MICROSCOPY RESEARCH AND TECHNIQUE 58:481– 487 (2002)

The Physiology of Flatfish Chromatophores
DEREK BURTON*
Department of Biology and Ocean Sciences Centre, Memorial University of Newfoundland, St. John’s,
Newfoundland, Canada A1B 3X9

KEY WORDS

pleuronectiformes; integumentary patterning; melanophores; xanthophores;
iridophores

ABSTRACT
Most flatfish, of the order Pleuronectiformes, possess a white lower side, and abrown or grey upper side. This upper side can display integumentary patterning with dark areasand colored or white spots. Chromatophores in flatfish are dermal and epidermal melanophores, aswell as dermal xanthophores, erythrophores, iridophores, and leucophores, combinations of which
contribute to the color and patterning. Cellular studies demonstrate pattern-related differences innumerical distribution between the types of chromatophores, and in their size, both of which will
enhance contrast between areas of the pattern. As well as these morphological characteristics, there
are also clear physiological differences, with melanophores from various areas of the patterns
demonstrating differential responsiveness to background and to stress/excitement stimuli. Regulation of flatfish melanophore responses is predominantly neural, through the sympathetic nervous
system; the pituitary hormones in these fish function in maintaining final equilibria in physiological adaptations to backgrounds. Melanophores from main components of patterns also responddifferently in vitro to electrical stimulation, to pituitary hormones, and to sympathomimetic drugs
and their antagonists. Sensitivity characteristics with ␣- and ␤-adrenergic pharmacological reagents invitro indicate the existence of a pattern-related balance in ␣- and ␤-adrenoceptor mediation in melanophore regulation. The patterning mechanism is complex, with both morphological and physiologicaldifferences at the chromatophore level, as well as involvement of central processing and control, which
remains to be analysed. Microsc. Res. Tech. 58:481– 487, 2002. © 2002 Wiley-Liss, Inc.
INTRODUCTION
Within the diverse range of chromatic biology displayed by teleost fish, that of flatfish, of the order
Pleuronectiformes (Heterosomata), has received muchattention from biologists for more than a hundredyears. This interest has focused largely on the regulation of a complex patterning behavior, its most likelyrole being concealment, which has heightened importance in flat-bodied fish with a demersal habit. After
metamorphosis, most pleuronectiform flatfish have apale lower blind side and a dark upper ocular side. This
upper side has patterns with dark patches, spots, orbands, and white and colored spots, which are morphological entities (Hewer, 1926; Lanzing, 1977; Osborn,1939), which vary in form between species. The rangeof terminology employed by various authors for themarkings on different species has recently been reviewed (Healey, 1999).
The physiology of teleost melanophores encompasses
both short-term melanosome motile responses, classically known as “physiological” color change (Bagnara
and Hadley, 1973), and long-term changes in theamount of melanin, referred to as “morphological” color
change (Bagnara and Hadley, 1973). Both types of response to background involve regulatory factors suchas hormones, neurotransmitters, and paracrine agents.
The control of short-term physiological responses involves both rapid sympathetic nervous (Pouchet, 1876;
von Frisch, 1911), with noradrenaline as neurotransmitter (Fujii, 1961), and slower hormonal (Hewer,
1926; Spaeth, 1913) mechanisms. Recent research©

2002 WILEY-LISS, INC.

(Baker et al., 1986; Sugimoto et al., 2000) has demonstrated that the same regulatory factors can have roles
in both melanosome motile responses and changes inmelanophore density in teleosts.
Studies on the regulation of flatfish patterning havemainly concentrated on the short-term motile responses of the chromatophores. Healey (1999) has
grouped such investigations into those that concentrate on differential reactions of major components ofthe patterns to homogeneous black and white backgrounds (Burton, 1975, 1981; Burton et al., 1995;
Hewer, 1926, 1931; Kuntz, 1915; Osborn, 1939; Polimanti, 1912), and into those that describe overall patterning in response to fine or coarse divisions of lightand dark areas in their background, or to gradations ofgrey (Healey, 1999; Mast, 1914; Sumner, 1911). The
two approaches are complementary: differential responsiveness of major pattern components providing aworking model for experimental analysis of the physiological regulatory mechanisms involved, whole pattern analyses providing a basis for chromatic behavior
studies.

*Correspondence to: Derek Burton, Department of Biology and Ocean Sciences
Centre, Memorial University of Newfoundland, St. John’s, Newfoundland, Canada A1B 3X9
Received 26 November 2001; accepted in revised form 12 January 2002
Grant sponsor: Natural Sciences and Engineering Research Council of Canada.
DOI 10.1002/jemt.10166
Published online in Wiley InterScience (www.interscience.wiley.com).

