Study on dietary essential amino acid requirements of red sea bream (Pagrus major) and olive flounder (Paralichthys olivaceus)

Abstract

In the first experiment (chapter 2), a 12-week feeding trial was conducted to determine dietary valine requirement of red sea bream. Six diets were formulated with graded levels of valine (0.27, 0.79, 1.22, 1.69, 2.04 and 2.38% diet) and fed to triplicate groups of fish (32.04 ± 0.2 g) to apparent satiation. Significantly higher growth and feed utilization were obtained at valine levels of ≥0.79%. Non-specific immune responses of fish were significantly improved by increment of dietary valine up to 2.04%. Significantly lower postprandial ammonia excretion levels were obtained at higher valine levels. The optimum valine requirement level was estimated at 0.9% of diet. The second experiment (chapter 3), was undertaken to evaluate dietary arginine requirement of red sea bream (13.3 ± 0.2 g). Six diets were prepared to contain 1.2, 1.6, 2.0, 2.4, 2.8 and 3.2% arginine, and fed to triplicate groups of fish (13.3 ± 0.2 g) to apparent satiation for 9 weeks. Fish fed ≥ 2.0% arginine showed significantly higher growth than those fed 1.2% arginine. Significant improvement in protein productive value was found at 2.4% arginine. Fish hematology was influenced by arginine levels. Significant improvement in fish innate immunity was found at increased arginine levels. The optimum dietary arginine level was estimated to be 2.54% of diet. The third experiment (chapter 4) was carried out to quantify isoleucine requirement of olive flounder. Six experimental diets were formulated to contain graded levels of isoleucine (0.48, 0.87, 1.43, 1.94, 2.37 and 2.78% diet) and fed to triplicate groups of fish to apparent satiation for 9 weeks. The highest growth was obtained at 1.43% isoleucine. The results showed the significant increase of plasma total protein and cholesterol concentrations at higher isoleucine levels. Significant reductions in plasma alanine aminotransferase and aspartate aminotransferase activities were detected by increment of isoleucine level. Fish innate immunity was significantly enhanced at increased isoleucine levels. Dietary isoleucine requirement was estimated to be 1.69% of diet. The forth experiment (chapter 5) was conducted to quantify dietary methionine requirement of olive flounder. Six diets were formulated to contain graded levels of methionine from 0.3 to 1.8% and fed to triplicate groups of fish (17.28±0.1 g) to apparent satiation for 8 weeks. Fish fed ≥1.5% methionine exhibited significantly higher growth than those fed 0.3% methionine. Increment of dietary methionine level resulted in a numerical increase of most whole-body essential amino acids. The optimal dietary methionine level was suggested to be 1.63% diet. Finally, in the last experiment (chapter 6), utilization efficiency of free lysine (FL) and dipeptide lysine-glycine (LG) was compared in diets for olive flounder. A basal experimental diet contained 0.5% lysine from fish meal and four other diets were prepared by supplementing 0.5 or 1.0% of either FL or LG. The fish (5.41±0.16 g) were fed one of the diets at the rate of 3% BW/day for six weeks. The lowest weight gain was found in fish fed the basal diet and differed significantly from that of others. The results of two-way ANOVA showed that both lysine level (P = 0.001) and type (P = 0.034) influence fish weight gain. Also, the results revealed the significant improvement of protein efficiency ratio (PER) by increment of dietary lysine level, and the groups fed LG supplemented diets showed higher PER values. Significantly higher whole-body arginine level was found in LG fed groups. Whole-body valine and aspartic acid contents were affected by lysine level. Our findings showed that juvenile olive flounder can utilize LG more efficiently than FL for protein synthesis.