THE OPTIMAL SUPPLEMENTATION LEVELS OF MICRO-MINERALS IN THE DIET OF JUVENILE AMERICAN EEL (<italic>ANGUILLA ROSTRATA</italic>) BASED ON INTESTINAL HEALTH

This trial aimed to determine the optimal supplementation level of inorganic micro-minerals (IMM) in the diet of juvenile American eel (<italic>Anguilla rostrata</italic>) by evaluating the intestinal health related indicators. A total of 500 fish with an average body weight of (22.99±0.15) g were randomly divided into five treatment groups, they were fed a basal diet supplemented with 0, 600, 1200, 1800, and 2400 mg/kg of a compound IMM premix, respectively. In each group, there were four replicates with 25 fish per replicate, and the trial lasted for 70d. The compound IMM premix contained Cu 10.0 g, Fe 150 g, Mn 33 g, Zn 83 g, I 4.17 g, Se 0.67 g, and Co 0.67 g. With the increasing supplementation levels of compound IMM premix, activities of intestinal amylase, lipase, protease, total superoxide dismutase, catalase and glutathione peroxidase, intestinal villi height, the muscularis propria thickness, and the microvilli density initially increased and then decreased, with the highest values observed in the 1200 mg/kg premix group. Conversely, serum D-lactic acid levels, diamine oxidase activity, and intestinal malondialdehyde levels showed an initial decrease followed by an increase, with the lowest values in the 1200 mg/kg group. The supplementation of 1200 mg/kg compound IMM premix in the diet could beneficially regulate intestinal flora composition by increasing the relative abundance of beneficial bacteria and inhibiting potentially pathogenic bacteria. By using the serum D-lactic acid level, diamine oxidase activity, and intestinal villus height as the evaluation indices, quadratic regression model was employed to estimate the appropriate supplementation levels of the compound IMM premix as 900, 1150, and 916 mg/kg, respectively. Considering the overall effects on improving intestinal health in juvenile American eels, the appropriate supplementation level range of the compound IMM premix was 900—1200 mg/kg, which provide dietary concentrations of Cu 9.0—12.0 mg/kg, Fe 135—180 mg/kg, Mn 30—40 mg/kg, Zn 75—100 mg/kg, I 3.75—5.00 mg/kg, Se 0.60—0.80 mg/kg, and Co 0.60—0.80 mg/kg. These results might provide a reference for studying trace mineral requirements and formulating scientific diets of eels.