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Ashland NFWCO
 Midwest Region
 Dedicated To The Tribal Aquaculture ProgramImage of fish jumping.
    December
        2002-Volume 42
**Administrative
        Coordinator:
        Frank G. Stone 
        (715-682-6185) Ext.
        202
        U.S. Fish and
        Wildlife Service
        Email: 
        [email protected]**
      **Edited
        By:
        Elizabeth W. Greiff 
        (715-349-2195) Ext. 141
        St. Croix Tribal Nat. Res. Depart.
        Email:**
      **[email protected]** Topics
Of Interest: Fish Health Management for Intensive Fish Farming Gill Diseases of Fish Expandable Fiberglass Rearing Tanks Fish
Disease Treatments  Fish Health Management for Intensive Fish Farming (Abstract)
By:  George W. Klontz, D.V.M. The two articles that follow were
obtained from the Nelson's Silver Cup Fish Feed
web page as part of their free download informational series. Extrinsic Factors Affecting Fish Health
The extrinsic or environmental factors which are known to compromise the
health status of fish individually or collectively can be grouped into the
following categories according to their location within the system: (1)
water-associated; (2) pond-associated; (3) nutrition-associated; (4)
management-associated. To some, this classification scheme may seem somewhat
simplistic and/or conceptual. Nonetheless, the process of investigating the
nature of a disease episode has been enhanced by identifying and quantifying the
associated factors. The quantitative evaluation of the prime factors has
permitted the raising of fish with a minimum of problems.
(1) Water-associated factors: Among water-related factors identified as
affecting the productivity of aquaculture systems, water temperature and
dissolved oxygen content have the most significant insidious effects on fish
health. They are inherent in all water supplies and are subject to fluctuations
to which the fish in the system must adapt. The physiological effects of the
fluctuations are very broad, ranging from a change in metabolic rate to altering
the susceptibility to pathogens. In this regard, the documentation of
environmental changes and the occurrences of infectious and noninfectious
disease processes could be an invaluable aid in predicting the likelihood of a
subsequent disease episode. Examples of this are legion but not sufficient to be
a widespread practice.
(2) Pond-associated factors: The primary effect here is requiring a
particular fish to live in a pond configuration which does not meet its
behavioral requirements.
(3) Nutrition-associated factors: One would think that in this day and age of
high quality commercial diets, nutritional problems would not occur, but they
do, all too frequently.  Our studies over the past 4-5 years on production
forecasting have shown the health of fish can be compromised when the fish are
fed at a rate permitting less than 80% of the Allowable Growth Rate. We have
found growth rate to be a very reliable indicator of the health of the
population. Deviations of as little as 1% from the expected growth rate can be
measured quite accurately and evaluated with a high degree of statistical
validity.
Overfeeding a population is another health-compromising situation. In this
case there are frequently abnormal amounts of abdominal fat and hepatic glycogen
deposits. The effects are not often seen immediately, but can be implicated in
the milieu of casual factors of an unhealthy state.
(4) Management-associated factors: The primary health-threatening factors in
this category emanate from exceeding one or more of the pond carrying
capacities, from inadequate housekeeping practices, from inadequate
record-keeping practices, and from undue physical stressors.
Intrinsic Factors Affecting Fish Health
The intrinsic or somatic factors originate within the fish itself. They are
largely governed by the genetic make-up which by and large dictates the
physiological and psychological responses of the fish to the extrinsic
factors.
Perhaps the major intrinsic factor which fish health managers have some
control over is the generation of endogenous ammonia (NH ). We all know that
free ammonia (NH ) is deleterious to the health of fish when specified limits are exceeded. The
main impact, as we now understand it, is on the gill lamellae in the form of
epithelial hypertrophy and hyperplasia which reduce the oxygen uptake by the
fish, thus impacting the physiological well-being of the fish. The control of
this process is to reduce the dietary protein, or to decrease the retention time
of ammonia in the pond by increasing the water flow, or to reduce the population
of fish in the pond, or to reduce the water temperature, or to decrease the pH
of the system. Any one of the foregoing will serve to preserve the health of
fish, within limits. A second intrinsic factor over which we can exercise some
control is the healthy or chronic asymptomatic carrier of infectious agents. It
is apparent from our studies with Renibacterium salmoninarum and Aeromonas
salmonicida carriers that the presence of these bacteria within the fish
negatively impact their growth potential and represent a measurable threat to
the uninfected portion of the population.
