170 FISHES CHAP. 



The interior of a Minnow-can is sometimes painted white, so 

 that the bait may assume a lighter colour, and thus become more 

 conspicuous in the deeper and darker water where Perch and 

 Pike abound. Hence the colour of a Fish may vary with its 

 surroundings ; and, as will shortly be shown, the capacity for 

 producing such changes under natural conditions is of the 

 greatest importance to Fishes in various ways. 



Change of coloration may take place through the develop- 

 ment of new chromatophores under the influence of new condi- 

 tions, and is then comparatively slow. Artificial illumination of 

 the unpigmented white side of a Flounder (Pleuronectes flesus), 

 by means of a mirror, induces the formation of chromatophores, 

 and produces a coloration more or less closely resembling the 

 upper pigmented side. 1 A similar change sometimes occurs as a 

 natural variation, and is then usually associated with structural 

 deformity in other respects. 



Coloration also varies with age, sex, ill-health, and even with the 

 emotions. Young or immature Fishes are often marked by bands, 

 bars, or blotches of colour (e.g. the Parr-marks of young Sal- 

 monidae), which, as they disappear when the Fish approaches the 

 adult state, are perhaps residual traces of ancestral coloration ; 

 although, no doubt, change of habits and surroundings are some- 

 times responsible for such colour changes as are observable during 

 growth. Conspicuous coloration is one of the most frequent of 

 secondary sexual characters, the colours of the male being brighter 

 than those of the female, particularly during the breeding season. 

 A diminution of colour has been noticed in the artificially-induced 

 pigmentation of the lower side of a Flounder when the Fish was 

 suffering from partial suffocation owing to the temporary failure 

 in the supply of fresh water, the normal colour returning when 

 the deficiency had been remedied. A similar pallor was caused 

 by fright when the same Fish was disturbed. 2 A nocturnal colour- 

 change has been recorded in the Tasmanian Trumpeter (Latris 

 hecateia). 3 In addition to the olive-green longitudinal bands 

 which are always apparent, there are visible at night five broad, 

 transversely-arranged, blackish bands. As illustrating the im- 

 portance of vision in colour-changes, it may be mentioned that in 

 a specimen of this Fish, living in a tank, which had been blinded, 



1 Cunningham and MacMunn, op. cit. p. 791, et seq. 

 2 Ibid. p. 800. 3 Saville Kent, Nat. Austr. p. 163. 



