Dietary oregano essential oil improved the growth performance via enhancing the intestinal morphometry and hepato-renal functions of common carp (Cyprinus carpio L.) fingerlings

The current work was designed to assess the influences of dietary oregano essential oil (OEO) on the indices of growth and feed utilization, proximate composition, hepato-renal functions, and histomorphological criteria of livers, kidneys, and intestines of common carp (Cyprinus carpio L.) fingerlings. Fish (20.3 +/- 0.8 g) were randomly divided into five treatments and fed on different levels of OEO at 0, 5, 10, 15, and 20 g/kg diet for 2 months. The results showed that the dietary OEO significantly improved the growth parameters (final body weight, weight gain, weight gain %, specific growth rate, and feed intake) (P < .05) in a dose-dependent regime; meanwhile, the feed conversion ratio was not affected with respect to the control group. The body proximate composition and survival rates were not significantly affected. The serum protein profile (total protein, albumin, and globulin), activities of liver function enzymes (alanine transaminase aspartate transaminase, and alkaline phosphatase), and renal markers (creatinine and urea) were not significantly altered (P < .05) by OEO supplementation. The histomorphology of hepatopancreatic and renal tissues of common carp fed OEO at varying levels were correlated with the serum hepato-renal functions without any noticed pathologic lesions. Moreover, the intestinal villi with associated goblet cells and crypt, tunica muscularis (both internal and external muscular layers) and submucosal tissues appeared free of inflammatory and/or degenerative changes. All intestinal morphometric measurements revealed a significant improvement (P < .05) in OEO-fed fish in comparison with the control one. Conclusively, in common carp, the dietary OEO improved growth performance and intestinal histomorphology with no inflammatory signs, and with potential hepato-protective effects with the optimum level of 15 g/kg diet. These beneficial effects were possibly because of OEO-mediated beneficial improvements in the histomorphometric criteria of the fish intestines.