Growth and energy budget in young grass carp,Ctenopharyngodon idellaVal., fed plant and animal diets

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Abstract
Young grass carp held under laboratory conditions were fed either duckweed or tubificid worms. Food consumption (C), faecal production (F), excretion (U), metabolism (R) and growth (G) were estimated for fish fed both diets. Fish fed tubificid worms had higher growth rates than those fed duckweed, in terms of wet weight, dry matter, protein, lipid and energy. Fish fed duckweed consumed more wet and dry matter than did the fish fed tubificids, but rates of protein and lipid consumption were lower. The energy budget was estimated to be 100C = 9F+ 8U+ 61R+ 22Gfor fish fed tubificids, and 100C = 35F+ 5U+ 51R+ 9Gfor fish fed duckweed. Linear relationships existed between specific growth rate in wet weight and rate of food absorption (consumption minus faecal production) in dry matter, protein or energy. Food type did not have a significant effect on these relationships. It was concluded that differences in growth rate between grass carp fed different diets were mainly caused by differences in absorption rate.