This study investigates the effect of dietary Lactobacillus plantarum supplementation on juvenile coho salmon (Oncorhynchus kisutch). Four groups of the juveniles (initial weight 103.87 ± 2.65 g) were fed for 10 weeks with four diets containing 0 (control diet), 10⁵ (T1), 10⁷ (T2), and 10⁹ (T3) cfu/g of L. plantarum. The main results are as follows: Compared with the control diet, the final weight, specific growth rate (SGR), and weight gain rate (WGR) of the juveniles fed the T1, T2, and T3 diet significantly (p < 0.05) increased, while the feed coefficient ratio (FCR) expressed an opposite trend. The activities of superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-PX) in the serum of the juveniles fed the T2 diet significantly (p < 0.05) increased, while the malondialdehyde (MDA) expressed an opposite trend. The expression of phosphatidylinositol 4,5-bisphosphate 3-kinase (pi3k), AKT-interacting protein (akt), mechanistic target of rapamycin kinase (mtor), glucose-6-phosphate dehydrogenase (g6pd), sod, cat, and gsh-px genes in the liver of the juveniles fed the T2 diet significantly (p < 0.05) increased. In conclusion, the T2 diet significantly improved the growth performance, antioxidant capacity, and upregulated key mTOR pathway genes in juvenile coho salmon.

Mannan oligosaccharide (MOS), a prebiotic derived from yeast cell walls, has been shown to enhance growth performance and health status in various aquatic species. As an exogenous antigen adjuvant, MOS modulates T-cell-mediated immune responses, thereby improving immune function and suppressing excessive inflammatory reactions. This study aimed to evaluate the effects of dietary MOS supplementation on growth performance, serum biochemical parameters, muscle composition, digestive enzyme activity, antioxidant and immune status, and the mTOR signaling pathway in juvenile GIFT tilapia (Oreochromis niloticus). Juveniles (initial body weight: 16.17 ± 1.32 g) were randomly assigned to six treatment groups (three replicate tanks per group) and fed diets supplemented with MOS at 0, 0.2%, 0.4%, 0.6%, 0.8%, and 1% (equivalent to 0, 2, 4, 6, 8, and 10 g/kg of diet, respectively) for 60 days. Compared with the control group, fish fed MOS-supplemented diets exhibited significantly higher (p < 0.05) weight gain rates, specific growth rates, and protein efficiency ratios, along with a significantly lower (p < 0.05) feed conversion ratio. Serum albumin, high-density lipoprotein, and lysozyme levels were significantly increased (p < 0.05), whereas triglycerides, low-density lipoprotein, aspartate aminotransferase, and alanine aminotransferase levels were significantly decreased (p < 0.05). In the liver, head kidney, and spleen, the expression of pro-inflammatory genes (tumor necrosis factor α, interleukin 1β, interleukin 6, interleukin 8, and interferon γ) was significantly downregulated (p < 0.05), while the expression of antioxidant and protective genes (superoxide dismutase, catalase, glutathione peroxidase, glutathione S-transferase, nuclear factor erythroid 2-related factor 2, lysozyme, alkaline phosphatase, interleukin-10, transforming growth factor β, and heat shock protein 70) as well as mTOR signaling pathway-related genes (mammalian target of rapamycin, akt protein kinase B, phosphatidylinositol 3 kinase, and ribosomal protein S6 kinase polypeptide 1) was significantly upregulated (p < 0.05). Overall, MOS positively affects tilapia’s growth, health, and immunity, with 0.60% identified as the optimal dietary level based on growth performance.

Intestinal oxidative imbalance, inflammatory activation, and microbial dysbiosis are increasingly recognized as major factors affecting the health status of intensively cultured largemouth bass (Micropterus salmoides). Chlorogenic acid (CGA) is a plant-derived polyphenolic compound that is well known for its antioxidant and anti-inflammatory properties. Although its inclusion as a dietary supplement in aquafeeds has garnered increasing interest, its effects on intestinal health in largemouth bass under normal rearing conditions remain largely unknown. Hence, the present investigation was designed to elucidate how incrementally elevated dietary CGA concentrations modulate oxidative capacity, inflammatory gene expression, mucosal histological features, and enteric microbiota structure in juvenile largemouth bass. In this study, largemouth bass were fed diets containing 0, 200, 400, or 600 mg/kg CGA for 70 days, and we evaluated intestinal antioxidant capacity, inflammation-related transcriptional responses, histomorphology, and gut microbiota were assessed. The results demonstrated that CGA supplementation significantly raised intestinal total antioxidant capacity as well as the activities of superoxide dismutase, catalase, glutathione peroxidase, and glutathione reductase, while substantially decreasing malondialdehyde levels (p < 0.05). The transcription levels of cat, gsh-px, gst, sod, nrf2, and ucp2 were markedly upregulated, whereas keap1 expression was downregulated (p < 0.05). CGA supplementation also reduced the transcription levels of several proinflammatory genes, including il-1β, il-6, il-8, tnf-α, nf-κb, p50, map3k, jak2, as well as stat3, while significantly elevating il-10 expression, in the 200 and 400 mg/kg groups, tgf-β expression was also lowered (p < 0.05). Histological examination revealed that CGA supplementation influenced intestinal morphology in a dose-dependent manner; the most consistent improvements in villus length, villus width, and muscularis thickness occurred at the 400 mg/kg level, whereas the 600 mg/kg level showed weaker effects in several parameters compared with the control. Furthermore, 16S rRNA sequencing indicated that CGA altered microbial diversity, community structure, and predicted functional profiles in the intestine. In summary, dietary CGA supplementation was associated with enhanced intestinal antioxidant capacity, modified inflammation-related transcriptional responses, changes in intestinal morphology, and shifts in the gut microbial community of largemouth bass. Within the tested dose range, the 400 mg/kg group exhibited relatively favorable responses in several measured indicators under the present experimental conditions.

Probiotics are considered promising feed additives for enhancing fish health and production performance in aquaculture. This study evaluated the effects of dietary supplementation with Sporolactobacillus laevolacticus on growth performance, feed utilization, intestinal health, and physiological responses in juvenile coho salmon (Oncorhynchus kisutch). Fish were fed a control diet or diets supplemented with S. laevolacticus at 0.89 × 10⁷, 0.90 × 10⁹, or 0.87 × 10¹¹ CFU/g for 10 weeks. Compared with the control, S. laevolacticus supplementation significantly increased final body weight, weight gain rate, specific growth rate, and protein efficiency ratio, while decreasing the feed conversion ratio (p < 0.05). It also significantly enhanced intestinal protease and α-amylase activities, improved serum biochemical and immune-related parameters, and promoted better intestinal morphology (p < 0.05). Additionally, S. laevolacticus supplementation led to elevated expression of antioxidant-related genes, reduced expression of pro-inflammatory genes, and altered gut microbial composition, characterized by a decrease in Proteobacteria and increases in Firmicutes and Lactobacillales. Among the tested dosages, 0.90 × 10⁹ CFU/g produced the most consistent improvements in growth performance, digestive function, intestinal health, antioxidant and immune responses, and gut microbial composition, and was therefore identified as the optimal supplementation level. Collectively, dietary S. laevolacticus at 0.90 × 10⁹ CFU/g improved growth performance and intestinal health in juvenile coho salmon, highlighting its potential as a probiotic candidate for coho salmon aquaculture.