Effects of Feed Additives (Nannochloropsis gaditana and Hermetia illucens) on Growth and Expression of Antioxidant and Cytokine Genes in Nile Tilapia (Oreochromis niloticus) Subjected to Air Exposure Stress

A 7-week feeding trial was conducted with Nile tilapia juveniles with an average body weight of 143.5 ± 3.1 g in a cage system in order to test the effect of different feed additives on growth performance, antioxidant defense system, and immune status of fish. For this reason, experimental diets were formulated with inclusion of two different additives containing bioactive compounds, namely <i>Nannochlorophsis gaditana</i> in 3.5% (diet EXP-A) and black soldier fly larvae meal (diet EXP-I) in 3.5%, and compared with a diet supplemented with a mixture of two different commercial compounds (Yang and Syrena Boost) in 0.4% (diet EXP-S). As a negative control, a commercially available feed (Nongteng, Laos) for tilapia was selected. At the end of the feeding trial, production parameters and expression of genes related to the antioxidant defense system and innate immune response were studied. Furthermore, following the feeding, air exposure stress for 5 min was administered to the fish, and similar parameters were assessed. Results indicated that all diets promoted adequate fish growth (SGR 1.67-1.81 g day^-1) and feed utilization (FCR 1.29-1.57 g g^-1) with no significant (<i>p</i> < 0.05) differences in these parameters between the dietary fish groups. Expression of genes <i>sod</i>, <i>cat</i>, and <i>gpx</i> significantly increased in the liver samples of the EXP-A group at the end of feeding. Following air exposure, the EXP-A group maintained a significantly higher level of antioxidant-related gene expression compared to other treatments. Subsequently, <i>gpx</i> upregulation was observed in the EXP-S group in the post-stress stage compared to pre-stress. Based on our results, we recommend the inclusion of any of the tested additives at the evaluated doses to enhance the non-specific immune response of Nile tilapia. Additionally, <i>Nannochloropsis gaditana</i> at a 3.5% inclusion level can be used to further improve antioxidant defense capacity.