280 



ZOOLOGICAL SOCIETY BULLETIN 



So far the fish culturists have not found it difficult 

 to propagate artificially. It has been introduced 

 into Lake George and other New York waters. 

 This fish should not be confused with the recently 

 described golden trout of the high Sierras of 

 California. 



HOW FISHES CHANGE COLOR. 



OF the sixty or more different kinds of tropical 

 fishes which may be seen in the Aquarium 

 from time to time, there are a large number which 

 have power to change their colors very quickly. 

 Among these maybe mentioned the different hinds, 

 groupers {Epinephclus) and the coney (Bodianiis 

 julvus). 



The changes are often very marked. A grouper 

 of a pale coloration, showing very few markings and 

 swimming near the surface of the tank, may settle 

 to the bottom and in a moment reveal all its 

 characteristic dark bands very sharply. A coney, 

 appearing chiefly red, may in a few moments put 

 off the red color entirely, turning uniformly pale; 

 a little later the lower half of the body may become 

 almost white, the upper half at the same time being 

 very dark. 



A tropical fish swimming actively about its tank 

 has usually a different coloration than that assumed 

 when at rest. Settling down upon the white gravel 

 or hiding among the dark rockwork, it is quite 

 likely to adapt its color accordingly. Fishes reflect 

 their surroundings very readily. While the colors 

 of some fishes are developed chiefly during the 

 season of courtship, with most species they are 

 connected with the need of protection and in many 

 cases may be developed almost instantly. 



The frightening of tropical fishes which change 

 color readily, almost always results in a change of 

 some character. When fishes change color the 

 change corresponds of course with the color- 

 changing ability of each particular species. 



The color cells of fishes, known as chromatophores, 

 lie in the deeper layer of skin ; and the tints, whatever 

 they may be, are brought about by the contraction 

 and expansion of the cells as they assume a flat, 

 globular, or other form. 



It is the spasmodic action of the cells which gives 

 to the dolphin its celebrated color-changes during 

 its death convulsions. The cells may contain blue, 

 j'ellow, red, or other pigment, some colors being 



produced by the combined action of different col- 

 ored cells. 



The iridescence of fishes is produced in another 

 way. It is due to the presence of rejecting tissue 

 and depends upon the way in which the light is 

 reflected from it. 



FOUR YE.\RS OF CHANGE IN THE 

 AXOLOTL. 



THE axolotl, as at present understood, is the 

 larval or gilled form of a salamander, eight 

 or nine inches in length, known as Amblystoma 

 tigrinnm. 



It inhabits certain waters of the LTnited States, 

 extending southward as far as Central Mexico. 



.'\lthough long supposed to be a species with 

 permanent gills, it was discovered, from specimens 

 kept in captivity, that the gills were gradually 

 absorbed and the animal became the land-living 

 Amblystoma. 



It was also discovered that the animal sometimes 

 bred in its larval stage, without waiting for the final 

 stage supposed to be necessary for sexual maturity. 



A specimen which has long been undergoing 

 transformation in its tank at the Aquarium was 

 recently photographed in order that its appearance 

 might be compared with its appearance as recorded 

 by a photograph taken four years ago. The two 

 pictures shown on page 281 indicate more or less 

 clearly the changes which took place. 



When the first picture was made there were 

 four a.xolotls in the tank, all about the same size and 

 with gills alike. 



The second picture shows one of the animals with 

 its branching gills reduced by slow absorption to 

 mere useless stubs. As a breathing apparatus the 

 gills gradually failed until the axolotl had to go to 

 the surface of the water when in need of air. All 

 these specimens were of the white or flesh-colored 

 variety. 



A letter has just been received from Dr. S. E. 

 Meek, of the Chicago Museum, in reference to the 

 metamorphosis of the specimens in the Aquarium. 

 He expresses the opinion that in the literature 

 of the subject generally two species have been 

 confused and that the original "axolotl," Ambly- 

 stoma mexicamim, inhabiting lakes near the city of 

 Mexico, is an entirely distinct species, as was be- 

 lieved by Professor Cope. 



