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This study evaluated the effects of replacing fishmeal with mussel meal or meat and bone meal in low‐FM diet on growth performance, body composition, digestibility, antioxidant capacity and IGF‐I gene expression in juvenile Ussuri catfish (Pseudobagrus ussuriensis). The results showed that no significant changes in SGR, FE and PER were observed between MM₄₀ and LFM groups, but significantly reduced result was found in MBM₄₀ group. MM₄₀ group showed the higher ADC of lipid (93.30%) and lipase activity (95.00 U/gprot) than LFM group (90.97%; 70.18 U/gprot). MM₄₀ or MBM₄₀ diets led to significant reduction of SOD and CAT activities. MM₄₀ group showed significantly higher MDA level (5.84 nmol/mg) than LFM group (4.73 nmol/mg). The activities of LZM decreased significantly in MM₄₀ and MBM₄₀ groups compared with LFM group. MM₄₀ and MBM₄₀ groups showed no significant difference in hepatic IGF‐I gene expression levels compared with LFM group. The findings demonstrated that MM could substitute 400 g/kg of FM in low‐FM diet for Ussuri catfish without influencing the growth, but to some extent, spontaneous oxidative stress and immune damage could occur; when 400 g/kg of FM was replaced by MBM, significantly negative effects were observed on growth, antioxidant capacity and non‐specific immune response of Ussuri catfish.

The aim of the present study was to investigate effects of dietary yeast culture on immune response related to TLR2-MyD88-NF-kβ signaling pathway, antioxidant capability and disease resistance against Aeromonas hydrophila for Ussuri catfish (Pseudobagrus ussuriensis). A total of 240 Ussuri catfish (mean weight of 7.39 ± 0.32 g) were randomly distributed into four groups that fed diets containing 0 (Y0), 10 (Y1), 20 (Y2) and 30 (Y3) g kg−1 yeast culture for 8 weeks. The results indicated that dietary 10 g kg−1 yeast culture supplementation significantly down-regulated mRNA levels of TLR2, MyD88, NF-kβ p65, IL-1β and IL-8 in the liver tissue compared with the control group (P 0.05). Fish cumulative mortality rate (CMR) in the Y1 and Y2 groups were significantly lower than that in Y0 and Y3 groups (P 0.05). These results demonstrate that dietary 10 g kg−1 yeast culture could effectively improve the immunity, antioxidant capability and disease resistance against A. hydrophila for Ussuri catfish and could down-regulate the mRNA expression levels of pro-inflammatory cytokines modulated by TLR2-MyD88-NF-kβ signaling pathway.

The present study explored the mechanisms of gossypol induced inflammatory response in liver tissue of Ussuri catfish (Pseudobagrus ussuriensis), and investigated whether the yeast culture could relieve the inflammatory response of fish. For this purpose, Ussuri catfish were fed two diets with or without yeast culture for 8 weeks, and then fish were treated with 300 mg gossypol/kg body weight by intragastric administration for 15 days. Fish pre-fed diet without yeast culture supplementation and treated with gossypol oral administration (Gos group) had higher interleukin-1β (IL-1β) and interleukin 8 (IL-8) mRNA levels compared with fish pre-fed diet without yeast culture supplementation and treated with sodium carboxymethylcellulose solution oral administration (control group) and pre-fed yeast culture diet and treated with gossypol oral administration (Gos/YC group), but had lower interleukin 10 mRNA level than the control group (P .05) mRNA levels. Besides, the lowest serum lysozyme and alkaline phosphatase activities were observed in fish of Gos group. There was an increased trend in immunoglobulin M content among the groups. Fish in Gos group had significantly lower hepatic catalase, superoxide dismutase and total antioxidant capacity compared with those fish in the control group (P