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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]

Butylated hydroxytoluene (BHT) is a commonly used antioxidant added to animal/fish feed to limit lipid autoxidation and peroxidation. Although there have been reviews and reports of BHT toxicity in animals, limited information is available with respect to the toxic effects and accumulation of BHT due to oral exposure in aquaculture species. Therefore, 120 days of feeding trial was conducted to evaluate the effects of dietary BHT on the marine fish olive flounder Paralichthys olivaceus. Graded levels of BHT were added to the basal diet in increments of 0, 10, 20, 40, 80, and 160 mg BHT/kg, corresponding to 0 (BHT0), 11 (BHT11), 19 (BHT19), 35 (BHT35), 85 (BHT85), and 121 (BHT121) mg BHT/kg diets, respectively. Fish with an average weight of 77.5 ± 0.3 g (mean ± SD) were fed one of the six experimental diets in triplicate groups. Growth performance, feed utilization, and survival rate were not significantly affected by the dietary BHT levels among all experimental groups, whereas BHT concentration in the muscle tissue was found to increase in a dose-dependent manner up to 60 days of the experimental period. Thereafter, BHT accumulation in muscle tissue showed a declining trend among all treatment groups. Furthermore, the whole-body proximate composition, nonspecific immune responses, and hematological parameters (except triglycerides) were not significantly influenced by the dietary levels of BHT. Blood triglyceride content was significantly higher in fish fed the BHT-free diet compared to all other treatment groups. Thus, this study demonstrates that dietary BHT (up to 121 mg/kg) is a safe and effective antioxidant without exhibiting any adverse effects on the growth performance, body composition, and immune responses in the marine fish olive flounder, P. olivaceus. [ABSTRACT FROM AUTHOR]

The present study examined the dietary substitution effect of chicken by‐product meal (CBM) for fish meal (FM) on growth, feed utilization, body composition, haematology and non‐specific immune responses of olive flounder, Paralichthys olivaceus. Six isonitrogenic and isolipidic experimental diets were prepared. The control (Con) diet contained 650 g/kg FM. One hundred, 200, 300, 400 and 500 g/kg FM were replaced with CBM, referred to as the CBM10, CBM20, CBM30, CBM40 and CBM50 diets, respectively. A total of 400 juvenile fish averaging 14.7 g was distributed into 20 tanks (20 fish/tank) and fed triplicate groups of each diet, except for quadruplicate groups for the Con and CBM30 diets twice daily to satiation for 8 weeks. Arginine, phenylalanine and threonine content of the experimental diets increased with dietary increased substitution of FM with CBM. The experimental diets did not affect survival, weight gain, specific growth rate, feed consumption and feed utilization of fish. The chemical composition, whole body amino acid profiles, haematological variables and non‐specific immune responses of fish were not changed by the experimental diets. These findings suggest that FM up to 500 g/kg can be substituted with CBM without retardation in growth, feed utilization, haematology and non‐specific immune responses of olive flounder. [ABSTRACT FROM AUTHOR]

The attractiveness of crude feed ingredients to olive flounder and effects of including feed ingredients showing strong feeding attractiveness in extruded pellet (EP) on performance of fish were determined. Four types of experimental EP were prepared to evaluate the effects of feed ingredient manipulation on performance of fish. Five per cent anchovy meal component of the control diet was substituted with an equal amount of jack mackerel meal, sardine meal and hydrolysed fish meal to create the JM, SM and HFM diets respectively. The diets were prepared in commercial form as EP. Jack mackerel meal produced the strongest feeding attractant responses of olive flounder, followed by sardine meal and hydrolysed fish meal. The greatest weight gain, feed consumption and condition factor (CF) were observed in fish fed the JM diet, followed by fish fed the SM, HFM and control diets, in that order in the 8‐week feeding trial. The dietary manipulation of feed ingredients performed in this study showed that the inclusion of ingredients with strong feeding attractiveness improved feed consumption and eventually accelerated the growth performance and CF of the fish. [ABSTRACT FROM AUTHOR]

Prebiotics, probiotics, and synbiotics are considered natural functional food ingredients and an alternative feeding strategy for immunomodulation and antibiotic eradication. Olive flounder (Paralichthys olivaceus) is commercially cultured in China, Japan, and Korea. Antibiotics used in flounder aquaculture produce antibiotic-resistant pathogens and residual effects on human. Prebiotics are non-digestible oligosaccharides, fermented by intestinal microbiota to produce short-chain fatty acids that bind G protein receptors. Probiotics are usually incorporated into the diet at a certain concentration to alter the intestinal microbial population through colonization or implantation. Synbiotics are combinations of prebiotics and probiotics that produce synergistically better benefits than separately. Previous studies on olive flounder have revealed that various types of immunostimulants, prebiotics, probiotics, synbiotics, and potentially immunoreactive feed additives can increase growth and feed utilization; cellular and humoral immunity; immune gene expression; blood/serum biochemistry; and infectious-disease resistance. Additive concentrations, their activity, and viability after feed storage and in the intestine, and interactions with the intestinal microbial community are major limiting factors. This review summarizes and discusses changes in growth and feed utilization, innate immunity, biochemical parameters, gene transcription, and disease protection in olive flounder after diet supplementation with various types of additives. It also indicates areas needing greater attention for future research. [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]

