This study was conducted to determine dietary threonine (Thr) requirement for juvenile olive flounder (Paralichthys olivaceus). A total of 450 juvenile fish (23.2 ± 0.4 g) were randomly distributed to 18 tanks (215 L) with 25 fish per tank. Experimental diets included with graded levels of Thr at 0.0%, 0.4%, 0.8%, 1.2%, 1.6%, and 2.0% were assigned for triplicate groups of fish and fed two times daily to apparent satiation for 12 weeks. Weight gain, specific growth rate, feed intake, feed utilization and survival were significantly (p < 0.05) increased in fish fed with dietary Thr levels over 0.8%, and no significant differences were observed between 0.8% to 2.3% levels. Non-specific immune parameters of serum lysozyme, myeloperoxidase activity, antiprotease activity, and total immunoglobulin were significantly increased by dietary Thr over 0.8%. Based on the broken-line regression analysis, the Thr requirement for the optimum growth and immune response in olive flounder is likely to be 1.03% in the diet.

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A twelve-week feeding trial was conducted to investigate the effect of dietary supplementation of a functional immunostimulant mixture (FIM; nucleotides, β-glucan and vitamins C and E) on growth, feed utilization, innate immunity, digestive enzyme activity, hematological parameters, intestinal morphology and inflammatory gene expressions of olive flounder, Paralichthys olivaceus. A fish meal-based basal diet (control) was formulated, and three other diets were prepared by incorporating 0.5, 1.0 and 1.5% FIM into the basal diet (HB0.5, HB1.0 and HB1.5, respectively). Five replicate groups of fish (26.3 ± 0.1 g) were fed one of the experimental diets. Inclusion of 1.5% FIM in the diet significantly enhanced growth and feed utilization. Significantly higher plasma hemoglobin, hematocrit, total protein levels and lower plasma glucose level were observed in the HB1.5 group. Total immunoglobulin content, lysozyme, nitroblue tetrazolium, myeloperoxidase, superoxide dismutase, glutathione peroxidase and catalase activities and immune-related gene expressions of toll-like receptor and perforin were significantly increased at the highest inclusion level. FIM supplementation significantly increased villus height and goblet cell counts. Anti-inflammatory gene expressions were significantly upregulated at a 1.5% level. Dietary supplementation of 1.5% of FIM could improve growth and feed utilization, immune, hematological and intestinal histomorphological parameters of olive flounder.

This study analyzed the expression of growth-related genes of olive flounder, Paralichthys olivaceus, fed a low-fish meal (FM) diet to investigate the replacement of the FM diet in the field. The expression of growth hormone (GH)/insulin-

A supplemental effect of Achyranthes aspera extract (200 mg/kg phytosterol) in diets was evaluated for Pacific white shrimp (Penaeus vannamei) on growth performance, digestibility, innate immunity, antioxidant capacity, and disease resistance against Vibrio parahaemolyticus. A fish meal and soybean meal‐based control diet (Con; protein 38.0% and lipid 8.7%) was formulated and five other diets were prepared by adding A. aspera extract into Con diet to be 0.05, 0.1, 0.2, 0.4, and 0.8 mg phytosterol/kg concentration (designated as P05, P10, P20, P40, and P80, respectively). Three replicate groups of 30 shrimp (initial body weight, 0.40 ± 0.001 g) per diet were randomly assigned into 18 acrylic tanks (240 L) and fed one of the diets for 53 days. The growth performance and feed utilization efficiency were significantly higher in shrimp fed P20 and P80 diets than in shrimp fed Con and P10 diets. The dietary phytosterol supplementation improved non‐specific immune response, antioxidant capacity, and apparent digestibility coefficients of dry matter and protein of shrimp. The IGF‐binding protein gene expression was also upregulated with dietary phytosterol supplementation. During the challenge test, the disease resistance of shrimp was significantly enhanced against V. parahaemolyticus when shrimp were fed P20 diet. These results indicate that A. aspera extract could be used as a functional feed additive for the improvements in the growth performance, feed efficiency, innate immunity, antioxidant capacity, digestibility, and disease resistance of the shrimp. The optimum dietary inclusion level of the phytosterol seems to be 0.2–0.4 mg/kg diet.