LAUSR

Abstract An eight weeks feeding trial was conducted to assess the effects of dietary sodium butyrate (NaB) supplementation in diets with graded levels of soybean meal (SBM) on growth performance, antioxidant status, immune response, intestinal digestive enzymes activities and morphology of rice field eel Monopterus albus (initial body weight 14.87 ± 0.11 g). Using the 2 × 4 experimental design, eight isonitrogenous (42% crude protein) and isolipidic (5.5% crude lipid) experimental diets were formulated to contain two SBM levels (18% and 33%, designed as SBM18 and SBM33) and four levels of NaB (0, 250, 500, 1000 mg kg−1 dry diet). The results showed that NaB supplementation significantly increased weight gain (WG), serum superoxide dismutase (SOD) activity and significantly decreased malondialdehyde (MDA) content of fish fed diets with 33% SBM (P   .05). At each NaB level, WG of fish fed with 33% soybean meal diet was significantly lower than that of 18% soybean meal except for at 500 mg kg−1 level. Not NaB level but SBM level significantly influenced the feed intake (FI) (P