We evaluated the effects of diets incorporating the red algae Pyropia yezoensis, prepared by several different extraction methods, on the growth of juvenile Japanese flounder Paralichthys olivaceus. We assessed growth performance, as well as the levels of amino acids, fatty acids, insulin-like growth factor I (IGF-I) and interleukins (ILs). Four experimental diets were developed based on different methods of processing P. yezoensis. A commercial feed, laver powder (P), high-pressure heat extraction of laver (HPHE) and acid hydrolysis extraction of laver were used as the experimental diets. Three experimental replicates were established for each diet (40 fish/group, body weight 123.7 ± 1.1 g), and the fish were fed for 6 weeks. We found no significant differences in weight gain, specific growth rate or feeding efficiency among the groups ( P > 0.05); however, the fish fed HPHE had the greatest growth performance. Fish fed the laver extracts exhibited the highest protein efficiency ratio compared with the control and P groups. The experimental groups fed P. yezoensis extracts had significantly higher levels of IGF-I ( P < 0.05) than those of the control group. High levels of IL-2 were found in the P and HPHE groups, IL-12 in the HPHE group, and IL-6 in all experimental groups. Therefore, these results suggest that a P. yezoensis extract improved the growth performance and immunity of Japanese flounder. In particular, the high-pressure heating process was a useful extraction method for preparing a P. yezoensis extract, which had beneficial effects as a dietary supplement in Japanese flounder. [ABSTRACT FROM AUTHOR]

Abstract: This study was conducted to investigate the influence of dietary lipid level and supplemental soy lecithin on growth, feed utilization and body composition of juvenile flounder reared at two suboptimal water temperatures, 12 and 17 °C. Three isonitrogenous (CP 50%) diets containing 1% squid liver oil (S7), 7% squid liver oil (S14), and a mixture of 2% soy lecithin and 5% squid liver oil (SL14) were formulated to obtain 7% and 14% of crude lipid. Triplicate groups of fish (6.3±0.2 g) were fed to apparent satiation twice a day for 60 days. Weight gain, daily feed intake, feed efficiency and protein efficiency ratio were significantly higher for fish reared at 17 °C than at 12 °C. Daily feed intake was significantly decreased with the increase of dietary lipid level at the same water temperature, but weight gain was not affected by dietary lipid composition. At 12 °C, feed efficiency and protein efficiency ratio were significantly higher for fish fed the S14 and SL14 diets than those of fish fed the S7 diet, while at 17 °C feed efficiency and protein efficiency ratio of fish fed the S14 diet, which were not significantly different from those of fish fed the SL14 diet, were significantly higher than those of fish fed the S7 diet. There were no significant effects of dietary lipid composition or temperature range on the whole body contents of moisture, crude protein, lipid or ash. Dietary lipid composition and temperature affected the fatty acid content of the polar lipid from the liver; and the n-3HUFA contents such as 20:5n-3 and 20:6n-3 were higher at 12 °C than at 17 °C. The results of this study indicate that an increase of dietary lipid level from 7% to 14% has beneficial effects on feed utilization of flounder when reared in suboptimal water temperatures. The increase of water temperature from 12 to 17 °C improved growth and feed utilization, but 2% soy lecithin had no substantial effect on growth and feed efficiency of juvenile flounder. [Copyright &y& Elsevier]

