease Presumptive Hess,
lobster vibrios 1937
(Homarus
americanus)
. Nova Scotia il Pseudomonas, Malloy,
Vibrio 1978
" Maine " Not Taylor,
reported 1948, 1949;
Sawyer &
Taylor,
1949
. Norway " Vibrio, Roald et
Aeromonas, al., 1981
Pseudomonas
. California . Not Fisher et
(culture reported al., 1976
facility)
: " New York . Not Pearce,
- Bight reported 1971;
® Young &
i Pearce,
. 1975
2
z " Massachusetts . Not Estrella,
z coast reported 1984



i
'
i
t

IVERSEN, E. S- & G. L. BEARDSLEY. 1976. Shell disease in
crustaceans indigenous to south Florida. Progr. Fish-Cult.
38(4): 195-196.

JOHNSON, P. T. 1976. Bacterial infection in the blue crab,
Callinectes sapidus: course of infection and
pistopathology. J. Invertebr. Pathol. 28: 25-36.

JOHNSON, P. T. 1983. Diseases caused by viruses, rickettsiae,
bacteria, and fungi, pp. 1-78. In Provenzano, A. J., Ure
(Ed.), The Biology of Crustacea. Vol. VI. Pathobiology.
Academic Press, New York.

KANEKO, T. & R. R.- COLWELL. 1973. Ecology of Vibrio
parahaemolyticus in Chesapeake Bay. J. Bacteriol. 113: 24-
32.

KANEKO, T. & R. R.- COLWELL. 1975. Adsorption of Vibrio

parahaemolyticus onto chitin and copepods. Appl. Microbiol.
29: 269-274.

LEAR, D. W., JR. 1963. Occurrence and significance of
chitinoclastic bacteria in pelagic waters and zooplankton,
pp. 594-610. In Oppenheimer, C. (Ed.), Symposium on Marine
Microbiology. “Thomas, Springfield, Illinois.

LIGHTNER, D. V. 1975. Some potentially serious disease problems
in the culture of penaeid shrimp in North America. Proc.
U.S.-Japan Nat. Resour. Prog., Symp. Aquacult. Dis.,

Tokyo. pp. 75-97.

LIGHTNER, D. V. 1981. Fungal diseases of marine Crustacea, pp.
451-484. In Davidson, E. W. (Ed.), Pathogenesis of
Invertebrate Microbial Diseases. Allanheld, Osmun, Totowa,
New Jersey.

LIGHTNER, D. V. 1984. Diseases of cultured penaeid shrimp, pp.
289-320. In McVey, J. P. (Ed.), Handbook of Mariculture.
I. Crustacean Aquaculture. CRC Press, Boca Raton, Florida.

LIGHTNER, D. V. 1988a. Bacterial shell (brown spot) disease of
penaeid shrimp, pp. 48-51. In Sindermann, C. J. & D. V.
Lightner (Eds.), Disease Diagnosis and Control in North
American Marine Aquaculture. Elsevier Sci. Publ.,
Amsterdam.

LIGHTNER, D. V. 1988b. Black gill syndrome of penaeid shrimp,
pp. 86-88, In Sindermann, C. J. & D. V. Lightner (Eds.),

Disease Diagnosis and Control in North American Marine
Aquaculture. Elsevier Sci. Publ., Amsterdam.

-38-

wn



Pig. 4. Juvenile cultivated shrimp, Penaeus stylirostris, with
conspicuous black gills. (Photograph provided by D. V.
Lightner, University of Arizona, Tucson, Arizona.)



STEWART, J. E. 1980. Diseases, pp. 301-342. In Cobb, J. S. &
B. F. Philipps (Eds.), The Biology and Management of
Lobsters. Academic Press, New York.

STEWART, J. E. 1984. Lobster diseases. Helgol. Meeresunters.
37: 243-254.

TAYLOR, C. C. 1948. Shell disease as a mortality factor in the
lobster (Homarus americanus). Maine Dept. Sea Shore Fish.
Fish Circ. 4: 1-8.

TAYLOR, C. C. 1949, A study of lobster shell disease with
observations and recommendations. Maine Dept. Sea Shore
Fish. Res. Bull. April 1949, 5 pp.

THOMAS, J. H. 1954. The oxygen uptake of the lobster (Homarus

vulgaris Edw.). J. Exp. Biol. 31: 228-251.

UNESTAM, T. 1973. Fungal diseases of Crustacea. Rev. Med. Vet.
Mycol. 8: 1-20.

VAN HYNING, J. M. & A. M. SCARBOROUGH. 1973. Identification of
fungal encrustation on the shell of the snow crab
(Chionoecetes bairdi). J. Fish. Res. Board Can. 30: 1738-
1739.

WEIS, J. S., R. COHEN & J. K. KWIATKOWSKI. 1987. Effects of
diflubenzuron on limb regeneration and molting in the
fiddler crab, Uca pugilator. Aquat. Toxicol. 10: 279-290.

YOUNG, J. S. 1973. A marine kill in New Jersey coastal
waters. Mar. Pollut. Bull. 4: 70.

YOUNG, J. S. & J. B. PEARCE. 1975. Shell disease in crabs and
lobsters from New York Bight. Mar. Pollut. Bull. 6: 101-
105.

YOUNG, R. F. 1988. Shell disease among red crab inhabiting
submarine canyons near the New York Bight. Draft rep.,
Waste Management Inst., State Univ. New York at Stony Brook,
16 pp. (Cited with permission of the Director, Waste
Management Inst.)

ZOBELL, C. E.j & R. RITTENBERG. 1938, The occurrence and
characteristics of chitinoclastic bacteria in the sea. J.
Bacteriol. 35: 275-287.