Summary and Conclusions
Up to this point, this presentation has been rather gloomy, in my opinion.
But, we must face reality - we could do better with preserving the health of our
fish if we only would. To that end, I would offer the following as food for
thought, and, hopefully, subsequent action by both the fish farming community
and the fish health management profession, collectively.
1. Practice preventive medicine through detection and elimination of the
carrier states of bacterial and viral pathogens, through mass immunization of
fish against pathogens, through implementation and maintenance of
health-preserving management practices, and through implementation and
enforcement of live fish transportation regulations.
2. Apply the principles of epidemiology to investigations of disease
occurrences.
3. Maintain open lines of communication among all facets of the aquaculture
community.

 
Gill Diseases of Fish
By:  George W. Klontz, D.V.M.
Introduction
The gill diseases of fish under confined farm ponds or raceways, and
free-living conditions are very complex and, in many cases, not well understood
from epidemiological and etiological standpoints. This group of diseases, in the
opinion of many, is one of the major production-limiting factors in farmed
fishes. Subclinical episodes are often quite difficult to detect due to their
insidious onset. Clinical episodes are frequently dramatic in terms of the
mortality involved, which has a rapid onset and often an exponential daily
increase.
One of the major cost-incurring factors in this group of diseases is the
chemotherapeutic regimens, which could best be described as
"categorical." That is, fish with the clinical signs of rapid, shallow
respiratory movements, grossly enlarged gill tissues, and incomplete opercular
closure are "treated" with one of the many chemicals added to the pond
water. The results have ranged from "rewarding" to "well, we
guessed wrong." the latter cases could have been prevented, perhaps, by
elucidating the nature of the problem prior to treatment.
Nature of Gill Diseases of Fish
The known causal factors in gill diseases of confined and free-living fishes
are myriad. These factors can be grouped into those which are (1) infectious or
are (2) noninfectious, with each group being further subdivided into those
factors which are primary and those which are secondary.
The primary causal factors are those which have a direct effect on the
respiratory tissues and/or processes. Included in this group are the nonsystemic
myxobacteria, eubacteria and fungi, the external protozoans and monogenetic
trematodes, the water-borne chemical and physical agents, and the genetic and
nutritional factors.
The secondary causal factors are those which affect the respiratory tissues
and processes indirectly. Included in this group are the systemic bacterial and
viral pathogens, the systemic protozoans and digenetic trematodes, the
environmental chemical and physical stressors and certain metastatic neoplastic
processes. These factors, in most cases, exert their pathogenic capabilities
throughout the body with the gill involvement being just a part of the somatic
process.
The major factors predisposing fish to subclinical or clinical episodes of
gill diseases are (1) the stress response; (2) age; (3) environmental conditions
favoring the proliferation of infectious agents; i.e., myxobacteria, eubacteria,
protozoa and fungi. The three factors are virtually always involved in clinical
episodes.
The stress response, particularly to chronic stressors such as high
population densities, has been shown to create pathological changes in the gill
tissues which are conducive to the involvement of secondary infectious and/or
noninfectious factors.
The susceptibility to noninfectious and infectious respiratory
disease-inducing factors decreases with age. The highest incidence of
respiratory diseases occurs in the sac fry stage during which the most common
malady is sestonosis with subsequent myxobacterial and protozoal involvements.
This condition is typified by the accumulation of particulate materials and
fungal elements on the buccal aspect of the gill rakers. Death is usually by
suffocation. Because of its nature, sestonosis is virtually untreatable.