482

D. BURTON

The relative roles of the density and physiologicalcontrol of melanophores in flatfish pattern-related responses to background has been the subject of a classical debate. Based on macroscopic observations, Sumner (1911) proposed that patterning is a differential
reaction, determined by the distribution of efferent
nerve fibers, rather than depending on synchronizedresponses of chromatophores differing in size and numbers. Hogben (1924) was opposed to this view, claimingthat flatfish patterning was dependent on differencesin the numerical distribution of chromatophores.
Hewer (1926) interpreted independence of white spot
melanophore responses in Limanda limanda as evidence for central control of differential responsiveness,rather than its representing a function of the chromatophores and substances directly affecting them.
Lanzing (1977) and Douglas and Lanzing (1981) suggested that flatfish patterning responses might be an
expression of combinations of a limited number of preset internal patterns. Healey (1999) considered that, ingeneral, responses of Pleuronectes platessa to gradedbackgrounds do not support Lanzing’s suggestion, stating that on current knowledge, any conclusions about
the existence of preset internal patterns in flatfish
would be premature. The coarseness or fineness of flatfish patterns can be influenced by the degree of subdivision of the background into black and white squares,
although the fish do not reproduce the actual form of
the background (Healey, 1999; Mast, 1914; Sumner,
1911). P. platessa responds differently to graded, quantitatively defined, plain grey backgrounds, and to thosethat are black/white patterned, although in both responses pattern components become prominent or hidden in a hierarchical order (Healey, 1999). Separate
stimulation of the two eyes, by coarse and fine backgrounds (Mast, 1914), produces patterns of intermediate texture, indicating an absence of direct specificneural connections between retinal cells and skin chromatophores. However, stimulation of an area of theupper retina is necessary for patterning responses inthe skin in Solea solea (de Groot et al., 1969).
Many of the studies on flatfish patterning have been
macroscopic, but increasing use of microscopic analyses, with in vivo and in vitro experimentation, has
improved understanding of its cellular basis considerably. It has become progressively clear that variations
in color within the patterns are the result of interactions between the relative motile responsiveness andthe relative densities of the different types of chromatophores. Both aspects will be discussed in this review, in
relation to the regulatory processes involved.
TYPES OF CHROMATOPHORES IN
FLATFISH AND THEIR PATTERNRELATED DENSITIESThe pale side of flatfish possesses abundant iridophores; the dark side bearing melanophores, xanthophores, erythrophores, and iridophores (Cunningham and McMunn, 1893). Chromatophores are usuallydermal, but in at least some species of flatfish, large
numbers of epidermal melanophores also occur (Burton, 1979, 1980; Hewer, 1926; ). There are two theories
on the origin of epidermal melanophores (Hewer,1926): either they arise by outward migration of dermal melanophores, or they arise de novo from epider-mal cells. Unlike the stellate dermal melanophores, thefine dendritic shape of those in the epidermis is
adapted to being between tightly compressed cells. In
Pseudopleuronectes americanus, epidermal melanophores form a mid-epithelial layer and are morphologically similar to those of amphibia (Bagnara and Hadley, 1973). Ultrastructural studies (Burton and
Hatcher, unpublished data) reveal that they are nucleated, with their pigments organized into melanosomes.
There are reports (Stoumboudi et al., 2001) that they
represent degenerating dermal melanophores in someteleosts, and there is speculation that this may be so inflatfish (Kuntz, 1915; Hewer, 1926). In P. americanus
iridophores contain elongated guanin crystals (Burtonand Hatcher, unpublished data), but in P. platessa,
leucophores, containing small moveable guanin particles, also occur (Ahmad, 1979).
The chromatophore types can display variation in
their numerical distribution within flatfish patterns. In
the case of P.americanus, the pattern includes threemajor components (Burton, 1979; Osborn, 1939), which
are displayed during responses to black and whitebackgrounds (Fig. 1), and contribute to the disruptive
patterning on stony backgrounds (Burton, 1979). These
contrasting areas consist of a dark-band component,with four dark bands (two across the mid-body, one
around the operculum, and one across the caudal peduncle), a white spot component, and a general background component. This last component represents ageneral grey background, which may have a complex
mottling, but against which the dark bands and whitespots can contrast sharply.
Within these major components, inverse numerical
relationships occur between melanophores and xanthophores compared with the iridophores (Burton,1980). This is particularly pronounced for epidermalmelanophores, with large numbers in the dark bands
compared with the white spots (Fig. 2), and for iridophores with large numbers in the white spots compared with the dark areas. Measurements of the diameter of the intracellular aggregated or dispersed pigment mass (Mayo and Burton, 1998a) demonstratethat dermal melanophores from dark areas are larger
than those from white spots. Such pattern-related gradients in numerical distribution and size will enhancecontrast during differential physiological responses.
In telesosts, melanophore morphological changes in
response to long-term background exposure can be extensive, involving pituitary and neural regulatory factors associated with physiological color change. Prolonged administration of ␣-MSH (melanophore-stimulating hormone) induces increases in dermalmelanophore density in the tilapia, Oreochromis
mossambicus (formerly Sarotherodon mossambicus)(van Eys and Peters, 1981). MCH (melanin-concentrating hormone) inhibits MSH secretion and reduces melanogenesis in black-adapted rainbow trout, Salmo
gairdneri, now Oncorhynchus mykiss, (Baker et al.,1986). Apoptosis, thought to be involved in density
decrease during long-term adaptation to white in the
medaka, Oryzias latipes (Sugimoto et al., 2000), is suppressed by denervation and stimulated in vitro by noradrenaline, but not by MCH. In contrast with otherteleosts, little capacity for changes in melanophoredensity has been observed in adult flatfish. SuchPLEURONECTIFORM INTEGUMENTARY PATTERNING

