Fish Hatchery Management - fisheries & aquaculture

142 FISH HATCHERY MANAGEMENTfeet out from shore. As soon as fry become numerous, they can be capturedwith a small fry seine and transferred to rearing ponds at the rate of300,000 to 600,000 fry per acre. From this stocking rate, a harvest of about150,000 fathead minnows can be expected.During the first few weeks of life following transfer to the rearing pond,fry grow very rapidly. Within 4 to 8 weeks, many of these fish will matureand begin to spawn. When this occurs, the pond may become overstockedand the fish become stunted. The excess fry should be transferred toanother pond or destroyed.A productive pond should have a good plankton density; a Secchi diskreading of about l2 inches should be maintained. Fathead minnows readilyaccept a formulated diet, usually in the form of meal. The amount recommendedis 2'li of body weight per day, not to exceed 25 pounds per dayper acre. In 6 to 10 weeks this procedure will produce 2-inch forage organisms.GOLDF'ISHGoldfish are good forage fish. This is a hardy species that prospers duringhot weather. Goldfish feed largely on plankton, but will take insects andvery small fish. They reproduce in large numbers and grow rapidly.Goldfish normally start spawning when the water reaches 60"F and continueto spawn throughout the summer if the temperature remains above60'F and the fish are not overcrowded. The favorite spawning time is rightafter sunrise on sunny days. The females lay their eggs on grass, roots,leaves, or similar objects. A female goldfish may lay 2,000 to 4,000 eggs atone time and may spawn several times during the season. The eggs areadhesive and stick to any object they touch. The live eggs are clear andturn brown as they develop; dead eggs are cloudy and opaque. The eggshatch in 6 to 7 days at a water temperature of 60'F.Goldfish averaging 0.25 to 0.75 pound reproduce well and should beused for broodstock. Broodstock overwintered in crowded ponds will notspawn in the ponds. Maximum egg production is obtained by keeping thebroodfish in the overwintering pond until after the last spring frost. Thenthe fish are stocked in the production ponds at the rate of 100-200 adultsper acre without danger of frost damaging the eggs or fry. Goldfish will acceptformulated feeds and feeding rates should be set to produce 2-3-inchfish in the shortest time.Broodstock ponds should be fertilized to insure that phytoplankton productionis sustained all summer. Secchi disk readings should be l8 inchesor less.Ponds should contain suitable natural vegetation or artificial spawningmaterial. The water level is commonly dropped in early spring to encouragethe growth of grass along the shoreline. When the ponds are filled,