An 8-week feeding trial was conducted to evaluate the effects of dietary γ-aminobutyric acid (GABA) on growth performance, immune response, and disease resistance for juvenile whiteleg shrimp, Litopenaeus vannamei. Five isonitrogenous diets were formulated by supplementing 0 (CON), 50 (GABA₅₀), 100 (GABA₁₀₀), and 300 (GABA₃₀₀) mg of GABA and 4 g of oxytetracycline (OTC) per kilogram of diet. A total of 225 juvenile whiteleg shrimp with an initial weight of g were randomly distributed and reared in 15 aquaria as triplicates. After 8 weeks of the feeding trial, weight gain, specific growth rate, feed efficiency, and protein efficiency ratio of shrimp fed GABA₁₀₀ were significantly higher than those of shrimp fed CON, GABA₅₀, and GABA₃₀₀ diets ( ). However, there were no significant differences among shrimp fed CON, GABA₅₀, GABA₃₀₀, and OTC diets ( ). After nine days of challenge test with Vibrio alginolyticus, the average cumulative survival rate of shrimp fed GABA₅₀, GABA₁₀₀, and OTC was significantly higher than that of shrimp fed GABA₃₀₀ and CON diets ( ). These results may suggest that 100 mg dietary GABA supplementation (including endogenous GABA, 175.6 mg/kg diet) per kilogram of diet could be the optimum dietary level to replace antibiotics and improve growth performance and disease resistance in whiteleg shrimp L. vannamei.

Gamma-aminobutyric acid (GABA) is a non-protein amino acid that is found in the brain and central nervous system of animals as an inhibitory neurotransmitter. It has been shown to have a variety of physiological functions, including stress reduction and immune enhancement. This study investigated the effects of dietary supplementation with GABA on growth, serum biochemistry, innate immunity, and disease resistance in juvenile olive flounders (Paralichthys olivaceus) challenged with Edwardsiella tarda under high-stocking density. A control diet and three experimental diets were prepared, with 150 mg/kg (GABA150), 200 mg/kg (GABA200), and 250 mg/kg (GABA250) of GABA added to each diet, respectively. Each experimental diet was fed to olive flounders in triplicate with an initial weight of 12.75 g ± 0.3 g in 40 L tanks at two stocking densities: normal density (20 fish/tank) and high density (40 fish/tank). After 8 weeks of the feeding trial, growth, feed utilization, whole-body proximate compositions, blood analyses, and non-specific immune responses were measured, and challenge tests were performed. There were no significant differences in the weight gain (WG) and specific growth rate (SGR) among fish fed the GABA-supplemented diets at the two stocking densities. However, the normal-density groups showed significantly higher WG and SGR than the high-density groups (p < 0.05). There was no significant difference in feed efficiency and protein efficiency ratio among all groups. Moreover, there was no significant difference in the whole-body proximate composition analysis (p > 0.05). There were no significant differences in cortisol levels in fish fed the GABA at both densities, but the high-density group showed a significantly higher cortisol than the low-density group. Blood GABA significantly increased in a dose-dependent manner regardless of the density groups (p < 0.05). Superoxide dismutase activity showed significantly higher levels than the control group, but there was no significant effect of the stocking densities in fish fed the GABA diets (p < 0.05). Myeloperoxidase activities in fish fed the GABA200 and GABA250 diets showed significantly higher levels at both of the stocking densities (p < 0.05). Lysozyme activity was significantly higher in the GABA150 group than in the CON, GABA200, and GABA250 groups (p < 0.05). After 15 days of challenge tests with Edwardsiella tarda, the cumulative survival rates of the GABA150, GABA200, and GABA250 groups were significantly higher than that of the CON group (p < 0.05). The results suggested that the optimal dietary GABA level for juvenile olive flounder culture is 150 mg/kg, regardless of rearing density, to enhance growth, immunity, and disease resistance.