483

Fig. 1. Winter flounder, Pseudopleuronectes americanus (length 29 cm) displaying integumentary
patterning during paling, 2 min after background change from black to white. The pattern includes threemajor pattern components: D, one of the bands of the dark band component; W, one of the spots of thewhite spot component; G, the general background component.

Japanese flounder can be enhanced by MSH (Matsumoto and Seikai, 1992), although initiated by theirown “built-in clock.” In adult flatfish, integumentaryfactors regulating melanogenesis may be equal to, or
more important than the pituitary. A melanogenesis
stimulating factor (MSF) and a melanogenesis inhibiting factor (MIF), locally distributed in the skin, could
be important in establishing pigmentary patterns invertebrates generally (Bagnara et al., 1992).

Fig. 2. Numerical distribution of chromatophores within the major
pattern components (dark bands, white spot and general backgroundcomponents) of winter flounder, Pseudopleuronectes americanus(based on data from Burton, 1980). E, epidermal melanophores; D,dermal melanophores; I, iridophores; X, xanthophores. Mean values ⫾SEM for 6 flounders (5 samples per fish).

changes in response to background or MSH are limited
to epidermal melanophore numbers (Burton, 1993;
Hewer, 1926). However, melanophore differentiation invitro from dissociated embryonic neural crest cells of

CHROMATOPHORE RESPONSIVENESS IN
FLATFISH PATTERN DISPLAY
In this laboratory, chromatophore responsivenesswithin the major pattern components in P.americanus
has been analysed microscopically (Burton, 1979,1980). After white to black background change, melanosome dispersion is rapid in dark-band melanophores
compared with in the general background component.
Following transfer from black to white, melanosomes
aggregate more rapidly in general background component melanophores than in the dark bands. Aggregation of melanosomes in melanophores in the whitespots “unmasks” the dense areas of iridophores to display an extreme pallor. Responses of white spot melanophores are not solely background related; paling followed by darkening of these spots can occur very rapidly in dark flounder adapted to a back background. De
Groot et al. (1969) state that it is not known whatreleases a display of pleuronectid white spots, although
excitement may affect their prominence (Osborn,1939). Also, in response to excitement, dark band mela-

484

D. BURTON

Fig. 3. Comparison of the effectof chromatic decentralization on
the paling responses of winterflounder,Pseudopleuronectes
americanus (solid line), and theEuropean minnow, Phoxinus laevis (aggregate) (dashed line), after
transfer from a black backgroundto white. Operated fish (solid circles), controls (open circles). The
graphs for minnow are adaptedfrom Healey (1951) and for winterflounder from Burton (1981) for
dermal melanophores of the general background component of thepattern. The melanophore index isadapted from Hogben and Slome(1931) in which 1.0 represents
complete pigment aggregation and
5.0 complete dispersion.

