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A ten-week culture trial in juvenile large yellow croaker (Larimichthys crocea) (10.80 ± 0.10 g) was conducted to assess the impact of supplementing heat-killed Lactobacillus acidophilus (HLA) on growth performance, intestinal digestive enzyme activity, antioxidant capacity and inflammatory response. Five iso-nitrogenous (42 % crude protein) and iso-lipidic (12 % crude lipid) experimental feeds with different levels of HLA (0.0 %, 0.1 %, 0.2 %, 0.4 %, or 0.8 %) were prepared. They were named FO (control group), HLA0.1, HLA0.2, HLA0.4 and HLA0.8, respectively. The results indicated that HLA addition had no impact on survival (P > 0.05). In this experiment, the final body weight, weight gain rate and specific growth rate showed a quadratic regression trend, initially increasing and subsequently decreasing with the increasing in HLA levels, and attained the peak value at 0.2 % HLA supplemental level (P < 0.05). In contrast to the control group, in terms of digestive ability, amylase, lipase and trypsin exhibited a notable linear and quadratic pattern, demonstrating a substantial increase when 0.1% 0.2 % HLA was added in the diets (P < 0.05). Notably, elevated levels of catalase (CAT) activity, superoxide dismutase (SOD) activity, and total antioxidant capacity (T-AOC) were observed in the liver when adding 0.1%–0.2 % HLA, and the level of malondialdehyde (MDA) was significantly decreased and the liver exhibited a notable upregulation in the mRNA expression levels of nrf2 , cat , sod2 , and sod3 (P < 0.05). Additionally, the mRNA levels of genes associated with tight junctions in the intestines (zo-1 , zo-2 and occludin) exhibited a significant upregulation when 0.2 % HLA was added in the feed (P < 0.05). Furthermore, the levels of mRNA expression for proinflammatory genes in the intestines including tnf-α , il-1β , il-6 and il-8 exhibited a quadratic regression trend, characterized by an initial decline followed by subsequent growth (P < 0.05). Meanwhile, the levels of mRNA expression for genes linked to anti-inflammatory responses in the intestines (including il-10 , tgf-β , and arg 1) exhibited a quadratic regression pattern, initially increasing and subsequently decreasing (P < 0.05). Compare with the control group, the levels of tnf-α , il-1β and il-8 expression were notably downregulated in all HLA addition groups (P < 0.05). When 0.2 % HLA was added, the expression levels of il-10 , tgf-β and arg 1 in the intestinal tract were markedly increased (P < 0.05). Overall, the supplementation of 0.2 % HLA in the feed has been shown to enhance the growth performance. The enhancement was attributed to HLA's capacity to improve antioxidant function, intestinal barrier integrity, and mitigate inflammatory responses. This research offers a scientific foundation for the utilization of HLA in aquaculture. • Growth performance of large yellow croaker was enhanced when heat-killed Lactobacillus acidophilus was added to the diet. • Dietary supplementation with 0.2 % HLA can enhance the antioxidant capacity and liver digestive enzyme activities in large yellow croaker. • Dietary supplementation with 0.2 % HLA can enhance the intestinal barrier and inflammatory response in large yellow croaker. [ABSTRACT FROM AUTHOR]

An 8-week growth trial was performed to investigate the protective effects of methanotroph bacteria meal (MBM) produced from methane against soybean meal-induced enteritis (SBMIE) in juvenile turbot (Scophthalmus maximus L.). Five isonitrogenous and isolipidic diets were formulated: fishmeal-based diet (FM, the control group); FM with approximate 50% of fishmeal substituted by 399.4 g/kg soybean meal (SBM); SBM supplemented with 63.6, 127.2 and 190.8 g/kg MBM (named MBM1, MBM2 and MBM3), each diet was randomly assigned to triplicate fibreglass tanks. Results showed that fish fed with SBM exhibited enteritis, identified by reduced relative weight of intestine (RWI), as