Effect of replacing fishmeal with stickwater hydrolysate on the growth, serum biochemical indexes, immune indexes, intestinal histology and microbiota of rice field eel (monopterus albus)

An eight-week feeding experiment was conducted to evaluate the effects of replacing fish meal with stickwater hydrolysate (SWH) on the growth, serum biochemical, immune indexes, intestinal health of Monopterus albus. The control diet was produced using fish meal (FM), and the other three diets replaced the fish meal with 5.0% (SWH5.0), 10.0% (SWH10.0), and 15.0% (SWH15.0) SWH. The results showed that the weight gain rate (WGR) of the SWH10.0 and SWH15.0 groups was significantly higher than that of the FM group, while the opposite result was found for feed conversion ratio (FCR). The activities of trypsin and amylase were significantly higher in the SWH10.0 groups than in the FM group. There were no significant differences in serum triglyceride (TG), complement 3 (C3) and malondialdehyde (MDA) contents and lysozyme (LZM), alkaline phosphatase (AKP) and superoxide dismutase (SOD) activities among all treatment groups. With increasing SWH replacement, the glucose (GLU) and alanine aminotransferase (ALT) contents were increased, and the SWH10.0 and SWH15.0 groups had a significant increase compared with the FM group. The serum aspartate aminotransferase (AST), immunoglobulin M (IgM) and C4 contents were significantly higher in the SWH10.0 group than that in the FM group. The villi length, goblet cell quantity and muscle thickness were significantly higher in the SWH10.0 groups than in the FM group. Furthermore, we observed that SWH replacement can decrease the richness and diversity of the intestinal microbiota. The dominant phylum and genus in the intestine of M. albus were Firmicutes and Clostridium, respectively. The partial replacement of fish meal with SWH increased the richness of Firmicutes and decreased the richness of Edwardsiella, which promoted the growth and immune performance of M. albus. Therefore, it could be inferred that the partial replacement of fish meal with SWH can improve the growth performance, immune function and intestinal health of M. albus. The optimal replacement ratio is 10%.