EUs S. GOVERNMENT PRINTING OFFICE: 1989==600-620

-43-



ecdysis (Figs. 4 and 5). The black gill condition has been
reported in feral, cultivated, and experimental shrimp infected
by bacterial and fungal pathogens, and from crustaceans exposed
experimentally to heavy metals, biocides, petroleum, petroleum
derivatives, and other contaminants (Egusa and Ueda, 1972;
Rinaldo and Yevich, 1974; Lightner et al., 1975, 1977, 1979;
Fontaine et al., 1975; Couch, 1977; Sindermann, 1977; Bian and
Egusa, 1981; Doughtie and Rao, 1983a, b; Lightner, 1988b). Thus,
the black gill syndrome is a common and nonspecific pathological
manifestation, with complex etiolcgy, and is not unique to
polluted habitats; in this sense it is similar to the shell
disease syndrome. A recent attempt was made to distinguish
between the "black gill syndrome," an exogenous gill
discoloration seen in crabs and lobsters, which seems related to
sewage sludge-contaminated habitats, and a "black spot" gill
condition, characterized by discrete localized foci of melanin
deposition, forming blackened nodules in filaments or lamellae in
response to disease or injury (Sawyer, 1982)--but a broad-scale
evaluative study of the black gill condition in Crustacea from
various environments is clearly needed.

It might be well at this point to emphasize that the "black
gill syndrome" seems to be part of an important hemocyte-mediated

defensive response of Crustacea to chemical or physical trauma,

or to pathogen invasion. It results in sequestering and
subsequent removal during ecdysis of toxic substances or
microbial invaders. It also results in truncated gill filaments,
with consequent reduction in gas and ion exchanges.

The essence of the black gill syndrome seems to be the
formation of apical cellular plugs consisting of hemocytes,
formed in response to gill trauma or systemic microbial
infection. Phagocytized material is aggregated in gill apices.
Gill blackening has been reported as a consequence of protozoan
and fungal infection (Couch, 1978; Lightner et al., 1975) and of
exposure to chemical contaminants (Couch, 1977; Nimmo et al.,
1977; Doughtie and Rao, 1983a, b). In one study (Doughtie and
Rao, 1983b), several defensive responses to toxin exposure were
proposed. Included were:

(1) Pormation of a hemocyte plug in the apices of gill
lamellae;

(2) Phagocytosis of cellular debris by circulating
granular hemocytes;

(3) Phagocytosis of cellular debris by fixed
hepatopancreatic cells;

(4) Encapsulation by circulating hemocytes of degenerated
tissues resulting from action of toxins;

-25-



The literature on shell disease in crustaceans is extensive
and is increasing; the first report dates back almost a century
(Happich, 1900). Only a portion--but I hope a representative
portion--of that literature has been summarized here (Tables 1
and 2). As can be seen in the "References" section, interest in
the shell disease syndrome has shown a remarkable spurt in the
past several years, principally because of reports of high
prevalences in crustaceans from North American and European
waters, In some instances, surveys were conducted in severely
polluted estuarine/coastal areas, and a possible relationship
between the disease condition and habitat degradation has been
suggested--especially in the news media. In other studies, high
prevalences have been found in feral and impounded populations.
This document is an attempt to summarize available infcrmation
about shell disease and to reach some conclusions about its
etiology, environmental requirements, distribution, and effects.

II. ETIOLOGY OF THE SHELL DISEASE SYNDROME

The exoskeleton or cuticle of crustaceans is made up of a
thin outer layer, the epicuticle, consisting of proteolipoidal
material, including polyphenols, covering three inner chitinous
layers--the exocuticle, which is pigmented and calcified, the
calcified endocuticle, and the noncalcified endocuticle (Dennell,
1947, 1960). Chemically, chitin is a polysaccharide structurally
similar to cellulose except that the repeating unit is derived
from acetylglucosamine instead of glucose. The outer cuticular
layer of the exoskeleton, the epicuticle; is biochemically inert,
and shell erosion can occur when this layer is breached by
abrasion, injury, or possibly enzymatic digestion, exposing the
underlying chitinous layers to adequate numbers of chitin-
destroying microorganisms (Stewart, 1980). Additionally,
microbial invasion may occur through hypodermal ducts or setal
Eores (Fisher et al., 1978).

Because of the lipoidal nature of the epicuticle,
microorganisms producing extracellular lipase may initiate
lesions, even in the absence of abrasions. In one series of
experiments, all microorganisms able to infect healthy nonabraded
animals were lipolytic (Cipriani et al., 1980). The authors
pointed out, however, that the exoenzymes chitinase and protease
would be important in subsequent lesion development.

A variety of microorganisgs has been identified from shell
lesions, and it is probable that at least several kinds of
bactéria and fungi may act independently, concurrently,
sequentially, or synergistically in destroying chitin. In
penaeid shrimp, for example, bacteria of the genera Vibrio,
Aeromonas, Spirillum, and Flavobacterium and fungi of the genera
Fusarium, Haliphthoros, and Atkinsiella have been isolated from
erosive lesions (Lightner, 1988a). Chitin-degrading organisms

-2-



Fig. 2. Shell disease in the blue crab--early lesions (above)
and advanced lesions (below). (Photographs supplied by R.

M. Overstreet, Gulf Coast Research Laboratory, Ocean
Springs, Mississippi).

-16-



Shell disease, then, represents a stage in the e@ynamic
relationship of one group of chitin synthesizing animals-—the
erustaceans--with chitin-utilizing microorganisms. An uneasy
balance is maintained by the metabolic processes associated with
new cuticle formation at ecdysis, and subsequent cuticular
maintenance and repair--and the growth, metabolism, and
reproduction.-of microbes capable of degrading chitin. The
balance may be disturbed by environmental changes that redice the
erustacean's capabilities (metabolic and defensive) to maintain
an intact cuticle, or that encourage multiplication of the
facultative heterotrophic microorganisms with chitinolytic
capacities. Such disturbances can lead to destructive changes in
the crustacean exoskeleton that are labeled “shell disease."

