No abstract

The supplemental effect of amino acids (AAs) to a soy protein concentrate (SPC) diet for red sea bream Pagrus major was evaluated for different‐sized fish. The fish were fed artificial diets based on 52% SPC for 60 days in juvenile (mean weight 11.7 g) and for 153 days in yearling (mean weight 178 g). To these diets L‐lysine hydrochloric acid (LS), DL‐methionine (MS) and both L‐lysine and DL‐methionine (LMS) were supplemented. A control diet without AA supplementation (NOS) and a reference diet based on brown fish meal (BFM) were also tested. In the juvenile fish, the growth performance of the MS group was significantly higher than the NOS group. The growth performance was further improved by the dietary supplementation of both Lys and Met (LMS group). Lenticular opacity was not observed in these two dietary groups. On the other hand, the growth performance of the NOS and LS groups was lowest, and the incidence of lenticular opacity of the LS group was higher rather than the NOS group. In the yearling fish, feed conversion of the LMS group was slightly higher than the NOS group, but the growth performance of the LMS group was similar to the NOS group. These parameters were similar or slightly lower in the LS or MS groups compared with the NOS group. Lenticular opacity was not observed in any dietary groups for yearling fish. In both juvenile and yearling fish, the performances of the BFM groups were superior to the other dietary groups. The results for juvenile fish indicate that the quality of the SPC diet is improved by the Met supplementation, and further improved by both Lys and Met supplementation. Furthermore, the results in the present study suggest that the AA requirement of red sea bream changes with growth and/or age.

To elucidate the hemolytic suppression roles of taurine and the necessity of dietary taurine supplementation in yellowtail Seriola quinqueradiata fed a diet without fishmeal, juvenile fish with an initial body weight of 250 g were fed for 40 weeks in floating net cages on soybean protein diets supplemented with 0, 3.0, 4.5 and 6.0% taurine. Taurine concentration of the experimental diets were 0.03, 33.9, 52.8 and 71.6 mg/g, respectively. On the 21st week, fish fed the taurine unsupplemented diet had inferior growth and feed performances, higher death, and there were incidences of green liver and hemolytic anemia. In this group, hepatic and plasma taurine concentrations, serum osmolality and osmotic tolerance of erythrocytes (EC50 value) were significantly lower, and plasma hydroperoxide concentration was markedly higher than in the taurine supplemented groups. These conditions markedly improved corresponding with the increase of dietary taurine concentration. These results indicate that taurine plays a role in hemolytic suppression through osmoregulation and biomembrane stabilization in fish. In addition, it is suggested that yellowtail requires dietary taurine as an essential nutrition for maintaining physiological condition normally.

This study was performed to evaluate the efficacy of taurine supplementation for preventing green liver syndrome and improving growth performance in red sea bream Pagrus major fed a low-fishmeal (FM) diet. Yearling red sea bream were fed for 34 weeks on low-FM diets either supplemented with taurine, or without taurine, and the tissue taurine and bile pigment concentrations were measured. Compared to the fish fed the FM diet, fish fed the low-FM diet without taurine supplementation resulted in inferior feed performances and higher incidence of green liver related to the morphological transformation of the erythrocytes. In these fish, the hepatopancreatic taurine concentration was significantly lower and hepatopancreatic biliverdin concentration was high compared to the fish fed the FM diet. These parameters were markedly improved by taurine supplementation of the low-FM diet and were similar in levels to the fish fed the FM diet. These results indicate that green liver appearance and inferior feed performances of red sea bream fed the low-FM diet without taurine supplementation were caused by dietary taurine deficiency, and indicate the requirement of taurine supplementation to low-FM diets for red sea bream.KEY WORDS: alternative protein, bile pigment, green liver syndrome, low-fishmeal diet, red sea bream, taurine.