160 FISH HATCHERY MANAGEMENT 



The egg sample is placed on a clean glass slide with a small amount of 

 water. Magnification of 20 x provides a sufficiently wide field for examina- 

 tion of several eggs with enough magnification for detailed viewing of indi- 

 vidual eggs. 



Egg samples should be taken between 20 and 28 hours after hormone in- 

 jection. Approximately 16 hours are required for the effects of the hormone 

 to be detected in egg development. Early in the spawning season, it is 

 advisable to wait 28 hours before sampling because it usually requires 

 about 40 hours for ovulation, and eggs taken more than 15 hours before 

 ovulation cannot be accurately staged. Near the peak of the natural spawn- 

 ing season, ovulation may occur within 20 hours following injection and it 

 is prudent to sample earlier. 



It is impractical to predict ovulation in striped bass that are more than 

 15 hours from spawning as the eggs are very opaque and no difference can 

 be detected between 30- hour and 17- hour eggs. If opaque eggs are found, 

 the ovary should be resampled 12 hours later. 



At about 15 hours before ovulation, the ova assume a grainy appearance 

 and minute oil globules appear as light areas in individual ova. This is the 

 first visible indication of ripening. 



At 14 hours, the globules in some of the ova have become somewhat en- 

 larged while very small globules are evident in others. No distinct progress 

 can be detected in a few eggs. This mixed development may be confusing, 

 but in order to avoid over-ripeness, a prediction of spawning time should 

 be based primarily on the most advanced eggs. Uneven maturation persists 

 to some degree until approximately the 10- hour stage, after which develop- 

 ment progresses more uniformly. 



At 13 hours, the majority of ova will have enlarged globules and cleared 

 areas occupy over one- half of the surface of most eggs. 



At 12 hours, the first evidence of polarization of what eventually will be- 

 come the oil globule is apparent. The small globules begin fusion to form a 

 single globule. 



At 10 hours, polarization of the oil globule is complete. The entire egg is 

 more translucent than in earlier stages. 



At 9 hours, eggs begin to show more transparency in the yolk, although 

 the majority of the yolk remains translucent. 



It is difficult to describe differences between eggs that are 6, 7, or 8 

 hours from spawning. There is a continued clearing of the nucleus, and 

 with experience, the worker will be able to pinpoint the exact stage. How- 

 ever, to avoid over- ripeness, it is best to classify eggs in any of these stages 

 as the 6-hour stage and attempt to hand-strip the eggs. 



From 5 hours until ovulation, the ova continue to clear; at 1 hour, no 

 opaque areas can be detected. For more detailed information describing 

 this process consult the publication by Bayless 1972 (Figures 52-55). 



