192 fish hatchery management 



Table 23. time-temperature relationship and daily temperature units 

 req^uired for hatching muskellunge eggs, 



DAILY TEMPERATURE UNITS 

 TEMPERAI'URE °F DAYS TO HATCH TO HATCH (F) 



45 21 273 



47 20 300 



49 19 323 



51 18 342 



53 16 336 



55 14 322 



57 12 300 



59 10 270 



61 9 261 



63 8 248 



65 7 231 



67 6 210 



Eggs and fry of walleye tolerate rapid temperature fluctuations. Approx- 

 imately 390 daily temperature units are required for eggs to hatch in fluc- 

 tuating water temperatures, while only 230 daily temperature units general- 

 ly are required at more constant temperatures (see Table 22). 



Low water temperatures during spawning and incubation of largemouth 

 bass eggs can cause high egg losses. Chilling of the eggs does not appear to 

 be the direct cause of egg loss. Rather, it causes the male fish, which nor- 

 mally guards and fans the eggs, to desert the nest. As a result, the eggs are 

 left without aeration and die from suffocation. This is a common cause of 

 egg losses in areas that are marginal for largemouth bass production. 



Data gathered at the Weldon Striped Bass Hatchery, Weldon, North 

 Carolina, indicate that the optimum spawning temperature range for 

 striped bass is between 62 and 67°F. The minimum recorded temperature 

 at which spawning will occur is 55°F and the maximum temperature is 



yiT. 



OXYGEN 



Sac fry from eggs incubated at low oxygen concentrations are smaller and 

 weaker than those from eggs incubated at higher concentrations. The best 

 conditions for the optimal development of embryos and fry are at or near 

 100% oxygen saturation. As the development of an egg progresses, oxygen 

 availability becomes increasingly important. Circulation of water is vital for 

 transporting oxygen to the surface of the chorion and for removing meta- 

 bolites from the vicinity of the developing egg. Eggs provided with insuffi- 

 cient oxygen will develop abnormalities and their hatching may be either 

 delayed or premature, depending on the species. 