nophores can display rapid partial dispersion of theirmelanosomes in white-adapted pale flounder (Burton,1979). This microscopic analysis has clearly demonstrated that the pattern-related differences in responsiveness are not solely the product of the type of melanophore numerical differences summarized in Figure
2, but also represent physiological differences. Less isknown about the other chromatophores, but xanthophore pigments disperse rapidly on black backgrounds and aggregate slowly on white (Burton, 1980),
their chromatic interaction with the melanophores
causing cream, yellow, and olive hues during paling.
No chromatic activity has been observed in flatfish
iridophores.
Flatfish can display pronounced in vivo facilitation ofcolor changes and melanophore responses to background change (Burton and O’Driscoll, 1992; Mast,
1914; Osborn, 1939; Sumner, 1911), and to noradrenaline injections (Burton and O’Driscoll, 1992), withfaster responses to repeat trials. Such facilitation mustbe factored into experimental design. This attribute
will have adaptive significance related to the degrees ofbackground change experienced during movements
within habitats. During responses to black and whitebackground changes, epidermal melanophores also display a complete range of responses (Burton, 1979,
1980, 1981), with a capacity for facilitation (Burton andO’Driscoll, 1992), i.e., they are fully functional.
CONTROL OF CHROMATOPHORES IN
FLATFISH PATTERN DISPLAY
Compared with some other teleosts, control of melanosome aggregation in flatfish is primarily neural. Experiments on turbot (Pouchet, 1876) first establishedsympathetic nervous control of melanosome aggregation in teleosts, including flatfish. Neural surgical section, electrical stimulation, and pharmacological exper-

iments (Burton, 1981; Fernando and Grove, 1974a;
Hewer, 1926; Osborn, 1939; Scott, 1965) have demonstrated that the flatfish pigmento-motor neural pathway has a spinal outflow that is more anterior than in
Phoxinus (von Frisch, 1911), at the sixth vertebra (Burton, 1981; Fernando and Grove, 1974a; Hewer, 1926)
rather than the fifteenth. Chromatic decentralizationin P. americanus, by spinal section anterior to the sixth
vertebra, produces a dark upper surface, none of thepattern components paling on exposure to a whitebackground for prolonged periods (Burton, 1981). Thisrefractoriness contrasts with the capacity of Phoxinus
to pale slowly, and almost completely on a white background, after similar surgery (Fig. 3), and to darken
again slowly on black (Healey, 1951). Hypophysectomy
does not affect melanophore responses of any of thepattern components of P. americanus to black andwhite backgrounds (Burton, 1981), whereas in hypophysectomized Phoxinus (Healey, 1948) melanophore responses on both backgrounds are attenuated. Overall,these observations demonstrate that the pituitary has
little or no role in melanosome aggregation and dispersion processes in P.americanus, in contrast with Phoxinus. Unlike the melanophores, the xanthophores of P.
americanus are greatly affected by hypophysectomy,
their pigment aggregating. Injection with crude pituitary extract, or with MSH, can produce xanthophore
pigment dispersion and a hyperxanthic coloration(Burton, 1981). Melanophores of different flatfish species are refractory to in vivo treatment with MSH (Burton, 1981; Osborn, 1939; Scott, 1965). Also the plasmatic ␣-MSH level in P. flesus is low and does not varyduring 18 days adaptation to black and white backgrounds (Baker et al., 1984), which differs fromchanges in such levels in Salmo gairdneri and Anguillaanguilla (Baker et al., 1984). Crude pituitary extracts
can produce an MCH effect on melanophores of P.