VIII. ACKNOWLEDGMENTS

A number of people provided very useful comments on several
drafts of this document--comments which contributed to a more
complete description of the shell disease syndrome. TI would like
to thank the following (listed alphabetically): R. A. Bullis, D.
W. Engel, 8. T. Estrella, L. Leibovitz, R. A. Murchelano, E. J.
Noga, J. B. Pearce, T. K. Sawyer, R. L. Swanson, and R. R. Young--
without necessarily implying their concurrence with any or all of
the statements made or conclusions reached.



i ao

REFERENCES

ABBOTT, O. J. 1977. Black necrosis in brown shrimp Crangon
crangon, pp. 12-20. In Nelson-Smith, A. & F. M. Bridges
(Eds.), Problems of A Small Estuary. Proc. Symp. Burry
Inlet (South Wales), Univ. Coll. Swansea Inst. Mar. Studies.

ALDERMAN, D. J. 1971. Shellfish diseases in the United Kingdom
1970-71. Int. Counc. Explor. Sea, C.M. 1971/K:19, 4 pp.

ALDERMAN, D. J. 1973. Fungal infection of crawfish (Palinurus
elephas) exoskeleton. Trans. Br. Mycol. Soc. 61: 595-597.

ALDERMAN, D. J. 1976. Fungal diseases of marine animals, pp.
223-260. In Jones, E. B. (Ed.), Recent Advances in Marine
Mycology. Elek, London.

ALDERMAN, D. J. 1981. Fusarium solani causing an exoskeletal
pathology in cultured lobsters, Homarus vulgaris. Trans.
Br. Mycol. Soc. 76: 25-27.

ALDERMAN, D. J. 1987. Fungal shell disease of crustaceans.
Int. Counc. Explor. Sea, Identif. Leafl. Dis. Parasites Fish
Shellfish, Leafl. No. 32, 4 pp.

AMBORSKI, R. L., G. LOPICCOLO, G. F. AMBORSKI & J. HUNER.
1875. A disease affecting the shell and soft tissues of
Louisiana crayfish Procambarus clarkii-. 2nd Int. Symp.
Freshw. Crayfish, Baton Rouge, Louisiana, pp. 299-316.

ANDERSON, J. I. W. & D. A. CONROY. 1968. The significance of
disease in preliminary attempts to raise Crustacea in sea
water. Bull. Off. Int. Epizoot. 69: 1239-1247.

AQUACOP. 1977. Observations on diseases of crustecean cultures
in Polynesia. Proc. World Maricult. Soc. 8: 635-703.

AUSTIN, B. & D. J. ALDERMAN. 1987. Bacterial shell disease of
crustaceans. Int. Counc. Explor. Sea, Identif. Leafl. Dis.
Parasites Fish Shellfish, Leafl. No. 31, i pp.

AYRES, P. & E. EDWARDS. 1982. Notes on the distribution of
“black spot" shell disease in crustacean fisheries. Chem.
Ecol. 1: 125-130.

BAKKE, T. A. 1973. Brannflekk-syke hos taskekxabber, Cancer
pagurus L., i Norge. Fauna 26: 141-143,

-34-


A much more extensive and more definitive study of shell
disease and its possible associatior with pollution in the New
York Bight was reported by Pearce (i971) and Young and Pearce
(1975). Lobsters (Homarus americanus) and rock crabs (Cancer

irroratus) from grossly polluted areas of the New York Bight apex

were found to be abnormal, with appendage and gill erosion a most
common sign. Exoskeletal erosion occurred principally on the
tips of the walking legs, ventral sides of chelipeds, exoskeletal
spines, gill lamellae, and around areas of exoskeletal
articulation where contaminated sediments could accumulate.
Gills of crabs and lobsters sampled at the dumpsites were usually
clogged with detritus, possessed a dark brown coating, contained
localized thickenings, and displayed areas of erosion and
necrosis. Similar disease signs were produced experimentally in
animals held for six weeks in aquaria containing sediments from
sewage sludge or contaminated dredge spoil disposal sites.
Initial discrete areas of erosion became confluent, covering
large areas of the exoskeleton, and often parts of appendages
were lost. The chitinous covering of the gill filaments yas also
eroded, and often the underlying tissues became necrotic.

Dead and moribund crabs and lobsters have been reported on
several occasions by divers in the New York Bight apex, and
dissolved oxygen concentrations near the bottom during the summer
often approach zero (Pearce, 1972; Young, 1973). Low oxygen
stress, when combined with gill fouling, erosion, and necrosis,
could readily lead to mortality (Thomas, 1954).

In_ a related study, Gopalan and Young (1975) examined "shell
disease" in the caridean shrimp, Crangon septemspinosa, an
estuarine and coastal food chain organism common on the east
coast of North America and important in the diets of bluefish,
weakfish, flounders, sea bass, and other economic species.

Sgstrella, B. T. (pers. commun., October 1988) has provided some
interesting new observations about sheil disease in rock crabs
(Cancer irroratus) from polluted ‘sites. He pointed out that
extensive erosion of the carapace often occurs over the gills,
possibly because the relatively inefficient gill bailer system of
the crabs allows accumulation of contaminated sediments and
associated microorganisms in the gills, with the possibility of
chitin destruction proceeding from the gill chamber upward.
According tc this hypothesis, lobsters, with a more efficient
mechanism for water movement over the gills, would have fewer of
these extensive carapace lesions over the gills (and this seemed
to be the case in Estrella's extensive sampling in Massachusetts
waters). Estrella also suggested other possible reasons for high
prevalences and severity of shell disease in rock crabs——
including behavioral effects related to burrowing in contaminated
sediments, and effects of possible species differences in shell
pore structure.

-22-



ABSTRACT

The shell disease Syndrome has been reported from Many
freshwater and marine crustaceans of economic importance. Signs
of the disease syndrome include erosion and pitting of the
exoskeleton, resulting from activities of chitin-destroying
microorganisms--bacteria and fungi of several genera. Infection
is usually limited to the exoskeleton, although underlying living
tissues may be invaded by other opportunistic microbial
pathogens.

