302 n. S. BUREAU OP FISHERIES 



HIBERNATION 



Many of our native fresh-water fishes cease to feed when the water 

 becomes cold, some of them lying torpid for months, A moderate 

 warming of the fresh water before it is supplied to the fish tanks 

 induces the occupants to feed occasionall3% with the result that they 

 are less weakened by long semihibernation. Losses among captive 

 fishes are greater in spring than at other seasons of the year. Wild 

 fishes captured eaiiy in the spring are subject to the same fungus 

 troubles that afflict captive fishes after hibernation, and the losses 

 among them are greater. 



We do not subscribe to the theory that hibernation is beneficial to 

 northern animals merely because it is natural. In reality it is an 

 unavoidable test of endurance b}' which undoubtedly the}' are weak- 

 ened more or less. Nature eliminates those individuals whose vitality 

 is not equal to the rigid conditions that she imposes. The survival 

 of the hardier under natural conditions would be less certain if the 

 hibernating period were to be prolonged imnaturally. The flying 

 squirrels that sought winter protection in my deserted mountain cabin 

 failed to survive in the uncovered lieaps of clothing wliere they hid. 

 They would have been warmer in the deep hollows of trees. We have 

 found ground squirrels frozen under similar conditions. Virtually 

 nothing is known about winter losses among pond turtles, frogs, and 

 salamanders that fail to dig deep enough for safety. Captive box 

 tortoises that winter safely in cellars doubtless survive because such 

 situations are at least as warm as those they are able to find out of 

 doors. An early springtime must be of saving power to some of the 

 hibernating animals. There can be little doubt that most of the 

 fresh-water fishes and the larger salamanders would winter in better 

 condition in the aquarium if the water temperatures were maintained 

 at about 60°. Water of normal winter temj)erature is satisfactory 

 for Salmonidse and other fishes that continue to feed when water 

 temperatures are lowest. 



LONGEVITY OF FISHES IN CAPTIVITY 



A fair proportion of the species of fishes exhilsited in public 

 aquariums survives under the rCvStrictions of captivit}^ for many 

 years. A larger proportion, being less hardy, is more difficult to 

 provide for; while some kinds, needing foods not readily procurable 

 or altogether unobtainable in winter, do not live longer than a few 

 months. Tropical fishes kept in northern aquariums can not be sup- 

 plied with the variety of foods obtainable among their native reefs. 

 The restricted amount of live food available probably has as much 

 to do with losses as any factor in aquarium management. 



In the New York Aquarium, which is well supplied in summer 

 with small marine invertebrates, losses are reduced to the minimum 

 during more than half the year. With most aquariums the food 

 supply, especially in winter, is dependent upon what can be found 

 in the markets; nevertheless, many of them have records for certain 

 kinds of fishes that indicate a high average of success in keeping 

 them. 



