210 FISFi HATCHERY MANAGEMENT 



pellets provide for more complete consumption of the feed. Feeding rates of 

 0.v5 to 10% of fish weight per day reduce the chance for feed wastage. Less 

 feed wastage results in far less pollution of the water during feeding and a 

 comparable reduction in cleaning of ponds and raceways. Pelleted feeds are 

 adaptable for use in automatic feeders. 



Many combinations of feedstuffs were tested as pelleted feeds; some 

 failed because the pellets were too hard or too soft; others did not provide 

 the nutrient requirements of the fish. 



Along with the testing and development of dry feeds, fish nutrition 

 researchers, relying largely on information concerning nutrition of other an- 

 imals such as chicken and mink, began utilizing and combining more and 

 more feedstuffs. 



Commercial fish feeds were pelleted and marketed in advance of open- 

 formula feeds. A few commercial feeds failed to produce good, economical 

 growth and to maintain the health of the fish but, by and large, most were 

 very satisfactory. 



Several items must be considered in developing an adequate feeding pro- 

 gram for fish. These include the nutrient requirements for different fish 

 sizes, species, environmental conditions, stress factors, types of feed, and 

 production objectives. General feeding methods are important and will be 

 discussed extensively in the last part of this section. 



It would be difficult to determine which factor has the greatest effect on 

 a hatchery feeding program. In all probability, no one factor is more im- 

 portant than another, and it is a combination of many that results in an ef- 

 ficient feeding program. Application of the available knowledge of fish nu- 

 trition and feeding will result in healthy, fast- growing fish and low produc- 

 tion costs. A fish culturist must be able to recognize the factors affecting 

 feed utilization and adapt a feeding program accordingly. 



Factors Influencing Nutritional Requirements 



The physiological functions of a fish (maintenance, growth, activity, repro- 

 duction, etc.) govern its metabolism and, in turn, determine its nutritional 

 requirements. Metabolism is the chemical processes in living cells by which 

 energy is provided for vital processes and activities. 



WATER TEMPERATURE 



Apart from the feed, water temperature is probably the single most impor- 

 tant factor affecting fish growth. Because fish are cold-blooded animals, 

 their body temperatures fluctuate with environmental water temperatures. 

 Negligible growth occurs in trout when the temperature decreases to 38°F. 

 The lower limit for catfish is about 50°F. As the temperature rises, growth 



