COLORATION IN FISHES: its Regulation and significance.

Presented by:GAZEE OWAIS YOUSUF15ZYM 21M.Sc. (F)ALIGARH MUSLIM UNIVERSITY

Animal coloration is the general appearance of an animal resulting from the reception or emission of light from its surface.

Coloration depends upon two important factors; the color and distribution of organism’s biochromes, quality and quantity of light falling on the organism.

There are several separate reasons why animals have evolved colors: Environmental changes, Camouflage, disease, signaling, advertising, during life as well as mood etc.

INTRODUCTION

HISTORY : Colouration of fishes is due to the

presence of various kinds of pigments in the integuments.

ARISTOTLE mentioned the ability of the octopus to change colour for both camouflage and signalling in his Historia animalium in 400 BC.

CHARLES DARWIN described the colour change ability of cattle fish in the voyage of the beagle in 1860

COLORATION in fishes is primarily due to skin pigments in the integuments, their rearrangement causes some species to exhibit bright colors while others show uniform shade.

In many species the general coloration, and particularly the characterstic marking is in the form of bars, stripes, spots and blotches.

These marks are remarkably constant in all individuals of a particular species but some others have a good deal of difference.

Pigment cells are defined as cellular systems that effect coloration of the skin.

The chromatophores are found in the dermis layer of skin.

They have pigment containing intracellular bodies called chromatosomes.

CHROMATOPHORES

Fishes have only four biochromes, varied color patterns are obtained by mixing of these exisisting pigments in variable proportions.

Melanophores, Erythophores, and Xanthophores are called the light absorbing chromatophores.

Iridiophores are called as the light reflecting chromatophores.

CHROMATOPHORES (Contd.)

CHROMATOPHORES PIGMENTS SOURCE COLOR

Melanophores Melanin Diet Black/Brown

Erythophores Carotenoids Diet Red/orange

Xanthophores Carotenoids Diet Yellow

Iridiophores Guanine Diet White

CLASSIFICATION OF CHROMATOPHORES

CHROMATOPHORES RESPONSE

PHYSIOLOGICAL RESPONSE:(neural and hormonal)Redistribution of pigment organelles within the boundary of the cell.

MORPHOLOGICAL RESPONSE: Involves increase or decrease in number of pigment cells or the amount of pigment they contain.

REGULATIONTwo types of regulatory mechanismsI. Neural regulation II. Hormonal regulation

Neurons produce chemical Messengers called Neuro- hormones Which activates the chromatophores.

Migration of pigments is under the control of pituitary glandIt have been suggested that it’s the hypothalamus that produces these hormones and are then stored in pituitary gland, e.g., MSH (MELANOPHORE STIMULATING HORMONE)

In some fishes colour change is under both neural and hormonal control, e.g., Anguilla anguilla ,Fundulus etc.

SIGNIFICANCE OF COLOR CHANGE IN FISHESPatterns of coloration and ability of the fish to change it, helps the fishes in various ways such as:

CONCEALMENT

DISGUISE

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CONCEALMENTIt provides protection to fish by concealment from the enemy (camouflage).

Various kinds of concealing colors method are suggested:

Obliterative colorationVariable color resemblanceDisruptive coloration

OBLITERATIVE SHADING

This type of concealing coloration depens upon counter shading.

The dorsal surface of fish appears dark (deeply pigmented). The ventral surface of the fish appears light (no pigmentation).

The ventral surface have more number of iridiocytes hence appear lighter in shade.

(Scomber scomber) (Canthigaster callistera)

Larvae change in pencil like form and become opaque (elvers).

Leptocephalus larvae of eel (Anguilla)Transparent larvae found in oceans.

VARIABLE COLOR RESEMBLANCE The ability of fish to change color , gradually in order to match its background more perfectly.

DISRUPTIVE COLORATION

The continuity of surface, bounded by a specific outline, that enables us chiefly to recognise an objects shape, disruption of this outline tends to conceal.

When the surface of the fish is covered by patches of contrasted color and tones, these patches tend to catch the eye of the predator and draws attention from the body shape.

The change in darkness of vertical dark bands on the body of angel fish (Pterophyllum scalare) and Batfish (Platax orbicularis) often confuse the predator during attack.

DISGUISE

When an animal exhibit a color pattern, form or posture, such that it resembles either an animal or a plant or sometimes a lifeless object.

Deflective marks are important here, thought of deflecting the animal to more or less vital parts of body to some other parts.

Amia (bowfin)

The eye spot as a deflective mark on the tail.

Chaetodon unimaculatus (Butterfly fish)

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Some forms of coloration of fish appear to advertise or to reveal rather to conceal their presence.

Warning coloration, threatning coloration, Cleaning and indication of mating are its important types.

Serpent eels (Ophichthyidae)

They have banded coloration similar to that of the venmous sea snake, for which it would be to their advantage to be mistaken.

Ameca splendensTerminal yellow band on caudal fin of male fish attracts females.

REFERENCESBOOKS:Physiology of fishes by J.M Odiorne.Ichthyology by Lagler, Bardach, Miller , PassinFish biology & Fisheries by S.S Khanna & H.R Singh.Internet sources: https://www.aqua-fish.net/fish/lifalili-cichlidhttps://fishprofiles.com/profiles/marine/Cichlids