EXPERIMENTAL BIOLOGY 



599 



allowed a volume of water of 1 dm 3 . Carnivorous fishes, crustaceans 

 and aquatic insects must be of about the same size and only a few in 

 each aquarium. To avoid cannibalism the parents must be separated 

 from the eggs, or spawn and the young, except when the parents brood 

 their offspring. Comparatively small vessels are sufficient for indolent 

 forms like tadpoles, salamanders, aquatic insects and most crustaceans. 

 In most cases when breeding, the larger the tank the more certain the 

 result and the more numerous the progeny. Some animals need stag- 

 nant slowly flowing water, others a rapid current, some always live in 

 the water, others only during certain times of the year and still others 

 only during certain stages in the life history. Sharp-angled stones are 



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Fig. 17. Museum of the Vienna Institution foe Experimental Biology. 



necessary for certain fishes and amphibia to scrape against in order to 

 remove from their skins such deadly enemies as the fungus Saprolegnia. 

 The annual natural range of temperature must be followed, especially 

 in the breeding of animals. Inhabitants of stagnant pools require a 

 range from 4°-35° C, those of slowly flowing, shallow waters 4°— 

 25° C, of the greater depths 4°-18° C, of rushing, rough mountain 

 brooks with shallow places 4°-15° C. and of caves 12°-17° C. Car- 

 nivorous animals need be fed only every other day, and because of the 

 restricted movement in confinement overfeeding leads to fatty de- 

 generation, especially of the reproductive organs. If diseases appear 

 the sick animals must be isolated and the aquaria very carefully 

 cleansed with hot water and the use of disinfectants. Saprolegnia and 



