COLOUR CHANGES 



523 



Though usually regarded as static, the guanophores of some fishes may 

 show movements similar to other chromatophores. Guanine crystals in the 

 iridocytes or guanophores of Gobius minutus, Callionymus lyra and Fundu- 

 lus heteroclitus are able to concentrate and disperse within the cells. The 

 guanophores also appear to expand on white backgrounds, and contract 

 on black ones, responses the reverse of those occurring in melanophores. 

 However, the behaviour of guanophores is poorly understood (54). 



The rapidity with which colour changes are accomplished in different 

 species shows much variation and is some index of the effectiveness of 

 nervous control over this response. In the American summer and winter 

 flounders Paralichthys dentatus and Pseudopleuronectes americanus, the 

 animals change from pale to dark in 1-5 days, and make the reverse change 







10 



40 



20 30 



lime (seconds) 



Fig. 12.11. Photoelectric Records of Colour Changes in Fundulus heteroclitus 

 on Suddenly Changing the Colour of the Background 



Hollow circles, light background, fish turning yellow. Solid circles, dark background, 

 fish turning brown. (Redrawn from Hill, Parkinson and Solandt (30).) 



in 2-7 days. It is noteworthy, however, that these times are shortened by 

 repetition, and in a specimen of the gulf fluke Paralichthys albiguttus, which 

 was repeatedly transferred from black to white, and vice versa, the time in 

 which a background response occurred was reduced from 5 days to less 

 than 2 min. In the cunner Tautogolabrus adspersus blanching and darkening 

 are carried out in 50 min, and in the common killifish Fundulus heteroclitus 

 in 40-60 sec (Fig. 12.11). Some times recorded for expansion and contrac- 

 tion of erythrophores are still more rapid, being accomplished in 15 sec in 

 the sea robin Prionotus strigatus and 22 sec in the squirrel fish Holocentrus 

 ascensionis (14, 30, 50). 



The chromatophores of teleosts have long been known to be under some 

 degree of nervous control. In a pioneer study on the turbot Scophthalmus 

 maximus Pouchet showed that by interrupting the sympathetic chain or 

 specific nerves the peripheral field distal to the injury darkened through 

 melanophore expansion, thus indicating that nervous impulses normally 

 cause the chromatophores to contract (Fig. 12.12). Subsequently, Ballo- 

 witz demonstrated the rich innervation of these structures. 



