An 8-week feeding trial was conducted to determine dietary lysine requirement of juvenile Pseudobagrus ussuriensis (initial body weight: 0.60 g). Six isonitrogenous (crude protein, 400 g/kg) and isolipidic (crude lipid, 50 g/kg) diets were formulated to contain graded levels of dietary lysine (12.8, 19.9, 26.5, 34.0, 40.8 and 44.1 g/kg dry diets, respectively). The results indicated that weight gain, specific growth rate, productive protein value and protein efficiency ratio increased, while feed conversion ratio decreased with increasing dietary lysine level up to 34.0 g/kg dry diet and then levelled off. Fish fed diet with 12.8 g/kg lysine had the lowest lysine content (58.6 g/kg dry matter) in muscle, while fish fed diet with 34.0 g/kg lysine had the highest value (61.6 g/kg dry matter; p < .05). Broken-line analysis on the basis of weight gain showed that the optimal dietary lysine requirement for maximum growth of juvenile Pseudobagras ussuriensis is 33.5 g/kg dry diet (82.4 g/kg dietary protein). Quadratic regression analysis of protein efficiency ratio against dietary lysine levels indicated that the optimal dietary lysine requirement of juvenile Pseudobagras ussuriensis is 36.4 g/kg dry diet (89.5 g/kg dietary protein).

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 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). Simultaneously, hepatic toll-like receptor 2 (TLR2), myeloid differentiation factor 88 (MyD88) and nuclear transcription factor kappa B p65 (NF-κB p65) mRNA levels of fish in Gos group were also up-regulated. However, dietary yeast culture supplementation remarkably prevented the increase of IL-1β and IL-8 mRNA levels and the decrease of IL-10 mRNA level by inhibiting the excessive activation of TLR2-MyD88-NF-κB signaling pathway through down-regulating TLR2, NF-κB p65 (P < .05) and MyD88 (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 < .05). Higher occurrences of the dilatation in sinusoids, karyolysis, hydropic degenerations and nuclei shifting to the cellular periphery were detected in Gos group compared with those in the control group, coupled with increased serum aspartate aminotransferase activity. Lower occurrences of these histopathological symptoms were observed in the Gos/YC group compared with those of fish in the Gos group. Overall, the results mentioned above indicated that gossypol could result in immune and oxidative damage, liver injury and inflammatory response and dietary yeast culture supplementation could alleviate these negative responses for Ussuri catfish.

An 8-week feeding trial was implemented to evaluate the effects of replacing fish meal (FM) with mussel (Cristaria plicata) meat (MM) on growth, digestive ability, antioxidant capacity and hepatic insulin-like growth factor I (IGF-I) gene expression of juvenile Ussuri catfish (Pseudobagrus ussuriensis). Three isonitrogenous and isolipidic diets were formulated to include 0, 177.5 and 355.1 g/kg of MM, accordingly, replacing 0% (M-0, control), 50% (M-1) and 100% (M-2) of FM protein, respectively. The results showed that the final body weight, weight gain, specific growth rate and feed intake were gradually decreased with dietary MM protein levels increased, but there were no significant difference between M-0 and M-1 groups (p > 0.05). The protein efficiency ratio was increased significantly with dietary MM inclusion (p < 0.05). The apparent digestibility coefficient of dry matter, crude lipid and gross energy gradually increased with increasing dietary MM protein levels, but the apparent digestibility coefficient of crude protein was not significantly affected by MM protein supplementation (p > 0.05). Fish fed diet, M-0 and M-1 remained unaffected significantly on activities of alpha-amylase and pepsin (p > 0.05), but fish fed diet M-2 had the highest activities of alpha-amylase and pepsin. Fish fed diet M-1 or M-2 had significantly lower hepatic total antioxidant capacity, superoxide dismutase and the higher malondialdehyde level compared to fish fed diet M-0. In addition, no significant difference was observed in hepatic IGF-I gene expression level for fish fed diet M-0 and diet M-1, and fish fed diet M-2 showed significantly lower hepatic IGF-I gene expression level. Therefore, we can conclude that MM protein can successfully substitute 50% of FM protein without significantly negative effect on growth, nutrient utilization, and hepatic IGF-I gene expression for juvenile Ussuri catfish, but the antioxidant capacity was negatively affected in the present study, what is more, the total replacement of FM by MM in diet may result in the inhibition of the growth and antioxidant capacity of fish.

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). Simultaneously, serum lysozyme (LZM) activity, respiratory burst activity (RBA) of phagocytes, plasma alkaline phosphatase (AKP) activity and immunoglobulin M (IgM) content were significantly improved in fish fed Y1 diet (P < 0.05). Fish fed Y1 diet had significantly higher serum alternative complement pathway activity (ACH50) and plasma complement 3 (C3) content than the Y3 group (P < 0.05). However, no significant differences were observed in plasma acid phosphatase (ACP) activity and complement 4 (C4) content among the groups (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), and the lowest CMR was observed in the Y1 group after challenge by A. hydrophila. The highest hepatic superoxide dismutase and glutathione peroxidase activities, total antioxidant capacity and the lowest malondialdehyde content were found in Y1 group, but no significant difference was found in hepatic catalase activity among the 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.