Effects of composite lactic acid bacteria on the growth, intestinal physiology, and non-specific immunity of sea cucumber (Apostichopus japonicus)

To investigate the effects of composite lactic acid bacteria (LAB) on the growth performance, intestinal physiology, and non-specific immunity of sea cucumbers, experiments were conducted using sea cucumbers with an average body weight of 2.43 +/- 0.02 g. Five experimental groups were designed, with 3 replicates per group and 20 sea cucumbers per replicate. The sea cucumbers were fed with feed containing different concentrations of composite LAB (0%-Control, 0.5%, 1%, 1.5%, and 2%) for 56 days. The findings demonstrated a significant enhancement in the body weight gain (BWG) and specific growth rate (SGR) of the sea cucumber upon supplementation with the composite LAB. The activity of digestive enzymes in each experimental group was significantly higher than that in the control group. The activities of superoxide dismutase (SOD), lysozyme (LZM), catalase (CAT), total antioxidant capacity (T-AOC), acid phosphatase (ACP), alkaline phosphatase (AKP), and polyphenol oxidase (PPO) in each experimental group were all significantly higher than those in the control group. Among them, the activities of SOD, LZM, T-AOC, and AKP increased with the increase in the amount of additive, while the activities of CAT and ACP peaked when the additive amount was 1.5%. The content of malonaldehyde (MDA) showed a continuous declining trend. The incorporation of the composite LAB into the feed resulted in a significant enhancement of intestinal villus height (I-VH) and intestinal villus width (I-VW) in sea cucumbers. The experimental groups exhibited elevated expression levels of immune and growth-related genes compared to the control group. The experimental results indicate that the addition of composite lactic acid bacteria in the feed has a positive effect on the growth performance, intestinal physiology, and immune indicators of sea cucumbers, with the best results observed at an additive level of 1.5%.