l8 MAINTAINING FISHES 



that for work not involving attempts to produce natu- 

 ral spawning, the length of day should correspond to 

 the seasonal temperatiure at which the fishes are being 

 held. When one is attempting to produce a natural 

 spawning it may be necessary to systematically in- 

 crease illumination for spring-spawners or systemati- 

 cally decrease it for fall-spawners. In connection with 

 the control of spawning one should consider the possi- 

 bility of using pituitary hormones. (See section on 

 control of reproduction.) 



Water Supply 



TEMPERATURE: The breeding and holding of 

 fishes requires fairly accurate control of water tempera- 

 ture, and experimental conditions usually prescribe a 

 particular water temperature. Temperature charac- 

 teristics of water are dependent upon the source. Well 

 water is in the 50° to 60° F. range and remains ap- 

 proximately the same summer and winter. Lake, 

 stream, and tap water are markedly affected by air 

 temperature, although water from a spring fed stream 

 and water from 20 or more feet of depth from a lake 

 have a stable temperature quite similar to well water. 

 In any case facihties should be available for heating 

 water prior to its use. For most installations a con- 

 ventional gas or oil type water heater of high capacity 

 is the best choice. In many cases it is desirable to have 

 duplicate water supply lines, one for cold water and 

 the other for heated. 



CARBONATE CONTENT: The minimal mineral 

 content of water does not usually constitute a problem 

 with the possible exception of the carbonate content. 