Shell disease is usually relatively rare in natural
populations, although a few epizootics have been reported. High
prevalences occur in captive populations, especially in
overcrowded holding facilities, probably because of greater
likelihood of damage to the cuticle and the presence of other
abnormal environmental conditions, including organic loading with
consequent high bacterial populations.

Mortalities from shell disease have been observed,
occasionally at high levels, in impounded populations.
Destruction of gills and adhesions of the exoskeleton which

Prevent ecdysis have been considered to be responsible factors, .

as have secondary systemic infections which develop after
perforation of the- chitinous integument.

“Shell disease has been observed in crustaceans from badly
degraded coastal/estuarine waters, often associated with so-
called "black gill" syndrome. Exoskeletal erosions are common in
lobsters, crabs, and smaller erustaceans from areas where
contaminated sediments occury and the shell disease Syndrome has
been produced experimentally by exposure of normal animals to
sediments from sewage sludge and dredge spoil disposal sites.
Organic loading in degraded waters, with consequent increases in
populations of heterotrophic bacteria--some of which may be
facultatively Pathogenic--may be a significant factor.

—Shell erosion in Crustacea is, -therefore, a particular
Problem in impoundments,. in aquaculture facilities, and in
degraded habitats. It is contagious, but its etiology is
complex, involving chitinoclastic and other microorganisms and
environmental stressors.~ It may contribute to mortality,
principally by providing a‘route of entry for other facultative
Pathogens, but also by destroying the gills of erustacean hosts
and by interfering with molting.



ROBINSON, R. K. & D. E. DIMITRIOU. 1963. The status of the
Florida spiny lobster fishery, 4962-63. Fla. Board
Conserv., Tallahassee, Tech. Ser. No. 42, 30 pp.

ROSEN, B. 1967. Shell disease of the blue crab, Callinectes
Sapidus. J. Invertebr. Pathol. 9: 348-353.

ROSEN, B. 1970. Shell disease of aquatic crustaceans, pp. 409-
415. In Snieszko, S. F. (Ed.), A Symposium on Diseases of
Fishes and Shellfishes. Am. Fish. Soc. Spec. Publ. 5,
Washington, D.C.

ROSENFIELD, A. 1976. Infectious diseases in commercial
shellfish on the middle Atlantic coast, pp. 414-423. In
Gross, M. G. (Ed.), Proceedings of the Symposium on the
Middle Atlantic Continental Shelf and the New York Bight.
Am. Soc. Limnol. Oceanogr. Spec. Symp. 2.

SANDIFER, P. A. & P. J. ELDRIDGE. 1974, Observations on the
incidence of shell disease in South Carolina blue crabs,
Callinectes sapidus, pp. 161-184. In Amborski, R. L., M. A.
Hood & R. R. Miller (Eds.), Proceedings of Gulf Coast
Regional Symposium on Diseases of Aquatic Animals.
Louisiana State Univ. Publ. No. LSU-SG-74-05, Baton Rouge.

SAWYER, T. K. 1982. Distribution and seasonal incidence of
"black gill" in the rock crab, Cancer irroratus, pp. 199-
211. In Mayer, G. F. (Ed.), Ecological Stress and the New
York Bight: Science and Management. Estuar. Res. Fed.,
Columbia, South Carolina.

SAWYER, T. K., S. A. MACLEAN, J. &. BODAMMER, & B. A. HARKE.
1979. Gross microscopical observations on gills of rock
crabs (Cancer irroratus) and lobsters (Homarus amezicanus)
from nearshore waters of the eastern United States, Pp. 68-
91. in Lewis, D. H. & J. K. Leong (Eds.), Proceedings of
the Second Biennial Crustacean Health Workshop. Texas A&M
Univ. Sea Grant Publ. No. 79-114.

SAWYER, T. K., E. J. LEWIS, M. GALASSO, S. BODAMMER, J.
ZISRKOWSKI, D. LEAR, M. O'MALLEY & S. SMITH. 1983. Black
gill conditions in the rock crab Cancer irroratus, as
indicators of ocean dumping in Atlantic coastal waters of
the United States. Rapp. P.-V. Reun. Cons. Int. Explor. Mer
182: 91-95.

SAWYER, T. K., E. J. LEWIS, M. E. GALASSO & J. J. ZISKOWSKI.
1984. Gill fouling and parasitism in the rock crab, Cancer
irroratus Say. Mar. Environ. Res. 14: 355-369.



LIGHTNER, D. V., C. T. FONTAINE & K. HANKS. 1975. Some forms of
gill disease in penaeid shrimp. Proc. World Maricult. Soc.
6: 347-365.

LIGHTNER, D. V., L. B. COLVIN, C. BRAND & D. A. RANALD. 1977.
Black death, a disease syndrome of penaeid shrimp related to
a dietary deficiency of ascorbic acid. Proc. World
Maricult. Soc. 8: 611-623.

LIGHTNER, D. V., B. HUNTER, P. C. MARGARELLI, JR. & L. B.
COLVIN. 1979a. Ascorbic acid: nutritional requirement and
role in wound repair in penaeid shrimp. Proc. World
Maricult. Soc. 10: 513-528.

LIGHTNER, D. V., D. MOORE & D. A. DANALD. 1979b. A mycotic
disease of cultured penaeid shrimp caused by the fungus
Fusarium solani, pp- 135-158. In Lewis, D. BH. & J. K. Leong
(Eds.), Proceedings of the Second Biennial Crustacean Health
Workshop. Texas A&M Univ. Publ. No. TAMU-SG-79-114.

MALLOY, S. C. 1978. Bacteria induced shell disease of lobsters
(Homarus americanus). J. Wildl. Dis. 14: 2-10.

