Fish Hatchery Management - fisheries & aquaculture

172 FISH HATCHERY MANAGEMENTripens males as early as three days after injection, and advances slightly thespawning period for females, but may lower the fertility of the eggs. Injectionof mammalian gonadotropin into adult salmon fails to hasten thedevelopment of spawning characteristics, and there is no change in thetime of maturation.Acetone-dried fish pituitaries from common carp, buffalo, flathead catfish,and channel catfish have been tested and all will induce spawningwhen injected into channel catfish (Figrr.e 58). Carp pituitary material alsoinduces ovulation in walleye. The pituitary material is finely ground,suspended in clean water or saline solution, and injected intraperitoneallyat a rate of two milligrams of pituitary per pound of broodfish (Figure 59).One treatment is given each day until the fish spawns or shows resistanceto the hormone. Generally the treatment should be successful by the thirdor fourth day.Goldfish have been injected with human chorionic gonadotropin (HCG)in doses ranging from l0 to 1,600 International Units (IU) l"tonly thosefemales receiving 100 IU or more have ovulated. One hundred IU of HCGis comparable to 0.5 milligram of acetone-dried fish pituitary. In some instancesgoldfish will respond to two injections of HCG as low as 25 IU,when given 6 days apart. White crappies injected with 1,000, 1,500, andFrcunt 58. Collection of pituitary gland (arrow) from a common carp head. Thetop of the head has been removed to expose the brain. (Fish Farming ExperimentalStation, Stuttgart, Arkansas.)