168 FISH HATCHERY MANAGEMENT 



The activation of sperm, however, does require exposure to either water 

 or female ovarian fluid. The sperm are active for a longer period when di- 

 luted with an isotonic salt solution or ovarian fluid than they are in water. 

 Sperm activated in ovarian fluid without the addition of water will fertilize 

 the egg readily and have the additional benefit of prolonged viability. This 

 is of particular importance when large volumes of eggs must be fertilized 

 with small quantities of sperm. 



Contaminants associated with the spawning operation also may have a 

 significant effect on egg fertility. Although skin mucus itself has not been 

 shown to reduce fertility, there is a good possibility that it can carry a con- 

 taminant such as the anesthetic used. Therefore, mucus should be kept out 

 of the spawning pan. Occasionally, blood will be ejected into the spawning 

 pan from an injured female; fish blood clots quickly and may plug the mi- 

 cropyle of the eggs, through which the sperm must enter. Occasionally, 

 broken eggs will result from the handling of females either prior to or dur- 

 ing spawning. Protein from broken eggs will coagulate and particles of 

 coagulated protein may plug the micropyle, thus reducing fertilization. If 

 large numbers of ruptured eggs occur, fertility sometimes may be increased 

 by placing the eggs in a 0.6% salt solution. This will cause the protein to 

 go back into solution. 



Fertilization can be estimated by microscopically examining a sample of 

 eggs during the first day or two after fertilization. The early cell divisions 

 form large cells (blastomeres) that readily can be distinguished from the 

 germinal disk of unfertilized eggs at 10 x magnification. To improve the 

 examination of embryos, a sample of eggs can be soaked in a 10% acetic 

 acid solution for several minutes. Unfertilized germinal disks and the em- 

 bryos of fertilized eggs will turn an opaque white and become visible 

 through the translucent chorion. A common procedure is to examine the 

 eggs when the four- cell stage is reached. The rate of embryonic develop- 

 ment will vary with temperature and the species of fish. This method may 

 not be suitable on eggs of some warmwater species. 



Gamete Storage 



Sperm of rainbow trout and northern pike have been stored and transport- 

 ed successfully. The sperm, with penicillin added, is placed in dry, sterile 

 bottles and then sealed. The temperature is maintained at approximately 

 32°F in a thermos containing finely crushed ice. Undiluted brook trout 

 sperm has been stored with some success for as long as 5 days. The sperm 

 should be taken under sterile conditions, kept free from all contaminants, 

 chilled immediately to 35°F, and refrigerated until needed. This procedure 

 also has been used to store rainbow trout sperm for a 7-day period. Some 

 workers, however, prefer to store brook trout milt for not more than 24 