PLEURONECTIFORM INTEGUMENTARY PATTERNING

americanus, but no data are available for plasmaticlevels of this hormone.
Work in this laboratory has also included in vitro
experiments with pituitary hormones. In contrast to
the in vivo refractoriness, in vitro incubations of scale
slips (a scale bearing a small skin sample) with ␣-MSH
and MCH can produce melanosome dispersion and aggregation, respectively, in melanophores from P.
americanus (Burton and Vokey, 2000a). In such incubations, melanosomes, aggregated initially with MCH,
disperse in increasing concentrations of ␣-MSH added
to the MCH vehicle (Burton and Vokey, 2000a). Melanosomes, dispersed initially with ␣-MSH, aggregate inincreasing concentrations of MCH added to the ␣-MSH
vehicle (Burton and Vokey 2000a). These experiments
demonstrate the presence of receptors for these two
pituitary hormones in this species. In vivo, neural control dominates in flatfish, more than in Phoxinus, over
pituitary control. It is deduced from the effects of hypophysectomy and chromatic decentralization thatplasmatic concentrations of MSH and MCH in flatfish,
unlike in some other teleosts, must be inadequate toregulate melanosome movements in the slow attainment of final equilibria, but will function in maintaining them. Such neural dominance is consistent withthe degree of importance of patterning in flatfish, with
its finely controlled differential responses. However,there are pattern-related differences in sensitivity to
MSH and MCH in vitro (Burton and Vokey 2000a),which could influence threshold levels in responses toneural stimuli.
Flatfish scale slips also provide a useful neuro-effector model for isolating melanophores, with their nerve
terminals, from the major pattern components for use
in microscopic in vitro experimentation. However, it isessential to standardize the background color of theflatfish from which scale slips are sampled, since thisfactor can greatly influence in vitro responsiveness ofmelanophores (Burton and Everard, 1989). Also, stimulus repetition in vitro can enhance responsiveness(Burton and Everard, 1991), which must be taken into
account in experimental design. Although response
rates in vitro can be faster than in vivo, pattern-relateddifferences are not as pronounced as those that involve
both central processing and peripheral neuro-effector
components (Burton and Snow, 1993). Responses to in
vitro electrical stimulation depend on functioning
nerve terminals; scale slip melanophores will not respond to such stimuli, but retain sensitivity to exogenous noradrenaline, after chemical sympathectomy
with 6-hydroxydopamine, demonstrating that theirplasma membrane is not electrically excitable (Mayoand Burton, 1998a). With intact scale slips, squarewave pulses with a duration of 2 ms evoke complete
aggregation of melanosomes in dermal melanophores(Mayo and Burton, 1998a), the frequencies and minimal voltages across the electrodes differing for scale
slips from the general background component (10 Hz,
26 v), dark bands (2 Hz, 52 v), and white spots (10 Hz,
36 v). These electrophysiological characteristics indicate that there are probably neuronal differences associated with the pattern that require further study. No
electrical stimulation parameters could be establishedthat would evoke epidermal melanophore responses,
indicating an absence of a close neuro-anatomical rela-

485

tionship, which is also supported by ultrastructural
studies (Burton and Hatcher, unpublished data). A K⫹rich incubation medium (aggregating fluid) depolarizes
teleost scale-slip nerve terminals, releasing their neurotransmitter, and aggregating melanosomes (Fujii,1959). Compared with the response to electrical stimulation, that with K⫹ is slower (Mayo and Burton,
1998a), but there is complete aggregation of melanosomes in the epidermal melanophores. A neurotransmitter field effect would explain both this responsewith K⫹ and the slower response of epidermal melanophores in vivo. With scale slips from P.americanus,
white spot melanophores respond most rapidly to K⫹ ,whilst those from dark bands are the slowest (Burton
and Snow, 1993). Following K⫹-induced melanosome
aggregation, subsequent incubation in balanced salt
solution, with its higher Na⫹ concentration, disperses
the melanosomes again (Burton and Snow, 1993). The
rate of such dispersion is fastest in melanophores fromwhite spots and slowest in those from the general background component.
Fujii and Oshima (1986) have reviewed pharmacological evidence demonstrating ␣- and ␤-adrenoceptor
involvement in melanophore responses of various teleosts. Burton and associated workers have investigated these responses in relation to the differential
responsiveness of P.americanus. The direction of melanophore responses, in vitro, to noradrenaline is concentration-related in P. americanus, melanosomes aggregating with ⬎10-8M and their dispersion in balanced salt solution enhanced with ⱕ10-8 M.
Melanosome aggregation in response to high concentrations (⬎10-8M) of noradrenaline (Burton et al., 1995)
is mediated through ␣-adrenoceptors, which can beblocked by phentolamine (Burton et al., 1995). Concentration-response data for noradrenaline ⬎10-8M indicate that white spot melanophores are the least sensitive, with a high concentration threshold, comparedwith the other two pattern components that show nodifference (Vokey and Burton, 1998). Noradrenaline
response rates are the fastest for the white spot melanophores and slowest for those from dark bands (Vokey
and Burton, 1998). Phentolamine also inhibits responses to electrical stimulation and to K⫹ indicating
melanophore ␣-adrenoceptor mediation (Mayo andBurton, 1998a). With both types of neuronal stimulation, the white spot melanophore responses are themost sensitive to phentolamine, and those of the general background melanophores the least sensitive(Mayo and Burton, 1998a). The ␣1- and ␣2-adrenergic
agonists phenylephrine and clonidine evoke aggregation (Burton and Vokey, 2000b). However differences in
the potency of these agonists, and of the ␣1- and ␣2adrenergic antagonists prazosin and yohimbine, indicate a pattern-related balance between the ␣1 and ␣2
subtypes on the melanophores, although the ␣2 -subtype is predominant in each major pattern component(Burton and Vokey, 2000b). As with noradrenaline,
white spot melanophores are the least sensitive to bothphenylephrine and clonidine. Aggregation in responseto electrical stimulation is also inhibited by prazosin
and yohimbine, the latter being more potent (Mayo andBurton, 1998a).
Low concentrations (ⱕ10-8M) of noradrenaline, andof the ␤-adrenoceptor agonist isoproterenol, enhance

