Fish Hatchery Management - fisheries & aquaculture

BROODSTOCK. SPAWNING. AND EGG HANDLINGt57*L*-t'4B **--X*I..4FIGURE 49. Equipment used for spawning wild coolwater fishes (trap net shownin backgrouna). fne males and females are held separately in holding tanks containingan anesthetic (e, S). e bench with a spawning pan (C) is provided forthe spawn taker. (FWS photo.)The fish is then held with the belly downward over a pan, and the eggs areforced out gently by a massaging movement beginning forward of the ventand working back toward it. Care should be taken to avoid putting pressuretoo far forward on the body as there is danger of damaging the heartor other organs (Figure 50). After the eggs have been extruded, a smallamount of milt (spe.-) is added from a male fish. Milt is expressed from aripe male in much the same manner as the eggs are taken from a female(Figure 51). If either eggs or milt do not flow freely, the fish is not sufficientlyripe and should not be used. The fish should be examined frequently,as often as twice a week, to determine ripeness. Fish rarely spawn oftheir own accord under hatchery conditions, and, if they are not examinedfor ripeness frequently, overripe eggs will result. Muskellunge, however,will often spawn on their own accord.The two generally accepted procedures for handling eggs during fertilizationare often referred to as the wet and dry methods. In the dry methodof fertilization,water is not introduced before the eggs are exPressed intothe pan, and all equipment is kept as dry as possible. Sperm and eggs arethoroughlymixed and usually left undisturbed for 5 to 15 minutes before