Yellowtail (Seriola quinqueradiata) and "Ayu" (sweet fish, Plecoglossus altivelis) are most commonly cultured fishes in Japan. Body lipid contents of these cultured fishes are much higher than those of natural fishes because of over supplements of lipids in diets to promote growth. On the other hand, production of canned tea drinks has been increasing for the last few years. Greater parts of tea grounds which is by-products of tea drinks are discarded. In the present study, the effects of green tea extracts and grounds on growth and lipid content in two types of cultured fishes were examined. In yellowtail, the accumulation of body lipids was suppressed by the supplementation of 3.6% green tea grounds and 0.7% green tea extracts in the diets. In Ayu, it was suppressed by the supplementation of 1% green tea extracts in the diets, while the effect of tea grounds were not significant. The fishes cultured by the green tea extracts or tea grounds-supplemented diets were commonly decreased in average body weights, but their condition factors were kept at the same levels as the control.
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