Effects of sodium butyrate on the growth performance, digestive enzyme activity, intestinal health, and immune responses of Thinlip Grey Mullet (Liza ramada) juveniles

Sodium butyrate (SB) is an active organic acid usually applied in aquaculture. Hence, the effects of SB were investigated on the growth performance, digestive enzyme activity, and blood biochemistry of Thinlip Grey Mullet (Liza ramada) in this study. Five test diets with an average protein level of 30.33 % and energy of 18.22 MJ/kg were formulated to include SB supplementation at 0, 0.5, 1, 2, and 4 g/kg. In 15 enclosures (0.5 ×0.5 ×1 m), 225 fish were divided equally, where each hapa was stocked with 15 fish with an average weight of 7.79 ± 0.04 g/fish. Every three hapas represented one experimental group (triplicates). Fish were kept under average water temperature (25.12 ± 0.33 °C), salinity (11.46 ppt), and total ammonia (0.16 ± 0.01 mg/L) during the trial. The enclosures were fixed in a concrete tank with running water in a flow-through system, and fish were fed the control diet at 3 % of the body weight twice daily (08:00 and 15:00) for 60 days. At the end of the trial, all fish were fasted for 24 h, weighed and counted, then blood samples collected, and intestines and livers were dissected. The results revealed that fish-fed SB had higher growth performance, feed intake, protein efficiency ratio, and protein productive value than fish-fed SB-free diet (P < 0.05). On the other hand, the feed conversion ratio was reduced by dietary SB in a dose-dependent manner (P < 0.05). The lipase activity was increased in fish fed SB at 1 and 2 g/kg, while the amylase activity of fish fed 0.5, 1, and 2 g/kg (quadratic P < 0.05). Markedly, the protease activity in fish fed SB was higher than those fed SB free diet regardless of the inclusion rate (P < 0.05). The histopathological assessment of fish-fed SB showed that all layers of intestinal villi and the intestinal wall appeared intact, without any abnormal changes. The intestinal mucosa of groups supplemented with SB exposed improved, branched, and well-arranged intestinal villi. The total serum protein, albumin, and globulin were significantly increased in fish-fed SB at 1, 2, and 4 g/kg (quadratic P < 0.05). The lysozyme and phagocytic activities were increased quadratically in mullets fed dietary SB at 1, 2, and 4 g/kg (P < 0.05). The regression analysis revealed that dietary SB is required at 2.19–2.54 g/kg to enhance the growth performance, digestion, and well-being of mullets.