Fish Hatchery Management - fisheries & aquaculture

168 FISH HA'I'CHERY MANAGEMENTThe activation of sperm, however, does require exPosure to either wateror female ovarian fluid. The sperm are active for a longer period when dilutedwith an isotonic salt solution or ovarian fluid than they are in water.sperm activated in ovarian fluid without the addition of water will fertilizethe egg readily and have the additional benefit of prolonged viability. Thisis of particular importance when large volumes of eggs must be fertilizedwith small quantities of sperm.Contaminants associated with the spawning operation also may have asignificant effect on egg fertility. Although skin mucus itself has not beenshown to reduce fertility, there is a good possibility that it can carry a contaminantsuch as the anesthetic used. Therefore, mucus should be kept outof the spawning pan. Occasionally, blood will be ejected into the spawningpan from an injured female; fish blood clots quickly and may plug the micropyleof the eggs, through which the sperm must enter. Occasionally,broken eggs will result from the handling of females either prior to or duringspawning. Protein from broken eggs will coagulate and particles ofcoagulated protein may plug the micropyle, thus reducing fertilization. Iflarge numbers of ruptured eggs occur, fertility sometimes may be increasedby placing the eggs in a 0.6%r salt solution. This will cause the protein togo back into solution.Fertilization can be estimated by microscopically examining a sample ofeggs during the first day or two after fertilization. The early cell divisionsform large cells (blastome.es) that readily can be distinguished from thegerminal disk of unfertilized eggs at l0xmagnification. To improve theexamination of embryos, a sample of eggs can be soaked in a 10'/o aceticacid solution for several minutes. Unfertilized germinal disks and the embryosof fertilized eggs will turn an opaque white and become visiblethrough the translucent chorion. A common procedure is to examine theeggs when the four-cell stage is reached. The rate of embryonic developmentwill vary with temperature and the species of fish. This method maynot be suitable on eggs of some warmwater species.Gamete StorageSperm of rainbow trout and northern pike have been stored and transportedsuccessfully. The sperm, with penicillin added, is placed in dry, sterilebottles and then sealed. The temperature is maintained at approximately32'F in a thermos containing finely crushed ice. Undiluted brook troutsperm has been stored with some success for as long as 5 days. The spermshould be taken under sterile conditions, kept free from all contaminants,chilled immediately to 35'F, and refrigerated until needed. This procedurealso has been used to store rainbow trout sperm for a 7-day period' Someworkers, however, prefer to store brook trout milt for not more than 24