In order to elucidate the participation of L-cysteinesulphinate decarboxylase (CSD) in taurine synthesis in Japanese¯ounder, and the synthetic ability of taurine in other ®sh species, hepatic (or hepatopancreatic) CSD activities of several ®sh species were compared. Enzyme activity was determined by measuring the production of hypotaurine during an incubation of crude enzyme preparation with L-cysteinesulphinate as a substrate. HPLC was used for the analysis of hypotaurine. The enzyme activities of ®sh were lower than those of mammals. Japanese¯ounder Paralichthys olivaceus (Temminck et Schlegel) showed half the activity of rainbow trout (Oncorhynchus mykiss Walbaum). As activity was almost constant throughout the ®sh growth cycle, CSD does not seem to be responsible for low production of taurine in juvenile Japanese¯ounder. On the other hand, CSD activity was not present in yellowtail (Seriola quinqueradiata Temminck et Schlegel), blue®n tuna Thunnus thynus (Linnaeus) or skipjack (Katsuwonus pelamis (Linnaeus)). The inability to synthesize taurine and the possible dietary requirement for taurine is suggested in these ®sh species.
caudal fin, and abnormal formation of pterigiophores was observed in the fish fed this level of VA. These results suggest that VA seems to be effective in preventing the abnormal coloration caused by Tien-tsin Artemia, but the excess amount of this vitamin can exert ill effects on normal growth of flounder.
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