486

D. BURTON

the rate of pigment dispersion in melanophores fromeach pattern component during in vitro incubation inbalanced salt solution (Mayo and Burton, 1998b). The
␤-adrenoceptor antagonist propranolol can inhibit thisenhancement of dispersion (Mayo and Burton, 1998b).
The ␤2-adrenoceptor agonist terbutaline can reverse
the aggregating effects of noradrenaline and electricalstimulation to evoke pigment dispersion (Mayo andBurton, 1998b) . There is preliminary evidence that the␤1 agonist, dobutamine, can enhance the dispersion
rate in balanced salt solution (Burton, unpublisheddata). ␤-adrenoceptors have not been studied as intensively as the ␣-subtype in flatfish pattern regulation,
but the data available do indicate pattern-related differences in sensitivity to ␤-adrenergic agonists andantagonists. In particular, melanosomes of dark band
melanophores disperse most readily, and those of thegeneral background least, when electrically stimulated
aggregation is reversed by increasing concentrations ofthe ␤2- adrenergic agonist terbutaline (Mayo and Burton, 1998b).
The melanophore sensitivities to ␣- and ␤-adrenergic
pharmacological reagents in vitro indicate that a pattern-related balance exists between ␣- and ␤-adrenoceptor mediation, which represents a further important component in the patterning regulation (Mayo andBurton, 1998a). Although white spot melanophores
demonstrate the most rapid aggregation rate in response to K⫹ ions and noradrenaline, they also havethe highest concentration thresholds with noradrenaline and ␣-adrenoceptor agonists. The melanophores of
the white spots and dark bands, which display excitement responses counter to background-related responses, may have additional regulatory factors andreceptors (Vokey and Burton, 1998). Such regulatory
factors could include a separate innervation (Hewer,1926) for the white spots, in addition to that from thecentral processing and pigmento-motor neural pathway for background-related paling.
There is no evidence for acetycholine mediation inpigment dispersion in flatfish (Fernando and Grove,
1974b; Scott, 1965), or for purinergic involvement, as
described for some other teleosts (Fujii and Oshima,1986). In teleosts, a sympathetic component of the autonomic nervous system is more clearly defined than aparasympathetic. A single neurone type regulating
melanosome bi-directional movements, in response todifferent concentrations of a single neurotransmitter,
represents a functional alternative to adrenergic andcholinergic antagonism at this phylogenetic level.
CONCLUSIONS AND FUTURE DIRECTIONSThis review demonstrates the complex basis of patterning in flatfish, emphasizing how morphological andphysiological components are interdependent in theirdisplay, involving both differential responsiveness andrelative densities of chromatophores. This combination
provides a potential for a wide range of graded responses, without necessarily implicating the existenceof a limited number of preset internal patterns in flatfish. So far, attention has concentrated on peripheral
neuroeffector considerations. There have been no experimental, or anatomical, studies to ascertain how
many brain centers are involved in the regulation of
flatfish patterns in response to background and excite-