MANN, 4H. 1940. Die Brandfleckenkrankheit beim Sumpfkrebs
(Potamobius leptodactylus Eschh.). 2. Parasitenkd. ll: 430-
432.

MANN, 3. & OU. PIEPLOW. 1938. Die Brandfleckenkrankheit bei
Krebsen und ihre Erreger. 2Z. Fisch. 36: 225-240.

MARTINEZ, L. E., A. M. MOLINARES, J. VILLANUEVA & D. A. CONROY.
1982. Preliminary observations on the application of
nifurpirinol for the control of potential disease problems
in Macrobrachium acanthurus, pp. 285-289. In New, M. B.
(Ed.), Giant Prawn Farming. Elsevier Sci. Publ., Amsterdam,

MCLEESE, D. W. 1965. Lesions on the abdominal membrane of
lobsters. J. Fish. Res. Board Can. 22: 639-640.

MCLEESE, D. W. & D. G. WILDER. 1964, Lobster storage and
shipment. Fish. Res. Board Can. Bull. 147, 40 pp.

MEARNS, A. 1973. Exoskeletal lesions in crabs, pp. 303-304. in
The Ecology of the Southern California Bight: Implications
for Water Quality Management. South. Calif. Coastal Water
Res. Proj., Rep. No. TR104, El Segundo, California.

MEIXNER, R. 1969a. Wachstum, H&utung, und Fortpflanzung von

Crangon crangon (L.) bei Einzelaufzucht. Ber. Dtsch. Wiss.
Komm. Meeresforsch. 20: 93-111.

-39-



Table 2 (continued).

Geographic Common name Pathogens
Host location of disease isolated References
Shrimp Northeastern Shell disease Not - Gopalan &
(Crangon U.S. coast reported Young, 1975
septemspinosa)
Pacific white Florida . Not Cook &
shrimp (Penaeus (in culture reported Lofton,
occidentalis); ponds) . 1973;
white shrimp Iversen &
(Penaeus Beardsley,
setiferus) 1976
Penaeus spp. Ubiquitous Bacterial Vibrio, Cook &
shell disease Aeromonas, Lofton,
(brown spot) Spirillun, 1973;
Pseudomonas, Couch, 1978;
Flavo- Cipriani et
- bacterium al., 1980;
Lightner,
1988a
Penaeus spp. Ubiquitous Fungal shell Fusarium Lightner,
in culture disease Spp., 1975, 1988a;
environments (associated especially Lightner et
with a F. solani al., 1979b;
disease (other fungi Solangi &
condition such as Lightner,
known as Haliphthoros 1976
“black gill" sp. and
in Penaeus Atkinsiella
japonicus) dubia may be
(Kuruma isolated—but
prawn) rarely) -
English prawn U.K., Brown spot Chitino- Anderson &
(Palaemon France disease clastic Conroy,
serratus) bacteria 1968;
Campillo,
-1976
-9-

aed er



coastal/estuarine waters and damage to non-target crustaceans by
interference with chitin synthesis. Evidence for this
possibility has been provided by recent experimental studies.
One of the reported effects of exposure of fiddler crabs, Uca
pugilator, to diflubenzuron was blackened lesions on regenerating

appendages--areas that were "soft to the touch" (Weis et al.,
1987). The authors suggested that the lesions May reflect
deficiency in chitin formation, but they did note a resemblance
to “shell disease" as described from crabs and lobsters in the
New York Bight by Young and Pearce (1975). Another experimentai
study, in which barnacles, Balanus eburneus, were exposed to
diflubenzuron disclosed lesions in the form of “cuticular
disruptions" in cast exoskeletons (Gulka et al., 1982). In some
specimens both the exocuticle and the endocuticle were disrupted;
cast exuvia of diflubenzuron-treated animals were consistently
more fragile; and molting was frequently inhibited. Since in
both these studies the lesions appeared very soon after molting,
mechanisms other than chitin destruction by microorganisms were
probably operative--mechanisms which might include interference
by pollutants in the biochemistry of cuticle formation, or in
energy transfers within the organism. It seems possible that
other less specific pollutants could act in similar ways.

A final cautionary note seems pertinent to this discussion
of the etiology of shell disease. Crustaceans, particularly
those that have just molted, are vulnerable to injuries from
contacts with predators or other members of the species--injuries
which may take the form of losses of spines or damage to larger
portions of the carapace. Such mechanical losses may sometimes
mimic the effects of shell disease (and may, of course, act as
portals of entry for pathogens).

To summarize information about etiology, the shell disease
syndrome may be the result of:

° Chitinolytic, lipolytic, and proteolytic activity of
microorganisms--principally bacteria and fungi--acting
alone or in combination on injured or intact cuticle;

° Interference with chitin synthesis, by inadequate
nutrition or by biochemical effects of pollutants such
as certain pesticides with specific activities; and

° Activity of stressors in the environment~-especially
high population densities, abnormal temperatures and
Salinities, presence of toxic chemicals, and hypoxia--
acting to disturb metabolic processes and internal
defense mechanisms of the host.

Prom the foregoing, it appears that damage to the
epicuticle, or suppression of cuticular repair because of
inadequate diet or other stressors, can, in the presence of high
densities of chitinolytic microorganisms, enhance the development

moet TS ae



NOAA Technical Memorandum NMFS-F/NEC-64

This TM series is used for documentation and timely communication of preliminary results,
interim reports. or special purpose information. and has not received complete formal
review. editorial control, or detailed editing.