A 12-week feeding trial was conducted to evaluate the effects of multi-strain probiotics (MSP) in a low fish meal (FM) diet on overall performance, gut microbiota, selected non-specific immune responses and antioxidant enzyme activities of olive flounder (Paralichthys olivaceus) juveniles. A total of 225 healthy olive flounders (initial mean body weight, 13.5 ± 0.01 g) were randomly separated into 3 groups of 75 fish, each group having three replicates of 25 fish; first group was fed with a FM-based control diet (Con), 2nd group was fed with a low-FM diet containing a blend of plant and animal protein meals replacing 30% of the FM protein (FM30), and 3rd group was fed with the FM30 diet supplemented with 108–109 CFU kg−1 of the MSP (Pro). With the exception of lipid retention, which was significantly lower in fish fed the FM30 diet compared to the other two treatments, no other statistically significant differences were recorded with respect to any of the other growth and nutrient utilization parameters. Myeloperoxidase and lysozyme activities of fish fed the Pro diet were much higher and significantly different than those of fish fed the FM30 diet. Glutathione peroxidase activity was significantly higher in Pro- than in Con-fed fish, which, in turn, was significantly higher than FM30-fed fish. Expression of immune-related genes including IL-1β, IL-6, and TNF-α was markedly upregulated in livers of the fish fed Pro diet compared to those fed the Con and FM30 diets. Furthermore, supplementation of MSP in FM30 diet enriched the Lactobacillus abundance in the fish gut as well as predictive gene functions in relation to lipid and carbohydrate metabolisms. These data suggested that the MSP could reduce the potential adverse effects of the low-FM diet and might be used as a healthy immunostimulant for olive flounder. • Low fishmeal diet (FM30) significantly affected the lipid retention of olive flounder. • The multi-strain probiotics (MSP) improved the activities of myeloperoxidase, lysozyme, and glutathione peroxidase. • The MSP supplement markedly upregulated the immune-related gene expression of IL-1β, IL-6, and TNF-α in the liver. • The MSP supplement enriched the predictive gene functions in relation to lipid and carbohydrate metabolisms. • The MSP could be used as a healthy immunostimulant for olive flounder. [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]

Abstract: Two studies were conducted to investigate the effects of dietary supplementation of three Bacillus spp. on growth performance, innate immunity and disease resistance of olive flounder against Streptococcus iniae and to examine the efficacy of Bacillus spp. on water quality reducing ammonia concentration and increasing fish survival. In the first experiment, a basal diet was prepared and regarded as a control and three other diets were prepared by supplementing one of three Bacillus spp. (B. subtilis, B. pumilus or B. licheniformis) at the dietary level of 0.5%. Triplicate groups of fish (initial body weight, 25g) were fed one of the four diets for eight weeks. Fish fed with B. subtilis containing diet showed significantly higher growth performance and feed efficiency than fish fed with the control diet. Also, significantly higher survival rates were observed in fish fed B. subtilis or B. pumilus containing diets during the feeding trial. Phagocytic activity was significantly increased in fish fed the probiotic containing diets and higher superoxide dismutase activity was observed in fish fed B. pumilus or B. licheniformis when compared to the control. However, serum lysozyme and myeloperoxidase activities did not significantly differ compared to the control. After a challenge with S. iniae, fish fed B. subtilis or B. licheniformis showed significantly higher survival rates compared to fish fed the control diet. In the second experiment, fish (30.1g) were fed a commercial diet for three weeks and then they were distributed to nine tanks at a density of 30 fish per tank (3 replicates per treatment). Fish were fasted for 5days in static water system, while one of two probiotics, B. subtilis or B. licheniformis was treated every 24h into the rearing water at the concentration of 104 CFUml−1. During the trial, significantly decreased ammonia concentration and fish mortality were observed by the supplementation of B. subtilis into the rearing water. The results in these studies indicate that B. subtilis has beneficial effects on growth performance, innate immunity and disease resistance of olive flounder and quality of the rearing water. [Copyright &y& Elsevier]

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]

The overall performance and well-being of juvenile olive flounder were evaluated in response to three isonitrogenous and isolipidic extruded feed pellets containing either wheat flour (WF), potato (PS) or corn starch (CS), as a dietary carbohydrate source. Following the 2-week acclimation period, triplicate groups of fish (16.6 ± 0.01 g) were assigned to each experimental diet and fed to apparent satiation for 8 weeks. The results of the extruded feed pellet's physical quality tests revealed that dietary inclusion of PS could significantly enhance the water stability of the extruded feed pellets. In addition, PS and CS diets had significantly higher bulk density than WF diet. Feeding juvenile flounders with these experimental diets, however, did not induce any significant changes in their overall performance. Significantly higher serum lysozyme activity was recorded in fish fed the PS and CS diets than those fed the WF diet. Fish fed the WF and CS diets had significantly higher superoxide dismutase activity than PS group. Expression of the immune-related genes, including SOD2, EPX-L, TNF-L, IL-6, and TIPRL, was notably up-regulated in liver of fish fed the PS and CS diets compared to those fed the WF diet. Interestingly, however, an inverse expression pattern was found for the same genes in the spleen where lower expression levels were detected in the PS and CS groups than the WF group. Overall, our findings revealed that while dietary utilization of PS produced an extruded feed pellet with markedly higher physical quality than either WF or CS, neither of these starch sources were able to significantly impact the flounder's performance. Further studies are needed to elucidate the potential long-term consequences of the invoked immune response in the PS and CS groups. • Overall performance and well-being of juvenile olive flounders were evaluated in response to the extruded feed pellets containing either wheat flour, potato starch or corn starch as dietary starch sources. • Diets containing potato starch showed significantly higher water stability than the other two experimental diets. • Dietary inclusion of either potato or corn starch in the extruded diet significantly affected immune-related genes expression in the liver and spleen of flounders. • The expression patterns of the target genes involved in the immune response were opposite in the liver and spleen after feeding with different starch sources. [ABSTRACT FROM AUTHOR]

