Influence of Dietary Protein and Lipid on Apparent Heat Increment of Rainbow Trout,Salmo gairdneri

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Abstract
Oxygen uptake attributable to apparent heat increment (AHI) in rainbow trout, Salmo gairdneri (10-15 g), induced to swim at .simeq. 2 BL .cntdot. s-1 was influenced by dietary energy intake and diet composition. Twelve balanced diets were tested, with protein levels of .simeq. 34, 40, 48 and 60% and lipid levels of .simeq. 7, 15, and 23% factorally combined. Diets supplying 34% protein and 23% lipid (protein to energy ratio of 94.3 mg .cntdot. kcal-1) resulted in the lowest AHI of all diets tested, indicating most efficient utilization of dietary protein. At a dietary lipid level of 23%, dietary protein levels lower than 34% may result in a further reduction in AHI. Duration of elevated metabolism following feeding was independent of dietary protein and lipid level, as well as dietary energy intake. AHI of rainbow trout represented the equivalent of 15-24% of the digestible energy intake, depending on diet composition. A reduction in dietary protein with a concomitant increase in dietary lipid in the formulation of feeds for aquaculture purposes could enhance growth efficiency by reducing the energy expenditure for AHI.