Nano-Oregano Essential Oil Improves Rainbow Trout’s (Oncorhynchus mykiss) Growth Performance, Oxidative Status, Fatty Acid Profile of Fillet, Affects Gene Expression and Supports Skin and Intestinal Histomorphometry

Abstract The present study was conducted to investigate the effects of a microencapsulated oregano feed additive containing oregano essential oil named “VISNAT 1” on growth performance, intestinal and skin histomorphometry, serum biochemical parameters, fillet oxidative status and fatty acids (FA) profile of rainbow trout ( Oncorhynchus mykiss ) under conventional farming conditions. Also, changes in the expression levels of both insulin-like growth factor-1 (IGF-1) and growth hormone 1 (GH-1) genes were assessed. A total of 200 sub-adult trouts (52 g±3.2) were randomly allocated into two different treatments with four replicates each. The control group was fed a basal diet, while oregano group was fed diet supplemented with oregano essential oil at the level of 1.0 kg/t of feed. The results indicate that the phytobiotic product beneficially altered feed, fillet and serum oxidative status and improved performance of trouts. Also, oregano essential oil beneficially affected the histopathology and histomorphometry of intestine and skin. Moreover, oregano oil addition in the rainbow trout diet can initiate mitogenic and anti-apoptotic responses in the liver, which is one of the main actions of IGF-1 receptor promoting body growth and health. As a result, oregano essential oil can be used as a supplement on trouts diet but further investigation upon its action should take place.