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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. [ABSTRACT FROM AUTHOR]

Abstract: An 11‐wk feeding trial was conducted to evaluate three different protein hydrolysates as feed ingredients in high‐plant‐protein diets for juvenile olive flounder. Five experimental diets were fed to juvenile olive flounder to examine the effect of three different protein hydrolysates on growth performance, innate immunity, and disease resistance against bacterial infection. A basal fishmeal (FM)‐based diet was regarded as a high‐FM diet (HFM) and a diet containing soy protein concentrate (SPC) as a substitute for 50% FM protein was considered as a low‐FM diet (LFM). Three other diets contained three different sources of protein hydrolysates, including shrimp, tilapia, and krill hydrolysates (designated as SH, TH, and KH), replacing 12% of FM protein. All diets were formulated to be isonitrogenous and isocaloric. Triplicate groups of fish (15.1 ± 0.1 g) were handfed one of the diets to apparent satiation twice daily for 11 wk and subsequently challenged against Edwardsiella tarda. Growth performance and feed utilization of fish fed hydrolysate‐supplemented diets were significantly improved compared to those of fish fed the LFM diet. Dietary inclusion of the protein hydrolysates significantly enhanced apparent digestibility of dry matter and protein of the diets. In the proximal intestine, histological alterations were observed in the fish fed the LFM diet. The fish fed the hydrolysate diets showed significantly longer mucosal fold and enterocytes and greater number of goblet cells compared to fish fed the LFM diet. Respiratory burst activity was significantly higher in fish fed the TH and KH diets than fish fed the LFM diet. Significantly higher immunoglobulin levels were found in fish fed SH and KH diets compared to those of fish fed the LFM diet. Dietary inclusion of the protein hydrolysates in SPC‐based diets exhibited the highest lysozyme activity. Significantly higher superoxide activity was observed in groups of fish fed the KH diet. Fish offered the protein hydrolysates were more resistant to bacterial infection caused by E. tarda. The results of this study suggest that the tested protein hydrolysates can be used as potential dietary supplements to improve growth performance and health status of juvenile olive flounder when they were fed a LFM diet. [ABSTRACT FROM AUTHOR]

Abstract: β‐Glucooligosaccharides (BGO), produced from barley β‐glucan, were used as a feed supplement (0.1%) for juvenile olive flounder (Paralichthys olivaceus) to identify and quantify its oral administration effects on innate immunomodulation and infectious disease protection. Juvenile flounders (14 ± 0.5 g) were divided into two groups fed either 0.1% BGO (treatment) or a standard diet (control) for 8 weeks. At the end of the experiment, investigation of the effects was carried out through systemic studies on growth performance, serum and mucus biochemical parameters, innate immunity, microvillus length, and relative pro‐inflammatory cytokine gene expression. The results demonstrated that the BGO diet produced slightly higher levels of growth performance, serum protein, microvillus length and pro‐inflammatory cytokine gene (tumour necrosis factor‐α, interleukin [IL]‐1β, and IL‐6) expression without any significant differences (p > .05). All innate immunity parameters were up‐regulated by BGO administration and, among these, respiratory burst, lysozyme and superoxide dismutase (SOD) were significantly different (p < .05). Fish in the both groups were challenged with Streptococcus iniae (1.35 × 108 CFU/ml), and BGO group was focused to confirm the promotion of innate immunity parameters. The results showed a significantly (p < .05) lower death rate compared with that of the control. Therefore, BGO could be used as a new prebiotic in future olive flounder aquaculture as well as to control streptococcosis. [ABSTRACT FROM AUTHOR]

The purpose of this study was to characterize the bacteria isolated from rockfish intestines and to investigate the effects of feed supplementation in rockfish aquaculture. Bacillus sp. KRF-7 isolated from the intestine of rockfish (Sebastes schlegelii) was demonstrated to be safe based on in vitro tests confirming the absence of hemolysis, cytotoxicity, and genes with toxigenic potential. In a feeding trial, providing a supplemental diet of 1 × 108 CFU g−1 Bacillus sp. KRF-7 was observed to positively alter the weight gain, specific growth rate, feed conversion ratio, and protein efficiency ratio of juvenile rockfish. KRF-7 supplementation showed positive regulation of nonspecific immune parameters, such as superoxide dismutase, lysozyme activity, and myeloperoxidase activity. This analysis also revealed a change in the composition of the intestinal microbiota at the phylum level from Proteobacteria to Firmicutes. In both the kidney and spleen, the expression levels of IL-10, NF-κB, and B cell activating factors in the KRF-7-supplemented group were significantly increased compared to those in the control group. Therefore, this study verified the safety of KRF-7 isolated from the intestine of rockfish and suggests that dietary supplementation with KRF-7 enhances the growth performance of rockfish and has beneficial effects on the regulation of the intestinal microbiota and immune response. • The probiotic properties of Bacillus sp. KRF-7 were investigated. • Dietary supplementation of KRF-7 upregulated the growth performance of rockfish. • Supplementation with KRF-7 modulated gut microbial community of rockfish. [ABSTRACT FROM AUTHOR]

