<i>Enterococcus faecium</i> Supplementation: Impacts on Growth and Health of Pikeperch ( <i>Sander lucioperca</i> )

Abstract Sustainable development of aquaculture requires exploring strategies to enhance fish growth and welfare. This study assessed the pro-biotic potential of Enterococcus faecium on growth, immunity, and gut microbiota of farmed Sander lucioperca (Gilan, Iran). For this purpose, 180 fish (14.5±0.5 g) were distributed into 12 tanks and fed 4% of their biomass with four experimental diets, including a basal diet (C), basal diet with kanamycin aesculin azide (CP), and basal diets supplemented with 10 10 (EF1) and 10 8 (EF2) CFU/g E. faecium for 60 days. Results showed significantly higher weight gain and specific growth rate values in fish from EF1 and EF2 groups compared to other treatments (P&lt;0.05). In addition, the feed conversion ratio in EF1 (0.89±0.05) and EF2 (0.83±0.07) was significantly lower than the control group (1.56±0.05), indicating higher feed utilization efficiency in probiotic-fed fish (P&lt;0.05). Regarding serum biochemical parameters, no significant changes were observed for cholesterol, triglyceride, and albumin levels, while total protein and glucose levels were highest in EF1 and EF2 treatments (P&lt;0.05). Fish from EF1 and EF2 exhibited significantly higher lysozyme activity, IgM level, and complement activity (C3 and C4) compared to other treatments (P&lt;0.05). In addition, significantly lower ALP (alkaline phosphatase), ALT (alanine transaminase), and AST (aspartate aminotransferase) activities were observed in EF2 treatments. Finally, the total number of lactic acid bacteria (LAB) in the intestinal tract of fish from the EF1 and EF2 groups was greater than that in the other groups. Along with a significant increase in the total bacterial count and LAB in the gut, it is concluded that E. faecium at 10 10 CFU/g diet can improve the growth performance and immune parameters of S. lucioperca .