Aquaculture is an important source of food for the growing global population. To meet the increasing demand for fish, intensive aquaculture methods are commonly used. However, these methods can lead to stress and disease in fish, which can result in significant economic losses. Gamma-aminobutyric acid (GABA) is a non-protein amino acid that is found in the brain and central nervous system of animals as inhibitory neurotransmitter. It has been shown to have a variety of physiological functions, including stress reduction and immune enhancement. This study investigated the effects of dietary supplementation of GABA on growth, serum biochemistry, innate immunity and disease resistance in juvenile olive flounder (Paralichthys olivaceus) challenged with Edwardsiella tarda under high stocking density. A control diet and three experimental diets were prepared, with 150 mg/kg (GABA150), 200 mg/kg (GABA200), and 250 mg/kg (GABA250) of GABA added to each diet, respectively. The actual GABA content of the experimental diets was analyzed and found to be 63.9 mg/kg (CON), 231.3 mg/kg (GABA150), 291.6 mg/kg (GABA200), and 323.9 mg/kg (GABA250). Each experimental diet was fed to olive flounder with an initial weight of 12.75 g ± 0.3 g in 40 L tanks at two stocking densities: normal density (20 fish/tank) and high density (40 fish/tank). The experiment was conducted in triplicate for each diet and stocking density. The water temperature was maintained at 17.5 ± 1℃ and the salinity at 33 ± 1 ppt. After 8 weeks of feeding trial, growth, feed utilization, whole-body proximate composition, blood analysis, non-specific immune response, and challenge test were performed. There were no significant difference in weight gain and specific growth rate among the GABA concentrations and density × GABA concentration interaction groups. However, the low-density groups showed significantly higher values than the high-density groups (P < 0.05). There was no significant difference in feed efficiency and protein efficiency ratio among all groups. Moreover, there was no significant difference in the whole-body general composition analysis (P > 0.05). In the hematological analysis, there was no significant difference in cortisol in terms of diet and density × GABA concentration interaction, but the high-density experimental group showed a significantly higher value. Blood GABA significantly increased in proportion to the addition amount regardless of the density group (P<0.05). Superoxide dismutase activity in the non-specific immune response showed that the GABA-added experimental group had a significantly higher value than the control group, but there was no significant effect of the density densities or density × GABA concentration interaction (P<0.05). Myeloperoxidase activities in fish fed the GABA200 and GABA250 diets showed significantly higher values, and a density × GABA concentration interaction effect was observed (P<0.05). Lysozyme activity was significantly higher in the GABA150 group than in the CON, GABA200, and GABA250 groups (P < 0.05). After 15 days of challenge test by intraperitoneal injection of Edwardsiella tarda, the cumulative survival rates of the GABA150, GABA200, and GABA250 groups were significantly higher than that of the CON group (P < 0.05). The results suggested that the optimal dietary GABA level for juvenile olive flounder culture is 150 mg/kg, regardless of rearing density, to enhance growth, immune function and disease resistance.

The drastic surge in Sardine landings in Korea underscores the urgent need for sustainable upcycling strategies. However, research on the feasibility of using sardine (SD) in food waste (FW)-based substrates during the cultivation of black soldier fly (Hermetia illucens) larvae (BSFL) remains limited. Thus, we aimed to investigate the effect of incorporating varying SD contents (0, 25, 50, 75, and 100%), into which 4-day-old (third-instar) larvae weighing approximately 0.02 g were introduced and reared for 12 days in triplicate. SD inclusion in the substrate had a dose-dependent effect on BSFL growth; higher concentrations (≥50%) markedly inhibited key growth indices, including a significant reduction in total biomass (p < 0.05). Incorporating SD into the diet dose-dependently enriched the biomass with eicosapentaenoic acid and docosahexaenoic acid while reducing the relative proportions of saturated and monounsaturated fatty acids (p < 0.05). Proteobacteria and Firmicutes were the dominant phyla in the intestinal microbiota of BSFL. Further, SD inclusion altered the gut microbial community structure. Increased SD concentration in the diet led to a progressive reduction in unique genera, indicating decreased microbial diversity at higher inclusion levels. Overall, incorporating SD into FW for BSFL cultivation is feasible; however, optimizing substrate composition—particularly moisture and nutrient balance—is necessary to enhance larval growth and productivity.

Fisheries and Aquatic Sciences