The Shell Disease Syndrome
in. Marine Crustaceans

Carl J. Sindermann
Oxford Lab., National Marine Fisheries Serv., Oxtord, MD 21654

U. S. DEPARTMENT OF COMMERCE
Robert A. Mosbacher, Secretary

National Oceanic and Atmospheric Administration
William E. Evans, Administrator
National Marine Fisheries Service
James W. Brennan, Assistant Administrator for Fisheries
Northeast Fisheries Center
Woods Hole, Massachusetts

February 1989



Some evidence exists for an association of the shell disease
syndrome and habitat degradation. Prevalences have been found to
be high in samples from polluted sites; prevalences show trends
similar to those of the black gill syndrome, which has a
statistical association with extent of pollution; and
experimental exposures of crustaceans to contaminated sediments,
heavy metals, biocides, petroleum, and petroleum derivatives can
result in the appearance of the black gill syndrome, often
accompanied by shell disease. It is important to note, however,
the cautionary words of Ayres and Edwards (1982), pointing out
that dumpsites are rarely fished intensively, and hence would
have more larger and older animals which molt less frequently,
and hence, could have higher prevalences of shell disease. (This
avoidance phenomenon exhibited by European crab fishermen, as
described by Ayres and Edwards, May not, however, apply to the
lobster fishery on the northeast coast of United States, where
the vicinities of domestic sewage outfalls or sewage sludge
dumpsites can be favored locations for traps.) It is also
important to keep in mind the observation of Sawyer (1982) and
Sawyer et al. (1985) that season, stage of the molt cycle, and
differential migrations may have profound effects on prevalences
of the black gill condition (and, by analogy, on prevalences of
shell disease). - -

The shell disease syndrome exemplifies a condition at the
boundary between infectious and noninfectious disease
processes. This is the area where environmental stressors and
facultative microorganisms exert their impacts; where high
bacterial populations in eutrophic waters interact with exposed,
or injured, or chemically modified surface layers; where normally
harmless epibiotic fouling organisms can assume pathogenic roles;
and where nonspecific lesions such. as exoskeletal erosions can
occur in epizootic proportions. Prevalence of the shell disease
syndrome in Crustacea may well prove to be an excellent indicator
of abnormal environmental conditions, and a measure of stress on
individuals. Ingredients to be considered are presence of toxic
chemicals, large populations of facultatively pathogenic
microorganisms, inadequate nutrition, extremes of Salinity and
temperature, and existence of anoxic or hypoxic conditions.

The appearance of shell erosion may therefore be the

consequence of a disturbed balance between processes of chitin
maintenance and repair and the activities of chitinoclastic
microorganisms--this disturbance created by either natural or
man-made environmental changes. Critical to an understanding of
the relationship are environmental, genetic, and immunological
factors which may either promote repair or, conversely, .enhance
exoskeletal degradation. Also essential to full understanding of
the shell disease syndrome are further experimental studies,
Particularly those concerned with identification of specific
microorganisms capable of pathogenesis, experimental. manipulation

of predisposing environmental variables, and the. immunologic
responses of hosts to cuticular disruption.

~32-



V. THE SHELL DISEASE SYNDROME IN
CRUSTACEAN AQUACULTURE

Among aquaculture populations, the shell disease syndrome
has been observed and reported principally in penaeid and other
shrimp, probably because they are the major farmed marine
erustacean species on a worldwide basis--although experimental
and pilot-scale culture of lobsters and crabs has also
encountered problems with the Gisease syndrome.

Shell disease of possible bacterial etiology in English
prawns, Palaemon serratus, was described briefly by Anderson and
Conroy (1968). Labeled “brown spot disease" and characterized by
erosion and destruction of the exoskeleton, the disease was
Particularly evident in crowded culture tanks. Although the
etiology was undetermined, the authers observed an association
between the occurrence of spots and the presence of
myxebacteria. In a later study (Campillo, 1976), chitinoclastic
bacteria were identified as the cause of "brown spot" of
prawns. The disease condition was rare in wild-caught samples,
but developed rapidly in captive populations. Mortalities were
observed, and were attributed to combined effects of the bacteria
and a ciliate, Ascophrys rodor, which also perforated the cuticle
of the prawn (Campillo and Deroux, 1974).

Prevalences of brown spot disease in Gulf of Mexico shrimp
(Penaeus aztecus and P. setiferus) were reported to be 2.5% in
matural ‘populations “and 10.5% in an aquaculture facility
(Cipriani et al., 1980). Even higher prevalences--up to 60%--
were seen in temporary holding tanks, and some mortalities (2.8%)
were attributed to the disease. The authors suggested, however,
that reported high mortalities due to shell disease in
aquaculture systems may actually be due to other factors, such as
the presence of unrelated systemic microbial infections. Brown
spot disease of penaeid shrimp is usually considered to be of
bacterial etiology. However, invasion of the exoskeletcn by the
fungus Fusarium has been described in cultured shrimp (Lightner
1981). Presence of the fungus invokes a strong host response-
inflammation and melanization--which may circumscribe the
infection but which leads to formation of adhesions that prevent
molting and thus cause death (Solangi and Lightner, 1976).

The shell disease syndrome is also common in cultured
freshwater prawns, Macrobrachium rosenbergii, and has been
implicated in hatchery mortalities (Aquacop, 1977; Martinez et
al., 1982; El-Gamal et al., 1986). In the work of El-Gamal et
al., the bacterium Aeromonas hydrophila was the most consistent
isolate from areas of exoskeletal erosion in adults. Prominent
burn spot lesions were reported to reduce the value of prawns
Marketed in Southeast Asia by 75%,



Recent issues in this series

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3 tables, 4 app. NTIS Access. No. PB89-100903/AS.

. 56. Characterization’ of the Middle Atlantic Water Management Unit of the Northeast Regional Action Plan. By
Anthony L. Pacheco, ed. July 1988. v + 322 p., 136-figs., 21 tables.

57. AnAnalysisand Evaluation of Ichthyoplankton Survey Data fromthe Northeast Continental Shelf Ecosystem.
By7vallace.G. Smith, edt August 1988_xit, + 2p, 53 figs., 12 tables, 1 app. NTIS Access. 'No. PB89-12250V/AS.