well as expanded lamina propria width and up-regulated gene expression of pro-inflammatory cytokines (tnf-α , il-6 and il-8) in intestine. While the above symptoms were reversed when diet SBM supplemented with MBM at the levels of 63.6 and 127.2 g/kg, as well as characterized by up-regulated gene expression of anti-inflammatory cytokines (tgf-β and il-10) and tight junction protein (claudin3 , claudin4 and claudin7) in intestine. Intestinal transcriptome analysis showed that the differentially expressed genes between groups FM and SBM predominantly enriched in the JAK-STAT signaling pathway, and the enrichment of differentially expressed genes between groups SBM and SBM supplemented with 63.6 g/kg MBM was in the inflammatory bowel disease (IBD) and JAK-STAT signaling pathway. To be specific, the expression of jak1 , jak2b , stat1 and stat5a was significantly up-regulated when fish fed with SBM, suggested the activation of JAK-STAT signaling pathway, while the expression of these above genes was depressed by providing MBM to diet SBM, and the gene expression of toll-like receptors tlr2 and tlr5b showed a similar pattern. Moreover, intestinal flora analysis showed that community richness and abundance of beneficial bacteria (Cetobacterium and acillus_coagulans) were improved when fish fed with SBM supplemented with 63.6 g/kg MBM. Overall, methanotroph bacteria meal may alleviate SBMIE by regulating the expression of tight junction protein, toll-like receptors and JAK-STAT signaling pathway, as well as improving intestinal flora profile, which would be beneficial for enhancing the immune tolerance and utilization efficiency of turbot to dietary soybean meal. • Methanotroph bacteria can improve feed efficiency ratio, intestinal morphology and anti-inflammatory cytokines expression. • Methanotroph bacteria alleviated soybean meal-induced enteritis by inhibiting TLRs and JAK-STAT signaling pathway. • Methanotroph bacteria would improve intestinal flora composition when turbot fed diet with high levels of soybean meal. [ABSTRACT FROM AUTHOR]

Abstract: This experiment investigated the effects of dissolved oxygen (DO) on the survival and immune responses of scallop Chlamys farreri. The scallops (initial mean dry weight of soft tissue 1.52±0.10g) were cultivated in the seawater with different DO levels (8.5, 6.5, 4.5, and 2.5mgl−1, respectively) for 21d. Each treatment had triplicate groups of 35 animals. During the experimental period, the scallops were fed with Spirulina maxima, and water temperature ranged from 15.2°C to 17.5°C, salinity from 29.5‰ to 32.5‰ and pH from 7.5 to 8.2. Survival, specific growth rate (SGR) and total haemocyte count (THC) were examined at the end of the study, and superoxide dismutase (SOD), acid phosphatase (ACP) and alkaline phosphatase (ALP), were examined at 12h, 24h, Day 7, Day 14 and Day 21 after being exposed to the graded DO levels. The lower DO levels (2.5 and 4.5mgl−1) resulted in lower survivals of scallops, and the survival (81.7%) at 2.5mgl−1DO was significantly lower than those (100.0%) at 8.5 and 6.5mgl−1 DO. Similarly, the SGR and THC of scallop gradually reduced with decreasing DO levels, and reached significant levels at 2.5mgl−1 DO (P <0.05). At higher DO levels (8.5 and 6.5mgl−1), the SOD activity maintained rather stable during the entire sampling period. At lower DO levels (4.5 and 2.5mgl−1), however, the SOD activity significantly increased at 12h, and then significantly decreased to the levels below the normal. At the two lower DO levels, ACP activities had no significant changes before Day 7, and then declined to the levels that were significantly lower than the normal. Significantly higher ALP activity was only observed at 12h in the treatment of 2.5mgl−1 DO, but in all other treatments and sampling times it fluctuated in a narrow range. In conclusion, less than 4.5mgl−1 DO reduced the survival and depressed the immune responses of C. farreri. [Copyright &y& Elsevier]