Natural Dietary Supplementation with Elionurus muticus Essential Oil Enhances Growth Performance and Modulates Physiological Responses to Transport Stress in Nile Tilapia

This study evaluated the effects of dietary Elionurus muticus essential oil (EMEO) on growth performance, physiological responses, and resistance to car transport stress in Nile tilapia (Oreochromis niloticus). Fish were fed experimental diets for 60 days and subsequently subjected to 6 h of transport stress. Five diets were tested: 0.00 (control), 0.25, 0.50, 1.00, and 1.50 mL EMEO kg−1, in triplicate (10 fish per 500 L tank; stocking density 0.4 kg L−1). Citral was the major EMEO compound (73.91%). Increasing dietary EMEO levels improved growth performance and reduced the feed conversion ratio. Before transport, EMEO supplementation increased erythrocyte counts and plasma glucose levels, while reducing hematocrit and hepatic aspartate aminotransferase (AST) activity (p < 0.05). After transport, plasma glucose, hematocrit, and hepatic AST values decreased, whereas hepatic glycogen and hemoglobin levels increased with higher EMEO inclusion (p < 0.05). Also, post-transport, EMEO-fed fish showed enhanced intestinal digestive enzyme activity (lipase and amylase) and antioxidant capacity (superoxide dismutase and ferric reducing antioxidant power) but increased protein carbonyl levels. Lipid peroxidation (malondialdehyde) was reduced at intermediate EMEO levels (p < 0.05). Histological analyses indicated no tissue damage and suggested improved liver and intestinal function with increasing EMEO inclusion. Overall, dietary supplementation with 1.00 mL EMEO kg−1 is recommended to enhance growth performance and metabolic adjustment and to improve physiological status to withstand transport stress in Nile tilapia.