An evaluation of replacing fish meal with cottonseed meal in the diet of juvenile Ussuri catfish Pseudobagrus ussuriensis: Growth, antioxidant capacity, nonspecific immunity and resistance to Aeromonas hydrophila

An 8-week feeding trial was conducted to evaluate the effects of replacing fish meal (FM) with cottonseed meal (CM) on growth and immune characteristics of juvenile Ussuri catfish Pseudobagrus ussuriensis. Seven isonitrogenous and isolipidic diets were formulated to contain CM to replace fish meal at 0 (C0, control), 10 (C10), 20 (C20), 30 (C30), 40 (C40), 50 (C50) and 60% (C60), respectively. The replacement level up to 30% did not affect the weight gain and specific growth rate, whereas these parameters were depressed by further replacement level. The apparent digestibility coefficient of dry matter, crude protein and crude lipid decreased with increasing dietary CM level. Fish fed C60 diet had the lowest hepatic total antioxidant capacity but the highest malondialdehyde level. The activities of serum lysozyme, plasma myeloperoxidase and plasma alkaline phosphatase decreased as the proportion of CM increased. Conversely, the inclusion of CM increased the plasma alanine aminotransferase, aspartate aminotransferase and lactate dehydrogenase activities. The highest heat shock protein 70 gene expression level was observed in fish fed the C60 diet. In addition, percent mortality increased after challenge with Aeromonas hydrophila. Percent mortality of fish fed the C60 diet was significantly higher than the other groups. Broken-line model analysis based on WG against dietary CM replacement level indicated that the optimum replacement level was 25.3%. However, including too high proportion of CM could depress the antioxidant capacity, non-specific immune response and resistance to A. hydrophila infection of Ussuri catfish.