Strict cleanliness is the only sure method of prophylaxis. The bacterial gill
diseases are quite common in populations of fishes from the fingerling stage
through the mid-juvenile stage. This group of maladies is most frequently a
sequel to a noninfectious process, environmental gill disease (EGD). The EGD
syndrome is considered to be, first, stress-mediated and, second,
environmentally-mediated. By itself; i.e., uncomplicated by pathogens or
noninfectious factors, it is more a debilitating process than it is lethal. This
aspect is, perhaps, what makes it such an economically significant disease
process. There is no specific recommended treatment regimen largely because the
causal factors are often quite obscure, if evident at all.
Pathological Changes in Respiratory Diseases of Fish
A. Noninfectious causal factors: The gross and microscopic pathological
changes in gill tissues, especially the lamellae, are dose response dependent.
The inflammatory process ensuring from the initial exposure begins with lamellar
epithelial hypertrophy in which there is focal-to- generalized involvement of
the squamous epithelial cells. If the irritant exposure is short-lived, the
hypertrophic condition subsides within a few days, usually without notice.
B. Infectious causal factors: The pathological changes associated with direct
and indirect infectious causal factors are often quite confusing for the
diagnostician. In the directly associated causal factors the pathogen usually
occupied an opportunistic role. That is, it "sets up housekeeping" on
gill tissues already affected by some moderately long-standing noninfectious
process.
Prevention and Control of Respiratory Diseases of Fish
There are several approaches to preventing and controlling respiratory
disease episodes in confined fish populations. The first is avoidance of the
conditions which are conducive to the occurrence of subclinical and clinical
episodes. This is best accomplished by (1) maintaining the fish within the
environmental "no-effect" limits with respect to settleable and
suspended solids, ammonia-nitrogen, dissolved oxygen and population density and
by (2) routine examination of gill wet mounts, production data and feed
conversion ratios.
The "no-effect" limits of environmental factors have been
established for some species of salmonids under certain, albeit limited,
conditions. The best suggestion is for the individual aquaculturist to establish
the unique limits for his/her facility. To accomplish this one must establish a
protocol for measuring the environmental parameters and their effects on fish
growth and gill tissues. This process should begin with sac fry and continue
throughout the production cycle. One caveat is that the process is
time-consuming and often frustrating, but always rewarding in the long term.
During the process of establishing the specific "no-effect" limits
of environmental parameters, wet mounts of gill tissues must be examined on a
regular basis. Fish should be taken from the "healthy" and the
"unhealthy" or "sickly" portions of the populations. The
fish are prepared for examination by killing them with a sharp blow to the
dorsum of the head and exanguination by severing either the causal peduncle or
the spinal cord immediately posterior to the base of the skill. An entire gill
arch is removed and placed into 10% neutral buffered formalin for no longer than
1-2 minutes. It is either examined in toto (small fish only) or a few of the
filaments are removed with scissors, mounted in pH 7.2 phosphate-buffered normal
saline and examined using the 10X and 100X objectives.
If and when a clinical episode of respiratory disease occurs, then an
accurate diagnosis must be made prior to initiating any therapeutic regimen. The
sequence of changes occurring in the gill tissues is the best indicator of the
nature of the causal factors involved. Lesions such as hypertrophy, ECS, and
occlusive hyperplasia all suggest basic physiological upsets which may be
reflected by alterations in other systems. The presence of bacteria and the
so-called gill parasites often is a reflection of an underlying environmental
problem, most common of which is "poor housekeeping."
Once the problem is defined; i.e., the major causal factors identified, the
next step is to "balance" the system. This is best accomplished by,
first, withholding feed for 3-4 days, if the fish are of sufficient size to
permit this. This will (1) reduce the oxygen demand of the fish; (2) reduce the
ammonia-nitrogen generation by the fish and (3) reduce the fecal and uneaten
solids in the system. Second, administer sufficient salt (as granulated NaCl) to
the system to obtain a 1-2% solution. This will (1) reduce the blood
ammonia-nitrogen levels; (2) stimulate mucus secretion; and (3) have an
astringent effect on the gill tissues. Third, reduce the population density to
approximately one-half the oxygen-related carrying capacity of the system. This
should be accomplished without unduly stressing the fish.