Indexed Bibticgeaphy of Northeast Fisheries Center Publications: aud Reports for 1987. By Jon A. Gibson.
‘Access. No. PB89-LI30LV/AS.-

Breeding | ‘Penguins.and ‘Other Seabirds i in the South Shetland Islands, Antarctica, January-
|Shuford and Larry B. Spear. September 1988. vii + 27p_ 14figs. | table. NTIS Access

‘Shetland’ Islands, Antarctica. doring the1386-1987 ‘amstral: Summer.

ss No: BBS9-141303/AS. Ba a

siihtes


(5) Darkening of hemolymph in gill lamellae and in areas
where degenerative changes were occurring; and

(6) Attainment and maintenance of "“heterostasis"--an
abnormal level of equilibrium in the continued
presence of a toxic stressor--promoted by enhanced
detoxifying activity of the hepatopancreas and
excretory activity of the antennal gland.

These responses may be important to survival of crustaceans
in degraded habitats, and are often associated with cuticular
erosions, especially of the gills.

VII. DISCUSSION AND CONCLUSIONS

The shell disease syndrome has been reported from many
crustaceans, including a number of the larger economically
important species of crabs, shrimp, and lobsters. The disease
condition appears to be a stress and injury-related phenomenon,
characterized by degradation of the chitinous exoskeleton by
lipolytic, chitinolytic, and proteolytic exoenzymes of
microorganisms acting independently or in concert. Bacteria are
most frequently described as principal pathogens, but fungi have
been implicated as well. Bacterial infections seem to
predominate in marine crustaceans, whereas fungal infections are
often reported in freshwater forms.

The shell disease syndrome occurs, usually at low levels, in
natural populations, but its effects may be enhanced and
prevalences increased in crustacean populations under stress from
environmental degradation, or in populations in which individuals
are crowded abnormally—in impoundment facilities or in
aquaculture grow-out tanks.

Effects of the disease may be enhanced by (1) overcrowding
er handling, which increases the likelihood of cuticular
abrasions, (2) stresses from abnormal environments, and (3) high
erganic loading of containment waters, which contributes to
multiplication of heterotrophic microbial populations--some of
which may be facultatively pathogenic to crustacean hosts.

The disease is contagious and progressive, but effects are
usually confined to erosion of the exoskeleton, except when
underlying living tissues are exposed and invaded by other
opportunistic microorganisms. In some species, ecdysis can
terminate infections (although reinfections may occur). The rate
of exoskeletal destruction is probably variable with species or
strains of pathogens, nutritional state of the host, density of
pathogen populations, and other environmental factors, such as
temperature.

crema se oe earthen Pte ge


FISHER, W. S., EB. 8. NILSON, J. F. STEENBERGEN & D. V.
LIGHTNER. 1978. Microbial diseases of cultured lobsters:
a review. Aquaculture 14: 115-140.

FONTAINE, C. T., R. G. BRUSS, I. A. SANDERSON & D. V. LIGHTNER.
1975. Histopathological response to turpentine in the white
shrimp, Penaeus setiferus. J. Invertebr. Pathol. 25: 321-
330.

FORSTER, J. R. M. & J. F. WICKINS. 1972. Prawn culture in the
United Kingdom. Minist. Agric. Fish., Food Lab Leafl.
(N.S.) No. 27, 31 pp.

GOPALAN, U. K. & J. S. YOUNG. 1975. Incidence of shell disease
in shrimps in the New York Bight. Mar. Pollut. Bull. 6:
149-153.

GORDON, I. 1966. Parasites and diseases of Crustacea. Men.
Inst. Fondam, Afr. Noire No. 77: 27-86.

GULKA, G., C. M. GULKA & N. WATABE. 1982. Histopathological
effects of diflubenzuron on the cirripede crustacean,
Balanus eburneus. Arch. Environ. Contam. Toxicol. 11: 11-

26.
HAPPICH, A. 1900, Vorlaufige Mitteilung Ober eine neue
Krankheit der Krebse. Baltische Wochenschrift £.

Landwirtschaft, Gewerbefleiss und Handel Nr. 47. Dorpat.

HESS, E. 1937. A shell disease in lobsters (Homarus americanus)
caused by chitinovorous bacteria. J. Biol. Board Can. 3:
358-362.

HIBBITS, J., G. C. HUGHES & A. K. SPARKS. 1981. Trichomaris

invadens gen. et sp. nov., an ascomycete parasite of the
tanner crab (Chionoecetes bairdi Rathbun Crustacea;
Brachyura). Can. J. Bot. 59: 2121-2128. “

HOCK, C. W. 1940. Decomposition of chitin by marine bacteria.
Biol. Bull. 79: 199-206.

HOCK, C. W. 1941. Marine chitin-decomposing bacteria. J. Mar.
Res. 4: 99-106.

HOOD, M. A. & S. P. MEYERS. 1974. Distribution of
chitinoclastic bacteria in natural estuarine waters and
aquarial systems, pp. 115-121. In Amborski, R. S., M. A.
Hood & R. R.~ Miller (Eds.), Proceedings of Gulf Coast
Regional Symposium on Diseases of Aquatic Animals.
Louisiana State Univ. Publ. No. LSU-SG-74-05, Baton Rouge.

-37-



wert

Examinations of samples of Crangon from the New York Bight apex
disclosed high prevalences (up to 15%) of eroded appendages and
blackened erosions of the exoskeleton. The disease condition was
only rarely observed at other collecting sites (Beaufort, North
Carolina and Woods Bole, Massachusetts). Histological
examination of diseased specimens produced findings similar to
those of Young and Pearce (1975) with crabs and lobsters. All
layers of the exoskeleton were eroded; affected portions were
brittle and easily fragmented; cracking and pitting of calcified
layers occurred; and underlying tissues were often necrotic.
Laboratory experiments using seawater from the highly polluted
inner New York Bight resulted in appearance of the disease in 50%
of individuals. Erosion was progressive, crippled individuals
were cannibalized, and eroded segments of appendages did not
regenerate after ecdysis. No disease signs developed in control
animals held in artificial seawater.

