Dietary taurine requirement and taurine-sparing effect of sulfur amino acid in juvenile rock bream, Oplegnathus fasciatus

Abstract

본 연구는 치어기 돌돔의 성장과 지질대사에 있어 타우린 투여 효능을 알아보고(실험1) 메티오닌과 시스테인으로 타우린의 절약효과를 평가하기위해(실험 2) 두 가지 실험이 동시에 수행되었다. 두 실험에서 하나의 어분이 기반이 된 사료가 대조구로 사용되었다. 실험1에서 사료에 타우린을 각각0.25, 0.5, 1.0, 1.5 와 3.0%를 첨가한 5개의 실험사료가 준비되었다(Tau0.25, Tau0.5, Tau1.0, Tau1.5 와 Tau3.0). 실험 2에서는 사료에 메치오닌과 시스테인을 0.5%수준으로 고정하고, 타우린을 각각 0, 0.25, 0.5와 1.0%를 첨가한 4개의 실험사료가 준비되었다(S+Tau0, S+Tau0.25, S+Tau0.5 와 S+Tau1.0). 평균무게가 2.72 ± 0.04 g (mean ± SD)인 치어기 돌돔을 25마리씩 3반복으로 10개의 실험구당 하나씩 사료가 공급되었다. 두 실험은 반순환여과방식으로 30개의 수조(40L)에서 수행되었다. 두 실험에서 하루에 어체중의 3~4%수준으로 배합사료가 공급되었다. 각 수조당 어체중은 2주에 한번씩 측정하였고 8주간의 실험종료 후, 사료공급횟수, 성장률, 전어체 타우린농도와 일반성분을 분석하였다. 실험 1에서 타우린0.5, 1.0와 1.5% 실험구의 증쳬율, 일간성장률, 단백질효율이 대조구와 타우린 0.25% 실험구보다 유의적으로 높게 나타났다. 타우린 0.5% 실험구의 사료효율은 대조구, 타우린 0.25와 3.0% 실험구보다 유의적으로 높게 나타났다. 타우린 1% 실험구는 대조구보다 높은 전어체 조단백질 함량을 나타냈다. 반면, 타우린 1.5와 3% 실험구의 조지방함량은 대조구와 타우린 0.25%실험구보다 낮게 나타났다. 그러나 ANOVA 테스트에 의하면 치어기 돌돔에서의 성장개선과 어체내 지질함량을 감소시키기 위한 최적의 타우린 첨가수준은 0.5%이고 증체율의 broken-line 분석은 0.62%수준으로 나타났다. 실험 2에서 S+Tau0.25, S+Tau0.5 와S+Tau1.0 실험구의 성장은 대조구보다 유의적으로 높게 나타났다. 하지만 ANOVA 테스트에 의하면 사료 내 황아미노산이 존재할 때, 성장과 사료이용률에 긍정적 효과를 위한 최적의 타우린 첨가수준은 0.25%이고 증체율의 broken-line 분석은 0.3% 수준으로 나타났다. 전어체 단백질과 타우린 함량은 사료내 황아미노산의 수준이 높아짐에 따라 꾸준히 상승했다. 반면에, 전어체 지방함량은 사료내 타우린함량이 높아짐에 따라 유의적으로 낮아졌다. 그러므로 치어기 돌돔은 황아미노산으로부터 타우린합성을 잘 시키지 못 하는것처럼 보인다. 그러나 황아미노산을 어류 성장을 증진시키기 위해 실험구당3.3~3.8mg의 최적의 타우린 요구량에 첨가했을때, 이전 연구결과와 비교하여 약 50%의 타우린이 요구되었다. 이러한 결과들을 토대로, 치어기 돌돔은 사료내 g당 7mg의 타우린 요구량을 나타냈고, 황아미노산을 첨가했을 때 타우린 요구량은 3.8mg으로 줄었다. 따라서, 이러한 타우린요구량은 치어기돌돔은 황아미노산으로부터의 합성능력이 제한적인 것으로 보아진다.

This study was conducted in two parallel feeding trials to investigate the effects of dietary supplementation on growth performance in juvenile rock bream, Oplegnathus fasciatus (Experiment 1) and to evaluate whether methionine and cysteine would effectively spare taurine supplementation (Experiment 2). In both experiments, a fish meal based diet was used as a Control. In Exp 1, five experimental diets were prepared by adding taurine at 0.25%, 0.5%, 1.0%, 1.5% and 3.0% (Tau0.25, Tau0.5, Tau1.0, Tau1.5 and Tau3.0, respectively). In Exp 2, four experimental diets were prepared by adding fixed level of methionine and cysteine at 0.5%, and graded taurine at 0%, 0.25%, 0.5% and 1.0% (S+Tau0, S+Tau0.25, S+Tau0.5 and S+Tau1.0, respectively). Triplicate groups of 25 fish averaging 2.72 ± 0.04 g (mean ± SD) were fed one of the ten experimental diets. The experiments were carried out in a total of 30 aquariums (40-L) connected to an indoor semi-recirculation sea water system. In both experiments, the fish were hand-fed two times a day one of the formulated diets at a level of 4.0 - 3.0% of wet body weight day-1 on a dry-matter basis. Total fish weight per aquarium was determined biweekly and the amount of diet fed to the fish adjusted accordingly. After 8 weeks of feeding trials, growth performance, whole-body taurine concentration and proximate composition were measured. In trial 1, weight gain, specific growth rate and protein efficiency ratio of fish fed the Tau0.5, Tau1.0 and Tau1.5 diets were significantly higher (P < 0.05) than those of fish fed the Control and Tau0.25 diets. Feed efficiency of fish fed Tau0.5 was significantly higher than that of fish fed the Control, Tau0.25 and Tau3.0 diets. Fish fed Tau1.0 had higher whole-body crude protein content than fish fed the Control diet, while crude lipid content of fish fed the Tau1.5 and Tau3.0 diets was signifant lower than that of fish fed the Control and Tau0.25 diets. Although ANOVA test suggested that the optimum supplementation level of dietary taurine to improve growth and reduce body lipid in juvenile rock bream, O. fasciatus, could be 0.5% and a broken line analysis of weight gain indicated a level of 0.62%. In trial 2, growth performance of fish fed the S+Tau0.25, S+Tau0.5 and S+Tau1.0 diets were significantly higher (P < 0.05) than those of fish fed the Control diet. Although ANOVA test suggested that in the presence of sulfur amino acid in the diets, the optimum dietary taurine supplementation level could be 0.25% and broken line analysis of weight gain indicated a level of 0.3%, for positive effects on growth and feed utilization. Fish whole-body protein content and taurine concentration steadily increased with the increase of taurine dietary level in the presence of sulfur amino acid in the diets. On the other hand, whole-body lipid content significantly decreased with the incremental levels of dietary taurine. Therefore, juvenile O. fasciatus seems to have a low ability to synthesize taurine from sulful amino acid, however when sulfur amino acid were supplemented the optimum dietary taurine requirement to improve growth ranged from 3.3 to 3.8 mg taurine g diet-1, which represents a reduction of approximately 50% compared to our first experiment result. Based on these results, juvenile rock bream, O. fasciatus, have a dietary requirement of 7.0 mg taurine g diet-1, which was reduced to 3.8 mg taurine g diet-1 when 1% of sulfur amino acid were supplemented, this requirement for taurine may be due to a limited ability to synthesize it.