Abstract Investigations were carried out to evaluate and quantify the effects of dietary supplementation with heat-killed (HK) Bacillus sp. SJ-10 (BSJ-10) probiotic (1 × 108 CFU g−1) on the growth and immunity of olive flounder (Paralichthys olivaceus). Flounder (averagely 9.64 g) were divided into two groups, and fed control and HK BSJ-10 (HKBSJ-10)-inoculated diets for 8 weeks. Investigations were carried out on growth and feed utilizations, innate immunity, serum biochemical parameters, microvilli length, and pro- and anti-inflammatory cytokine gene (tumor necrosis factor [TNF]-α, interleukin [IL]-1β, IL-6, and IL-10) transcriptions. Compared to control, HKBSJ-10 diet significantly (P < 0.05) enhanced weight gain and protein efficiency ratio, 1.17 and 1.11 folds respectively. Humoral innate immune parameters, lysozyme and superoxide dismutase in treatment group were also elevated by 1.34 and 1.16 folds. Similarly, an increased (P < 0.05) relative expressions of TNF-α, IL-1β, IL-6 were recorded in liver (2.71, 3.38, and 4.12 folds respectively), and gill (2.08, 1.98, and 1.81 folds respectively) than that of controls. Moreover, after challenge with Streptococcus iniae (1 × 108 CFU mL−1), the HKBSJ-10-fed group exhibited significantly higher protection (P < 0.05) against streptococcosis compared to controls, validating the observed changes in immune parameters and induction on the cytokine-encoding genes. Therefore, HKBSJ-10 increases growth, modulates innate immune parameters, and protects olive flounders against streptococcosis. Highlights • Heat killed Bacillus sp. SJ-10 (HKBSJ-10) positively improved growth and feed utilization in olive flounder. • HKBSJ-10 enhanced humoral innate immunity and pro-inflammatory cytokine transcriptions. • Administration of HKBSJ-10 could increase resistance against streptococcosis. [ABSTRACT FROM AUTHOR]

Abstract Bacillus sp. SJ-10 (BSJ-10) was identified from traditional Korean fermented fish, the previously recognized prebiotic β-glucooligosaccharides (BGO), and their combination as a synbiotic were prepared to evaluate their individual and synergistic effects in olive flounder (Paralichthys olivaceus). Four diets (one control and three treatments) were formulated containing neither BSJ-10 nor BGO (control), 1 × 108 CFU g −1 BSJ-10 (BSJ-10), 0.1% BGO (BGO), and 1 × 108 CFU g−1 BSJ-10 + 0.1% BGO (BSJ-10 + BGO). Triplicates of 15 fish (weight 10 ± 0.25 g) were randomly allocated to the four diet groups and fed one of the diets for 8 weeks. At the end of the experiment, fish weight gain (WG), specific growth rate (SGR), feed conversion ratio, and protein efficiency ratio in BSJ-10, BGO and BSJ-10 + BGO diets were positively modulated (P < 0.05) compared with control. Specially, WG and SGR were significantly (P < 0.05) higher in BSJ-10 + BGO than that of BSJ-10 and BGO (individual component). The innate immune parameters such as respiratory burst, superoxide dismutase, and lysozyme activity (LSZ) of fish fed BSJ-10 and BSJ-10 + BGO (both groups) were significantly (P < 0.05) higher than the control. Moreover, myeloperoxidase activity (MPO) and LSZ of fish fed BSJ-10 + BGO were significantly higher compared with individual component. Compared with control, intestinal BSJ-10 content, expression of interleukin (IL)-1β in liver and kidney, and tumor necrosis factor (TNF)-α in liver were higher in both groups, but microvillus length was increased (P < 0.05) only in BSJ-10 + BGO. During in vivo challenge experiment with Streptococcus iniae (1 × 108 CFU ml−1), survival rate of fish was significantly higher in all treatment groups versus control. Moreover, in BSJ-10 + BGO, protection against S. iniae infection and transcription of TNF-α and IL-6 in gill were significantly (P < 0.05) higher than the individual component. Collectively, an improved WG, SGR, MPO, LSZ, transcription of IL-6 and TNF-α, and cumulative survival rate against streptococcosis clearly demonstrates a synergistic outcome of diet BSJ-10 + BGO as synbiotic in olive flounder. Highlights • Bacillus sp. SJ-10 (BSJ-10) is identified as a potential probiotic in olive flounder. • BSJ-10+β-glucooligosaccharides produce synergistic effects on growth and innate immunity. • Transcription levels of pro-inflammatory cytokines are upregulated by dietary synbiotic. • Dietary synbiotic is able to increase microvillus length in the intestine. [ABSTRACT FROM AUTHOR]