A counterpart German study of the effects of industrial
wastes on the brown shrimp, Crangon crangon (Schlotfeldt, 1972),
disclosed high prevalences of so-called “black spot disease,"
with signs very similar to those seen in C. septemspinosa from
the New York Bight. Juvenile and adult shrimps from the polluted
FOBhr Estuary had black areas of erosion on the carapace and
appendages, with necrosis of underlying tissues, and, frequently,
missing terminal segments of appendages. The disease condition
varied in prevalence seasonally, with a peak of 8.9% in summer.
Lesions persisted and worsened after ecdysis, and experimental
exposure to detergent accelerated the course of.,the disease.
Another study of Crangon crangon in the Burry Inlet, Wales (U.K.)
disclosed a disease condition known as “black necrosis," with
higher prevalences in larger shrimp (Abbott, 1977). Earlier,
Meixner (1969a, b) had observed localized blackened areas, and
injured appendages in Crangon taken in the German shrimp fishery,
and higher mortality of affected individuals held in laboratory
tanks.

A long-term study of the effects of waste discharges along
the southern California coast (Southern California Coastal Water
Research Project) has included examination of shell disease in
crustaceans. In the early years of the project (1971 and 1972),
an exoskeletal disease resembling "burn spot disease" was
reported in the crabs Mursia gaudichaudii and Cancer sp. (Mearns,
1973). Samples of M. gaudichaudii collected in 1972 along the
150-m contour on the Palos Verdes shelf had. 8% blackened
exoskeletal lesions, while in similar depths in Santa Monica Bay
the prevalence was 44%. According to Mearns, the disease seemed
to be localized in populations of small crabs near the heads of
submarine canyons, although small samples of larger crabs from
inshore stations disclosed prevalences of up to 70%.



Table 2 (continued).

Geographic Common name Pathogens
Host location of disease isolated References
CRABS
Blue crab Louisiana, Shell disease Vibrio, Overstreet
Callinectes Mississippi Pseudomonas & Cook,
Sapidus) 1972;
Cook &
Lofton,
1973;
Overstreet,
1978
. Florida . Not Iversen &
reported Beardsley,
1976
. South " Not Sandifer &
Carolina reported Eldridge,
1974
. Chesapeake TM Chitino— Rosen, 1967,
Bay clastic 1970
bacteria
Shore crab Southwest Black spot Not Schaperclaus,
(Cancer coast of shell disease; reported 1935;
pagurus) Ireland; shell necrosis; Gordon,
England black necrosis; 1966;
burn spot Bakke, 1973;
disease Ayres &
Edwards,
1982
. Norway Shell disease Not Bakke, 1973
reported
Rock crab Northeast Shell Not Sawyer,
(Cancer coast of blackening, reported 1982
irroratus) U.s. carapace
erosion
Stone crab Florida Shell disease Not Iversen &
(Menippe reported Beardsley,
mercenaria) 1976

-7-



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‘ .. programs of. basic and applied research to: (1) better understand the living marine resources (including marine
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are a normal part of the aquatic environment, and they can be
found on the body surfaces and in the shell pores cf
crustaceans. Some, such as Vibrio parahaemolyticus adsorb
readily to chitin, where they may form microcolonies which
degrade and utilize the substrate (Kaneko and Colwell, 1973,
1975). Chitinoclastic microorganisms may become opportunistic
pathogens of stressed or damaged individuals, and may increase in
numbers dramatically in aquaculture facilities or in polluted
waters. Participating microorganisms have been shown to produce
extracellular lipases, chitinases, and proteases (Lightner,
1988a).

In earlier studies with European freshwater crustaceans,
several fungi (including Ramularia astaci, Septocylindrium
eriocheir, and Didymaria cambari) were isolated from shell

lesions, and were thought to be the primary etiological agents of
shell disease--called "Brandfleckenkrankheit" (Mann and Pieplow,
1938; Unestam, 1973), whereas in North America, beginning with
the studies of Hess (1937) on shell disease in lobsters, bacteria
have been reported as the usual causes of the syndrome (Rosen,
1970; Amborski et al., 1975; Baross et al., 1978; Malloy,
1978). Fungi are not uncommon, however, in exoskeletal lesions
of marine or freshwater crustaceans; they may be primary or
secondary invaders (Alderman, 1973; Burns et al., 1979; Johnson,
1983; Alderman, 1987). Some recent publications on shell disease
in Crustacea have discussed available information on the basis of
two major subcategories: "fungal shell disease“ and “bacterial
shell disease" (Johnson, 1983; Alderman, 1987; Austin and
Alderman, 1987). This may be a useful descriptive device, but
the precise etiology of shell disease is in too many cases
uncertain enough to discourage such an exclusive categorization
(at least in this document). A succinct description of the
participants in the shell Gisease syndrome was given by Cipriani
et al. (1980). "The lesion [exoskeletal erosion] appears to be a
microenvironment in which several microbial taxa, producing a
variety of degradative exoenzymes, interact to create the disease
signs."

One possible key to outbreaks of shell disease syndrome was
pointed out by Fisher et al. (1976), Fisher et al. (1978), and
Malloy (1978)--that maintenance and repair of the epicuticle was
critical in reducing the occurrence of exoskeletal erosions, and

that stressors such as inadequate nutrition, temperature
extremes, or onset of ecdysis resulted in higher levels of the
disease condition.

Another insight of possible importance is that some
conditions referred to as “shell disease" might have a more
direct relationship to environmental pollutants, and might not be
related at all to effects of chitinoclastic microorganisms. AS

an example, recent use of insect growth regulators, a class of
less persistent pesticides which includes diflubenzuron
(commercial name, Dimlin), could result in contamination of