Dietary lipid concentrations influence growth, body composition, morphology of the liver and mid-intestine, and antioxidant status of marbled eel (Anguilla marmorata)

An 8-week feeding trial was conducted to explore the effect of dietary lipid concentrations on growth, body composition, morphology of liver, and mid-intestine and antioxidant status in marbled eel (Anguilla marmorata). Fish (initial average weight 6.86 +/- 0.11 g) were held in 18 tanks (inside diameter 80 cm, height 60 cm, volume 300 L, 25 fish/tank), with triplicate treatment groups being fed to apparent satiation twice each day on isonitrogenous (421 g/kg crude protein) diets containing different concentrations of lipid (41.2, 73.9, 113.9, 146.2, 178.1, and 216.7 g/kg). The sampling procedure was implemented after 24 h of fasting. Fish fed the diets with 178.1 and 216.7 g lipid/kg grew better than fish fed the other diets. The lowest feed intake and the highest feed conversion rate were found in 41.2 g/kg group. Muscle lipid concentrations and heights of intestinal folds, enterocytes, and microvilli in mid-intestine increased as dietary lipid concentrations increased from 41.2 to 178.1 g/kg. Hepatocyte hypertrophy and lipid vacuolization were seen in liver of the fish fed 216.7 g/kg diet. Based on broken-line analysis of serum total antioxidant capacity and quadratic regression analysis of serum glutathione peroxidase and catalase, it was concluded that dietary lipid concentrations of 125.5-159.2 g/kg promoted antioxidant status. A broken-line analysis of data for specific growth rate and weight gain gave an estimated optimal dietary lipid concentration of 195.3-198.7 g/kg. Marbled eel had quite a high demand for dietary lipid to support good growth, but excessive lipid level (216.7 g/kg) may have an adverse impact on liver structure. Moreover, marbled eel may not tolerate high concentration of dietary carbohydrate.