A high-fat diet alters lipid accumulation and oxidative stress and reduces the disease resistance of overwintering hybrid yellow catfish (Pelteobagrus fulvidraco♀×P. vachelli♂)

This study was carried out to investigate the influence of dietary lipid levels on the growth, immune response, and disease resistance of hybrid yellow catfish (Pelteobagrus fulvidraco♀×P. vachelli♂) during overwintering. Yellow catfish (initial body weight: 49.42 ± 1.33 g) were fed isonitrogenous diets (crude protein 40%) with three lipid levels (low lipid: 8.57%, medium lipid: 12.65%, and high lipid: 16.60%) for five weeks before the overwintering stage, and then all fish were fasted during overwintering. After overwintering, a bacterial challenge test was performed. The results showed that dietary lipid levels had no influence on the growth of hybrid yellow catfish before or after overwintering, but the high lipid (16.60%) diet significantly reduced the survival rate of the fish after bacterial challenge (P < 0.05). Crude whole-body fat content in each treatment after overwintering was significantly lower than that before overwintering. In addition, the liver lipid content significantly increased with increasing dietary lipid levels (P < 0.05). Before overwintering, expression levels of genes related to lipogenesis and lipolysis pathways in liver tissue were down-regulated by the 16.6% lipid diet (P < 0.05). Plasma superoxide dismutase (SOD) activities and malondialdehyde (MDA) contents were enhanced with the increase of dietary lipid level before the challenge test. Plasma SOD activities and MDA contents were significantly decreased in the high lipid group, and plasma cortisol content and lysozyme (LYZ) activity in the 16.60% lipid group were significantly higher than those in the 8.57% lipid group (P < 0.05) at 12-h post bacterial challenge. The mRNA expression levels of toll-like receptor 2 (tlr2) in spleen post-challenge were significantly downregulated compared to pre-challenge (P < 0.05). The transcriptional levels of interleukin 1β (il-1β), tumor necrosis factor α1 (tnfα1), interleukin 10 (il-10), and immunoglobulin M (igm) in spleen or kidney were significantly increased post-challenge compared to pre-challenge, and the relative expression levels of immune-related genes in the high lipid group were greater than those of the low lipid group post-challenge (P < 0.05). The results indicated that high dietary lipid (16.60%) induces oxidative stress and reduces disease resistance of hybrid yellow catfish through a pathway involving regulation of tlr and the inflammatory response during overwintering.