Extrusion technology is known to enhance feed quality by controlling feed processing conditions. Although extrusion technology has been extensively used to improve livestock feed quality, research on its effects on quality in fish is lacking. Furthermore, studies on feed processing, the physical properties of feed produced using extruders, and the effects of extrusion on formulated feed quality remain scarce. Therefore, in this study, we investigated the effects of extrusion pressure and raw material particle size on the growth performance and digestive physiology of rockfish (Sebastes schlegeli). Experimental diets were prepared under different extrusion pressures by manipulating the screw speed [low pressure (LP), 1080 rpm/min; high pressure (HP), 620 rpm/min] and mean raw material particle sizes [small size (SS), 199.1 μm3; large size (LS), 1026.8 μm3] in a two-level factorial design. Four experimental diets (SS/LP, SS/HP, LS/LP, and LS/HP) were randomly assigned to 12 tanks (3 replicates), which were each stocked with 30 fish (initial mean body weight, 82.7 ± 0.2 g). After a 16-week feeding trial, observations showed that SS and LP enhanced fish weight gain and plasma growth-related hormone activity. In addition, SS and LP increased intestinal digestive activity in fish, positively affecting growth. These results indicate that manipulating physical pellet qualities by adjusting the feed ingredient extrusion pressure and raw material particle size can improve the growth performance and digestive physiology of rockfish, which should be considered in feed manufacturing. • Extrusion pressure and particle size improved rockfish growth rate and growth hormone activity. • Higher water absorption ability of feed was associated with better fish growth. • SS and LP enhanced fish weight gain and plasma growth-related hormone activity. • SS and LP increased the digestive activity of the intestines. [ABSTRACT FROM AUTHOR]

The effects of Bacillus sp. supplementation of different types of cells, such as spores and vegetative cells, on fish growth performance, intestinal microbial diversity alteration and immunity in juvenile olive flounder (Paralichthys olivaceus) were investigated. The fish were divided into three groups and provided with either a basal diet (control), Bacillus sp. vegetative cell (VCS) or spore (SS) supplemented diet for 8 weeks. At the end of the experiment, significant differences (P <.05) were found in terms of weight gain, specific growth rate, feed conversion ratio and protein efficiency ratio between the VCS and control groups. Respiratory burst, superoxide dismutase activity, and lysozyme activity, which are innate immune indicators, were observed with positive alterations (P <.05) in SS compared to controls. Intestinal microbial diversity analysis showed that the SS group had an increased richness estimate (Chao 1, ACE, and Jackknife) compared with the control group. Diversity estimates (Shannon and reverse Simpson) revealed that the VCS group was increased compared with the control group. Analyzing the similarity between groups through beta-diversity, Venn diagram, and heatmap analysis, the control and VCS groups were similar, and the SS group was different. IL-1β and TNF-α expression levels in the liver and spleen were increased in the SS group compared with the control group. In growth-related gene expression analysis, only growth hormone increased in the VCS group compared with the control group. In an in vivo challenge experiment with Streptococcus iniae (1 × 108 CFU/mL), the survival rates of the VCS and SS groups were 14.29% and 28.57%, respectively, when the control mortality reached 100%. Therefore, we concluded that supplementation of Bacillus sp. with different physiological processes affects the growth performance and immune activity of flounder. In particular, VCS can induce growth performance and growth-related gene expression, and SS can alter nonspecific immune and immune-related gene expressions. • The effect of dietary supplementation is affected by the Bacillus physiological process. • Dietary Bacillus vegetative cell supplementation improves growth performance. • Bacillus spore supplementation affects the intestinal microbial composition. • Nonspecific immunity is altered by Bacillus spore supplementation. • Pro-inflammatory cytokines are upregulated by dietary spore supplementation. [ABSTRACT FROM AUTHOR]