Table I. — Production cost of federal fish and hatcheries in 1947. 1956. 



I96X. and 1970. 



Ratio of weight offish feed used to weight offish produced. 



Trout 1970: 



Average production per man-year 10 metric ton 



Average production, liters per second 46 kg 



Wanmvuter Fish (1970): 



Average production per hectare 170.(KK) fish 



Average production per man-year 725.(K)0 fish 



reduced sevenfold since the 19th centui^, when in- 

 flation is considered, and have decreased 25% since 

 the advent of pelleted diets. However, the cost of 

 rearing salmon has remained somewhat stable. Cur- 

 rent cost figures were not available for state and 

 commercial hatcheries; however, it is believed that 

 their production costs are somewhat similar to costs 

 listed for federal hatcheries. 



TYPES OF FISH CULTURE 



It has long been the custom in the United States to 

 classify fish hatcheries into two types — extensive, 

 where large water areas are used to supply both the 

 nutritional and environmental needs, and intensive, 

 where the fish are confined in small ponds or tanks, 

 their nutritional needs met by hand feeding, and their 

 environmental needs met by rapid exchanges of 

 water in the pond. By tradition, extensive culture 

 methods have been used to rear warmwater and 

 cool-water species (temperatures I5°-27°C), while 

 intensive culture has been practiced for the cold- 

 water species (I0°-16°C), in the family Salmonidae. 

 This distinction is beginning to disappear however, 

 as improved technology is demonstrating the prac- 

 ticability of rearing such v\armwater species as 



channel catfish, htcilunts piinctalits. and striped 

 bass, Moronc saxiiilis. by intensive culture 

 methods. 



Extensive Fish Culture 



The extensive fish culturist, or pondfish culturist 

 as he is more commonly called, is basically an 

 ecologist. His job is to maintain optimum oppor- 

 tunities for fish to spawn and grow under seminatural 

 conditions. He hopes to improve upon nature by 

 increasing the productivity of the pond. High survi- 

 val rates are achieved by eliminating competition by 

 other fish and by holding cannibalism to a minimum 

 through the prevention of a size spread of the fish in 

 the pond. In order to maintain uniform size, it is 

 essential that the fish spawn at the same time. This 

 is achieved with channel catfish and striped bass by 

 hormone injection. The spawning time of species 

 such as sunfishes. which are allowed to spawn in the 

 pond, is controlled by separating the sexes and hold- 

 ing them in cold water until seasonal water tempera- 

 tures have reached the desired level. 



Attempts are being made to gain greater control 

 over the spawning and survival of even these 

 species. Limited success in this direction has been 



68 



