190 



FISH HATCHERY MANAGEMENT 



Table 20. number of days and daily lEMi'ERAruRE units required for 



TROUT EGGS TO HATCH". (SOURCE: LEITRITZ AND LEWIS l<)7(i.) 



WATER TEMPERATURE, T 



SPECIES 



35 



40 



45 



50 



55 



60 



Rainbow trout 



Number of days to hatch 

 Daily temperature units 



Brown trout 



Number of days to hatch 

 Daily temperature units 



Brook trout 



Number of days to hatch 

 Daily temperature units 



Lake trout 



Number of days to hatch 

 Daily temperature units 



Spaces without figures indicate incomplete data rather than a proven inability of eggs to 

 hatch at those temperatures. 



group of eggs at a specific temperature. The required temperature units to 

 hatch several species of fish are presented in Tables 20 through 23. 



Factors Affecting Egg Development 



Three major factors that affect the development of the embryos are light, 

 temperature, and oxygen. 



LIGHT 



Direct light may have an adverse effect on developing fish eggs. The most 

 detrimental rays are those in the visible violet-blue range produced by cool 

 white fluorescent tubes. Pink fluorescent tubes, which emit light in the yel- 

 low to red range, are best suited for hatchery use. The best practice is to 

 keep eggs covered and away from direct light. 



In general, embryos of fishes subjected to bright artificial light before 

 the formation of eye pigments will suffer high mortality at all stages of 

 growth. Affected eggs exhibit retarded development and accelerated hatch 

 and, if they do hatch, the fingerlings often have reduced growth and severe 

 liver damage. Eggs exposed to artificial light after formation of eye pig- 

 ments are less susceptible to light rays but still exhibit increased mortality 

 and reduced growth, or both. 



