Effects of dietary 1,8-cineole supplementation on growth performance, antioxidant, and immunological responses of Nile tilapia, Oreochromis niloticus, reared in different stocking densities

Abstract

This study aimed to evaluate the effects of dietary 1,8-cineole (CIN) on Nile tilapia, Oreochromis niloticus, reared at different stocking densities. Fish (average initial weight 13.2 ± 0.35 g) were fed diets supplemented with 0%, 0.25%, or 0.5% CIN and stocked at either 14 (normal) or 56 (high) fish per 120-L tank. The fish were reared for 8 weeks in triplicate and fed the diets at a rate of 4% per day. The results showed no significant interaction effects between dietary CIN and stocking density for any of the parameters tested. Also, there were no significant differences between 0.25% and 0.5% CIN treatments in any tested parameters. Dietary CIN and stocking density had no significant effects on feed efficiency and fish growth rate, plasma cortisol, and glucose levels. Dietary CIN significantly increased the plasma total antioxidant capacity and hepatic superoxide dismutase activity, but decreased hepatic malondialdehyde levels. The increase in fish stocking density significantly increased the plasma total antioxidant capacity and hepatic malondialdehyde levels. Dietary CIN and stocking density had no significant effect on the hepatic catalase activity. Dietary CIN significantly increased skin mucus alkaline phosphatase and plasma alternative complement activities, but fish stocking density had no significant effect on these parameters. Dietary CIN significantly increased lysozyme activities and immunoglobulin levels in plasma, skin mucus, liver, and kidney. The increase in fish stocking density significantly decreased lysozyme activities in plasma, skin mucus, and liver, but increased the kidney lysozyme activity. Moreover, the increase in fish stocking density significantly increased immunoglobulin levels in the liver and skin mucus, but decreased them in the plasma. In conclusion, this study demonstrates that an increase in stocking density up to 56 fish per 120-L tank had no detrimental effect on feed efficiency and growth performance of Nile tilapia. Also, dietary CIN does not affect Nile tilapia growth but boosts antioxidant and immune systems, which may improve fish welfare and resilience. Hence, dietary 0.25% CIN supplementation is recommended for Nile tilapia feed formulation.