If, in addition to the environmental factors being corrected, there are
infectious agents involved, the following treatment regimen has been effective.
First, select a candidate chemotherapeutant which can be administered by water
exposure. Second, conduct a bioassay. The fish to be tested for efficacy and
tolerance to the chemotherapeutant should be obtained from the clinically
affected and "healthy" portions of the affected population. At the end
of the bioassay period - usually an hour for pond conditions, the treated fish
should be examined. If the target organisms were killed or removed from the
gills, the treatment was effective - and safe, if the test fish survived. These
fish should remain under separate conditions for 12-18 hours following the
bioassay to detect any delayed effect.

Expandable Fiberglass Rearing Tanks,
Gemini Fiberglass
Products, 303-278-0033
Gemini fabricates their tanks with hand-laid mat and woven fiberglass which
is approximately 10% stronger than a chopped fiberglass tank. Gemini tanks are
finished with an outside surface of gelcoat, which cosmetically makes for an
improved final product, but more importantly, it eliminates the painful glass
slivers that are often present with chopped fiberglass tanks. For
straight-walled tanks requiring less than  c"
flex and for the extreme stress on transport tanks, Gemini uses a stiffening
method which puts a heavy coat of gelcoat against the glass-smooth mold, than
multiple layers of resin-soaked mat and woven fiberglass cloth which sandwiches
a light-weight layer of balsawood between the surface layers and the back-up
layers of mat and woven fiberglass sealed with a final sprayed layer of gelcoat.
Raceways
These fiberg1ass ba1sawood-Laminated tanks can stand alone without additional
supports. There s no need for external bracing, therefore it s easy to walk and
work between rows. Where space requirements are less demanding and working areas
are more open, fiberglass tanks with bracing offer exceptional rigidity and
strength. With gel-coating on all surfaces, tanks require no painting and very
require low maintenance. Additional options include slots for screens, location
of inlets, drains, standpipes, fish evacuation openings and tank-to-tank
connecting channels with gate valves.
Specialty tanks
Gemini also has specialty tanks of many kinds that will meet your design and
specifications. One-piece or sectional, rectangular, circular or cone-shaped,
sloping or flat bottomed, with or without skirting are all possible.
Panel tanks
With the Gemini panel design, you can have large diameter tanks in varying
widths and depths. These tanks have two bottom pieces and several flanged side
sections and allow for easy access to buildings with limited door openings. An
ideal tank for intensive heavy production, the paneled sides and bottoms nest
together to allow for economical shipping. Nuts, bolts and washers are furnished
with each tank. Also included is either a closed-cell, self adhesive pvc gasket
or the fiberglass materials to seal the seams.
Culture tanks
The round fish culture tanks come in various sizes in sectional or one-piece
design and are available with or without skirting. These tanks have a reinforced
top lip and are gelcoated on inside and outside surfaces. Walls are slightly
tapered to allow nesting together for economy in shipping. Like all Gemini
tanks, a variety of pvc drain fittings, stand pipe assemblies, fish evacuation
portals with gate valves and any other customized needs are easily built into
these tanks.

Fish Disease Treatments
By: FishDoc
The treatment of fish disease is a subject fraught
  with
difficulties and misunderstandings. 
 This is in part due to the need to
oversimplify of what is a complex subject.
In all probability there are as many fish killed, directly or indirectly, by
medications as there are cured. I am sure that we would all agree that
this would be totally unacceptable with any other companion animal. Just imagine
the uproar if cats and dogs routinely died as a result of treatments for fairly
minor ailments.  Clearly, the main reason that other animals fare better is
that they are usually treated by trained professionals, i.e. veterinarians,
whereas fish, by and large, are treated by their owners. There are broadly three
reasons why treatments often fail:
1. An inaccurate diagnosis (or guess) is made as to
the nature of the problem, which in turn results in the wrong treatment being
used. This is often the situation where dartboard medication is
used, whereby, a guess is made as to the nature of the disease (usually based
solely on clinical signs rather than an examination)  and a succession of
different treatments is applied in the hope that one of them will work. This can
often exacerbate an existing condition or mean that the condition simply gets
worse. This really is a kill or cure approach - sadly too often a kill
result. An accurate diagnosis is essential if health problems are to be treated
effectively.
