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FISH HATCHERY MANAGEMENT 



ripens males as early as three days after injection, and advances slightly the 

 spawning period for females, but may lower the fertility of the eggs. Injec- 

 tion of mammalian gonadotropin into adult salmon fails to hasten the 

 development of spawning characteristics, and there is no change in the 

 time of maturation. 



Acetone-dried fish pituitaries from common carp, buffalo, flathead cat- 

 fish, and channel catfish have been tested and all will induce spawning 

 when injected into channel catfish (Figure 58). Carp pituitary material also 

 induces ovulation in walleye. The pituitary material is finely ground, 

 suspended in clean water or saline solution, and injected intraperitoneally 

 at 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 resistance 

 to the hormone. Generally the treatment should be successful by the third 

 or fourth day. 



Goldfish have been injected with human chorionic gonadotropin (HCG) 

 in doses ranging from 10 to 1,600 International Units (lU) but only those 

 females receiving 100 lU or more have ovulated. One hundred lU of HCG 

 is comparable to 0.5 milligram of acetone-dried fish pituitary. In some in- 

 stances goldfish will respond to two injections of HCG as low as 25 lU, 

 when given 6 days apart. White crappies injected with 1,000, 1,500, and 



Figure 58. Collection of pituitary gland (arrow) from a common carp head. The 

 top of the head has been removed to expose the brain. (Fish Farming Experi- 

 mental Station, Stuttgart, Arkansas.) 



