Growth Performance and Histomorphology of Intestine, Skin, Gills and Liver of Juvenile IColossoma macropomum/I Fed Diets Containing Different Levels of the Essential Oil of INectandra grandiflora/I

The present study evaluated different levels of the essential oil of Nectandra grandiflora (EONG) in the diet of juvenile Colossoma macropomum. The juveniles (0.75 ± 0.05 g) were fed four experimental diets with differing levels of EONG (0, 0.5, 0.75, and 1.50 mL/kg). After 20 days, the weight, daily weight gain, specific growth rate, and daily feed consumption per fish were highest for the fish fed 0.5 mL EONG/kg, while after 30 days, only the weight and daily feed consumption per fish for that diet remained highest. The viscerosomatic index was highest for the fish fed 0.5 mL EONG/kg while the hepatosomatic index was higher for the groups that received dietary EONG for 30 days. The juveniles fed 1.5 mL EONG/kg showed a proliferative response of the mucous cells in the gills, but the proliferation of these lysozyme- and immunoglobulin-secreting mucosal cells was higher for the skin of the fish of all EONG levels, compared to that of the control fish. The fish fed 0.5 mL EONG/kg had the greatest height and width of intestinal villi. The two highest levels of dietary EONG supplementation (0.75 and 1.50 mL/kg) reduced the hepatocyte dimensions but did not modify the centrolobular vein area. Dietary supplementation with 0.5 mL EONG/kg improved the growth, gut health, and immune response of juvenile C. macropomum.