2. An accurate diagnosis is made but the selected
treatment is not successful: Treatments may be unsuccessful for a
variety of reasons. In some cases the germs and bugs (pathogens) are resistant
to a particular treatment. It is not unusual for a treatment that works in one
pond to be less successful against the same parasite in another pond. In such a
situation another appropriate treatment should be used.
Another common problem that affects some disease treatments are variations in
water chemistry. In these situations, water parameters such as hardness, pH or
organic load can interfere with the action of the treatment, rendering it
ineffective. There are also situations, particularly with severe parasite
infestations, where, because of the hosts reactions to their presence, the
parasites are protected by excess mucus.
3. A straightforward treatment overdose:This can arise from a simple miscalculation of dosages, or by the
toxicity of the treatment being affected by water conditions such as pH and
hardness.
A fourth reason stems, I believe, from a misunderstanding of the nature of
many treatments used to combat disease problems. We can divide typical
treatments into two types. First are the proper medications that have been
formulated specifically to fight known pathogens. These would include
antibiotics and other types of veterinary drugs and medicines. These tend to
target the disease-causing organism, and while there may be some side effects,
are unlikely to directly harmful to the patient at the correct doses.
The other class of treatments, and those most likely to be used by the
hobbyist, are not medications in the accepted sense, but chemicals taken
directly from the chemistry lab.  Their action is usually far less
discriminatory. They are usually toxic to all life-forms at relatively low
doses. The effective dose is one that is high enough to kill the smaller
organisms such as parasites, but not high enough to kill larger animals such as
fish. The safety margin is usually very fine. It is important for hobbyists to
appreciate that the majority, including most proprietary treatments, work in
this fashion and that such treatments should not be used in a cavalier fashion.
A further consideration are variations in water chemistry. Most chemicals,
with the exception of salt, are affected to some degree by variances in water
hardness, pH and temperature. Many chemicals also react with dissolved and
particulate organic matter such as fish waste, algae and detritus - thus
affecting or reducing their efficacy.
The three most important
steps are:
An accurate diagnosis.
An accurate dosage calculation.
A follow-up examination to monitor the effectiveness of the treatment.
When applying any treatments
Make sure that the water is well oxygenated
    as many treatments can remove oxygen from the water. This is particularly
    important with any Formalin-based treatments.Turn off any UV lights as the ultraviolet
    radiation may degrade or affect the chemical.Consider whether it is necessary to by pass
    the filter system to avoid adversely affecting the filter biomass. This
    would in turn result in a loss of water quality, which would simply make the
    situation worse.Keep a close eye on fish under treatment as
    even at the correct doses some may react badly. Always be prepared to
    terminate a treatment under such circumstances. Consideration should be made
    as to how a treatment could be rapidly diluted if needed.Many treatments are degraded in strong
    sunlight, particularly potassium permanganate.Consider netting the pond as fish may well
    jump out when treatments are applied.Useful conversions are:
ppm
= mg/litre (i.e.  5 ppm = 5 mg / litre)mg
/ litre  x 3.785 = mg / gall (US)   (i.e  5 mg / litre = 18.9 mg / gall)To
convert imperial gallons to US gallons multiply by 1.2Other
useful figures:1
ounce = 28.35 grams1%
solution =10
  ml per litre10
  gram per litre38
  gram per gal

**Return
to MTAN selection pageReturn to Ashland NFWCO home pageReturn to Region 3 U.S. Fish and Wildlife Service** Product and company
      names mentioned in this publication are for informational purposes only.
      It does not imply endorsement by the MTAN or the U.S. Government.
 Last updated: 
		  November 19, 2008
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