ment stimuli. At the effector level, interest has been
focused on the roles of catecholamines, pituitary hormones, and differences in melanophore receptor mediation. The regulation of the other chromatophores warrants more study. It is not known whether other regulatory factors, such as modulatory neuropeptides, areinvolved in differential responsiveness within flatfish
patterns. Morphologically, the possible involvement of
MSF and MIF in regulating morphogenesis of flatfish
patterns invites investigation. Although considerable
progress has been made towards an understanding of
the unique patterning processes of flatfish, there areclearly extremely interesting challenges to be addressed in this field in the future.
ACKNOWLEDGMENTS
This review is dedicated to the late Dr. E.G. (Tim)
Healey, whose research clarified neural and hormonal
relationships in melanophore control in teleost fish,
and who introduced me to the field of fish colourchange. I am grateful to Trevor Avery and Graham
Hillier for assistance with graphics work, Peggy-Ann
Parsons for typing the manuscript, and Dr. Margaret
Burton for assistance in its final preparation.
REFERENCES
Ahmad E. 1979. The integumentary chromatophore patterns in theplaice Pleuronectes platessa L., with special reference to their responses towards different variegated backgrounds. Ph.D. thesis,
London University.
Bagnara JT, Hadley ME. 1973. Chromatophores and color changes:
the comparative physiology of animal pigmentation. Englewood
Cliffs, NJ: Prentice Hall, p 6 –16.
Bagnara JT, Fukuzawa T, Johnson WC, Law JH, Samaraweera P,
Zuasti A. 1992. Integumental pigmentary factors of lower
vertebrates: models for human hypo- and hypermelanoses. Pigm
Cell Res (Suppl) 2:254 –261.
Baker BI, Wilson JF, Bowley TJ. 1984. Changes in pituitary andplasma levels of MSH in teleosts during physiological colourchange. Gen Comp Endocrinol 55:142–149.
Baker BI , Bird DJ, Buckingham JC. 1986. Effects of chronic administration of melanin- concentrating hormone on corticotrophin,melanotrophin and pigmentation in the trout. Gen Comp Endocrinol 63:62– 69.
Burton D. 1975. The integumentary melanophore patterns of two
teleost species Gasterosteus aculeatus and Pseudopleuronectes
americanus. Can J Zool 53:507–515.
Burton D. 1979. Differential chromatic activity of melanophores in
integumentary patterns of winter flounder (Pseudopleuronectes
americanus Walbaum). Can J Zool 57:650 – 657.
Burton D. 1980. A cellular analysis of chromatophore patterning in
winter flounder (Pseudopleuronectes americanus Walbaum). Comp
Biochem Physiol A67:453– 457.
Burton D. 1981. Physiological responses of melanophores and xanthophores of hypophysectomized and spinal winter flounder, Pseudopleuronectes americanus Walbaum. Proc R Soc Lond B213:217–
231.
Burton D. 1993. The effects of background colouration and ␣-MSH
treatment on melanophore frequency in winter flounder, Pleuronectes americanus. J Comp Physiol A173:329 –333.
Burton D, Everard B. 1989. An effect of in vivo chromatic adaptation
on melanophore in vitro sensitivity. Comp Biochem Physiol 93C:
313–316.
Burton D, Everard B. 1991. Melanophore response enhancement during in vitro K⫹ and Na⫹ stimulus repetition in Pseudopleuronectes
americanus. Comp Biochem Physiol 98A:413– 416.
Burton D, O’Driscoll MP. 1992. Facilitation of melanophore responses
in winter flounder Pseudopleuronectes americanus. J Exp Biol 168:
289 –299.
Burton D, Snow A. 1993. An in vivo and in vitro comparison ofdifferential melanophore responsiveness in flatfish integumentarycolour patterns. Zool Sci 10:577-585.
Burton D, Vokey JE. 2000a. The relative in vitro responsiveness ofmelanophores of winter flounder to ␣-MSH and MCH. J Fish Biol
56:1192–1200.

PLEURONECTIFORM INTEGUMENTARY PATTERNING
Burton D, Vokey JE. 2000b. ␣1- and ␣2- adrenoceptor mediation inmelanosome aggregation in cryptic patterning of Pleuronectes
americanus. Comp Biochem Physiol 125A:359 –365.
Burton D, Vokey J, Mayo D. 1995. Adrenoceptors in cryptic patterningof a flatfish, Pleuronectes americanus. Proc R Soc Lond B261:181–
186.
Cunningham JT, McMunn CA. 1893. On the colouration of the skinsof fishes, especially of pleuronectidae. Phil Trans R Soc Lond B184:
765– 812.
de Groot SJ, Norde R, Verheizen FJ. 1969. Retinal stimulation andpattern formation in the common sole Solea solea (L) (Pisces: Soleidae). Neth J Sea Res 4:339 –349.
Douglas WA, Lanzing WJR. 1981. Colour change and visual cues inthe sand flathead, Platycephalus arenarius (Ramsey and Ogilby). J
Fish Biol 18:619 – 628.
Fernando MM, Grove DJ. 1974a. Melanophore aggregation in theplaice (Pleuronectes platessa L.). I. Changes in in vivo sensitivity tosympathomimetic amines. Comp Biochem Physiol A48:711–721.
Fernando MM, Grove DJ. 1974b. Melanophore aggregation in theplaice (Pleuronectes platessa L.). II. In vitro effects of adrenergic
drugs. Comp Biochem Physiol A48:723– 732.
Fujii R. 1959. Mechanisms of ionic action in the melanophore systemof fish.-1. Melanophore-concentrating action of potsassium andsome other ions. Annot Zool Jpn 32:47–58.
Fujii R. 1961. Demonstration of the adrenergic nature of transmission
at the junction between melanophore-concentrating nerve and nelanophore in bony fish. J Fac Sci Univ Tokyo Section IV 9:171–196.
Fujii R Oshima N. 1986. Control of chromatophore movements inteleost fishes. Zool Sci 3:13– 47.
Healey EG. 1948. The colour change of the minnow (Phoxinus laevis
Ag). Bull Anim Behav 6:5–15.
Healey EG. 1951. The colour change of the minnow (Phoxinus laevisAg.). I. Effects of spinal section between vertebrae 5 and 12 on the
response of the melanophores. J Exp Biol 28:297–319.
Healey EG. 1999. The skin pattern of young plaice and its rapid
modification in response to graded changes in background tint andpattern. J Fish Biol 55:937–971.
Hewer HR. 1926. Studies on the colour changes of fish. II. An analysisof the colour patterns of the dab. III. The action of nicotine andadrenalin in the dab. IV. The action of caffeine in the dab, and atheory of the control of colour changes in fish. Phil Trans R Soc Lond
B215:177–200.
Hewer HR. 1931. Studies on the colour changes in fish. V. The colour
patterns in certain flat- fish and their relation to the environment.
J Linn Soc Lond Zool 37:493–513.
Hogben LT. 1924. The pigmentary effector system. Biol Mon Man
Edinburgh 1:93–120.
Hogben LT, Slome D. 1931. The pigmentary system. VI. The dual
character of the endocrine coordination in amphibian colour change.
Proc R Soc Lond B108:10 –53.

