Abstract
Fingerling and juvenile grass carp ( Ctenopharyngodon idella) were fed elodea ( Elodea densa), coontail ( Ceratophyllum demersum), eurasian water milfoil ( Myriophyllum sp.) or a commercial catfish feed at 26°C or 20°C, respectively. Diet significantly affected consumption, digestion, growth and muscular fatty acid composition of grass carp. Fingerling grass carp fed Elodea at 26°C consumed a ration (wet weight) higher than their body weight, with a digestion efficiency around 50%, and achieved excellent growth. Fish fed other diets in this study grew more slowly and the growth rates were positively related to the daily intake of protein. Grass carp readily elongated and desaturated dietary linolenic acid into long chain polyunsaturated fatty acids. Dorsal muscle lipids from fish fed Elodea at 26°C contained 35% n−3 fatty acids and the n−3 fatty acid content in Elodea-fed fish was 7- or 4-fold more than in those fed catfish feed at 26°C or 20°C, respectively. Among the plant-fed fish, muscle docosahexaenoic (22:6 n−3) levels were very similar at 26°C while linolenic and eicosapentaenoic (20:5 n−3) acid levels varied. Grass carp selectively deposited dietary n−6 fatty acids in their muscle. Total n−6 fatty acid levels in all groups of fish were very similar at 26°C or 20°C regardless of the great differences in linoleic level among the experimental diets. The ratio of saturates to unsaturates in grass carp muscle fell in a narrow range (0.31–0.36) irrespective of large differences in this ratio among the diets (0.27–0.66).
Published Version
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