This study was carried out to investigate the effect of dietary differences on intestinal microbial population alteration and its relationship to immune-related gene expression in juvenile olive flounder (Paralichthys olivaceus). Initially, flounder were divided into three groups and supplemented with fishmeal diet (FM), fishmeal replaced by plant protein (termed low-fishmeal (LFM)), and Bacillus sp. SJ-10 probiotic-inoculated LFM (Pro) for 4 weeks. At the start (Initial group) and after completing the feeding trial, intestines were subjected to microbiota analysis and immune-related gene expression. The results of the intestinal microbiota analysis demonstrated that the FM and LFM groups' microbial richness (Chao1, ACE, and Jackknife) and diversity (Shannon and Simpson) did not differ significantly (P >.05) compared to the Initial group. However, the Pro group exhibited increased (P <.05) richness compared to all other groups, but its diversity was lower than that of the Initial group. A similar alteration phenomenon was also found in community composition between these two groups. At the phylum level, the most abundant phylum was Proteobacteria for all groups, but the second most abundant phylum in the Initial and Pro groups was Bacteroidetes, whereas in the FM and LFM groups, it was Firmicutes. An additional analysis of genus-level community composition and prediction of functional composition analysis showed differences among the groups. In the intestine, the transcription of interleukin (IL)-10 and IL-1β was increased more in the LFM and Pro groups compared to the FM group. IL-6 was increased only in the Pro group, and tumor necrosis factor-α (TNF-α) gene expression did not differ significantly among the groups. Therefore, we concluded that dietary changes affect intestinal microbiota composition and immune-related gene expression; in particular, diets containing probiotics can lead to greater change during the same feeding period. • Dietary changes affect intestinal microbiota composition and immune-related gene expression of olive flounder. • Probiotic have a greater impact on intestinal microbial diversity and composition than changes in fishmeal content. • Feed composition changes and probiotic supplements can manipulate the intestinal microbiota of olive flounder. [ABSTRACT FROM AUTHOR]

In an eight-week feeding trial, encapsulated sodium butyrate (ESB), gamma-aminobutyric acid (GAB), selenium-yeast (SeY), yeast extract nucleotides (YEN), yucca meal (YUM), song-gang stone (SGS) and protease (PRT) were evaluated as functional feed additives in a low fishmeal (FM) diet for olive flounder Paralichthys olivaceus. Eight experimental diets were fed to 5.26 ± 0.17 g (mean ± SD) juvenile olive flounder in triplicates. A low-FM basal diet without feed additive was considered as control (CON); seven other diets were prepared by adding 4 g ESB, 158 mg GAB, 2 g SeY, 4 g YEN, 1.5 g YUM, 4 g SGS, and 175 mg PRT per kg of basal diet. Weight gain, specific growth rate, feed efficiency, and protein efficiency ratio of fish fed diets YEN, GAB, and SGS were significantly higher than those of fish fed CON diet (P <.05). Superoxide dismutase activity of fish fed YEN and myeloperoxidase (MPO) and nitroblue tetrazolium (NBT) of fish fed YEN, GAB, SGS, ESB, and YUM were significantly higher than those of fish fed CON diet. Whereas, there were no significant differences in non-specific immune responses among fish fed YEN, GAB, SGS, ESB, and YUM and diets (P >.05). Heat shock protein 70 gene expression of fish fed YEN and SeY was significantly higher than those of fish fed the CON diet. Intestinal villi length of fish fed YEN, GAB, SGS, and ESB was significantly higher than those of fish fed CON. Also, intestinal trypsin activity of fish fed YEN, GAB, SGS, ESB, and PRT was significantly higher than those of fish fed CON diet (P <.05). After seven days of challenge test, fish fed diets YEN, GAB, SGS, PRT, and YUM had higher cumulative survival than those of fish fed CON diet. In conclusion, YEN, GAB, and SGS could have beneficial effects on growth and feed utilization performance, MPO and NBT activity, intestinal villi length, intestinal trypsin activity, and cumulative survival of olive flounder fed low-FM diets. • Functional feed additives such as YEN, GAB, and SGS can enhance growth performance of olive flounder • YEN, GAB, and SGS improved intestinal villi length, trypsin activity, non-specific immune responses, and disease resistance • Selective functional feed additives (YEN, GAB, and SGS) can be considered cost-effective solutions in low fish meal diets [ABSTRACT FROM AUTHOR]