487

Kuntz A. 1915. The histological basis of adaptive shades and colours
in the flounder Paralichthys albiguttus. Bull US Bur Fish 35:1–29.
Lanzing WJR. 1977. Reassessment of chromatophore regulation in
two species of flatfish (Scophthalmus maximus and Pleuronectes
platessa). Neth J Sea Res 11:213–222.
Mast SO. 1914. Changes in shade, color, and pattern in fishes, andtheir bearing on the problems of adaptation and behaviour, withespecial reference to the flounders Paralichthys and Ancylopsetta.
Bull US Bur Fish 34:177–238.
Matsumoto J, Seikai T. 1992. Asymmetric pigmentation and pigment
disorders in pleuronectiformes (Flounder). Pigm Cell Res Suppl
2:275–282.
Mayo DJ, Burton D. 1998a. The in vitro physiology of melanophores
associated with integumentary patterns in winter flounder (Pleuronectes americanus). Comp Biochem Physiol A121:241–247.
Mayo DJ, Burton D. 1998b. ␤2-Adrenoceptors mediate melanosome
dispersion in winter flounder (Pleuronectes americanus). Can J Zool
76:175–180.
Osborn CM. 1939. The physiology of colour changes in flatfishes. J
Exp Zool 81:479 –515.
Polimanti O. 1912. Einfluss der Augen and der Bodenbeschaffenheit
aut die Farbe der Pleuronektiden. Biol Z 32:296 –307.
Pouchet G. 1876. Des changements de coloration sous l’influence desnerfs. J Anat Physiol Paris 12:1–90, 199 –223.
Scott GT. 1965. Physiology and pharmacology of color change in thesand flounder, Scopthalmus aquosus. Limnol Oceanogr 10:R230 –246.
Spaeth RA. 1913. The physiology of chromatophores of fishes. J Exp
Zool 15:527–585.
Stoumboudi MT, Abraham M, Wendelaar BSE, Iger Y, Tsangavis K,
van Ham E, and Alexis M. 2001. Ammonia induces stress-related
histological changes in the skin of cultured gilthead seabream.
Abstracts p. 31, 10th European Congress of Ichthyology at Prague,
Czech Republic, September, 3–7, 2001.
Sugimoto M, Uchida N, Hatayama M. 2000. Apoptosis in skin pigment cells of the medaka, Oryzias latipes (Teleostei), during longterm chromatic adaptation: the role of sympathetic innervation.
Cell tissue Res 301:205–216.
Sumner FB. 1911. The adjustment of flatfishes to various backgrounds. A study of adaptive color change. J Exp Zool 10:409 –505.
van Eys GIJM, Peters PTW. 1981. Evidence of a direct role of ␣-MSH
in morphological background adaptation of the skin in Sarotherodon mossambicus. Cell Tiss Res 217:361– 372.
Vokey JE, Burton D. 1998. Sensitivity of winter flounder melanophores after removal of the epidermis from in vitro preparations. J
Fish Biol 53:695–700.
von Frisch K. 1911. Beiträge zur Physiologie der Pigmentzellen in derFischhaut. Pflüg Arch Physiol 138:319 –387.