PIGMENT AND COLOUR CHANGE IN FISHES

Balwant SinghM.Sc. (AAS)

Pigment And Colour Change In Fish es

• Colourations in fishes is due to the presence of various kinds of pigments in the integument several species are brightly coloured exhibiting beautiful characteristic patter white other have a uniform shade .

• Some of the beautifully colour fish water fishes species are the Carassious (gold fish )Colisa ,Botia and Noemachelus.

• The bright colour are seen In the live or freshly killed fishes .

• Colour in fish is due to presence of Chromatophore and iridocytes.

• The chromatophore and orodocytes are present in the integument above and below the scales .

• Their number various in different species and in different part of deferent species and in deferent part of the body of the same species .

CHROMATOPHORES

• The chromatophore are branched cell lying in the dermis and they are called Erythrophores (red /orange) Xanthophore(yellow) or Melanophores (Black) and contain various type as pigment such as Carotenoid (Yellow ,Red) Melanin(Black),Purine (white or silvery) , Flavins (yellow) .

• Other colour like the blue ,green and brown are due to the mixing of three kinds of chromatophore in various proportion .

• The yellow red and orangs pigment are taken throught the food while the black pigment are the result of breckdown the amino acid (tyrosine)

• Usually chromatophore are large in number an the ventral side

• The relative number of chromatophores ,kind of pigment presint in them and the body result on a variety of colour pattern seen in the fish spieces

• In the sword tail,Xiphophoorus helleri, the beautiful colouration is due to the presenceof Xanthoerythrophores ,which contaninyellow pigment in the process of the cell .

• The red pigment granules consist of an outer limiting membrane and inner lamellae

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IRIDOCYTES

• The iridocytes is specialized cells which are also called “Mirror cell” due to the reffectinggreat power possessed by them .

• The iridocytes contain guanine which is white apaque or crystalline material and occur in the form of crystals ,granules, platelets .

• The iridocyte give white or silvery colour to the body .

CHANGE IN COLOUR IN FISHES

• Several species of fishes can change their colour so as adjust it to the surrounding.

• A temporary change in colour is effected by rearrangment of pigment granules , but a semi permanent change colour slowly by an increase or decrease in the total number of chromatophores.

• The when a fish moves to a darker environmentand has to stay there for some time , a slow change in colour taken place.

• Generally change in colour of the fish is due to

• Cecentration of the pigment towards the centresof the cells or their dispersion towards the peryphery.

• The time reqired to bring about the concerntration or dispersion of pigment , varies in different (in thire habitat other factors )Species

• Sometime individual of a species deffer widellyin their colour due o defferent in their habitat

• Other factor such as age, sex ,health ,and emotion also influence the colour of a fish .

MECHANISM OF COLOUR CHANGE

• Migration of pigments in the chromatophore to bring about change in colour is coordinated by two methodes .

• Through hormones and through nerves

• Some species make use of only one of these mechanism , while other depend on both .

• Its has been suggested the agrrregation and dispersion of related to gelation (solidification of liwuide )and solation (changing from a liqued to get of the protoplasm in the cell .

• Other have suggested that contraction and relation of the fibrils present between the outer and inner membranes are respensible for the movement of granules.

• Study on oryzia latipes , seem to indiate a change in electric pontential as the mechanism to couse movement of pigment granules .

NEURAL CONTROL

• The chromatophore in several species are

supplied with nerves ,and a neurenesproduced chemichal messenger called

neurohumors to active them .

• It is belived that ther are two kind of nerves fibrehaving apposite effects .

• Neurohumors secret by one kinds of fiber cause pigment dispersion ,while the other bring about their cencentration .

• It has been observed that cutting of nerves supplied to a particular area influencing the chromatophores of that area .

• In Phoxinus phoxinus, nerves stimulation bring about aggregation of melanin , and melanindispersing nerve fibers is also present in this species .

• Neural control a bring about a rapid change inthe colour .

• But controle through harmones is relative as slow process .

HORMONAL CONTROL

• In several species of fish , migration of pigmentgranules in chromatophore in under the control of pitutary gland .

• It has been observed the colour of the fishes becomes light aggrigation of the pigment after hypophysectomy (removel of pitutary gland ).

• Colouration of such a fish is restored temorarily .

• It pitutary extract is injected into the body .

• However some species do not respond to hypophygosectomy or pitutary injection, suggesting that their melanophore are not under the control of harmone or more than one kinds of hormones are needed to elicit response in them .

• It is well known that the melanophore stimulating hormone (M.S.H) or intermedian is secreted by the pors intermedia of the hypophysis .

• M.S.H bring about dispersion so the pigment in melanohormone causing the skin to become darker .

• Its absentce resultes in the lighter shade ,due to aggrigation of pigment .

• According to some authers a melanophoreconcentration haris secreted in the hypothalamusand a transported to pitutary for storage .

• It has also been suggusted that a melanophoresrelease harmone (M.S.H) and a melanophorereleaase inhabiting harmones (MRIH)may be produced by the hypothalamus.

• Thus hypothalamus exercise control over the secretion of MSH (inter media )from the pitutarygland beside the above , adrenaline also produced concetration sffect on pigment of melanophores.

• Thyroxine produced by the thyroid gland is also reportes influence the colour of the skin in some species .

• In the Eel Anguilla anguilla , colour change in under neural as well as harmonal control .

• When treted with adrenaline ,pigmentconcentration has been abserved in the eels.

• Thus hormonal control ovarrides neural control .

• But fundulus neuralcontrol of melanophore is stronger and dominantes over the hormonalcontrol .

• In shark and rays (condricthyes) , the response to black and white background is affected by the M.S.H ,and their appear to be little neural controlof melanophores .

• How ever pin eal play important role in colourchange in shark and rays.

• Fishes have been divided into three groups depending upon the degree of neural control over its melanophores.