Evaluating the Effects of Chlorella sp. and Schizochytrium sp. Extracts, Individually and in Combination, on Growth Performance, Body Composition, and Gene Expression Related to Growth, Digestion, Antioxidant, and Immune Responses in Rainbow Trout

Aquaculture is a fast-growing industry requires nutritionally well-balanced and sustainable feed alternatives. Microalgae such as Chlorella sp . and Schizochytrium sp. have attracted attention for their potential usability in fish culture due to their growth-promoting and immune-stimulating properties. This study aimed to assess the impact of these microalgae extracts on the growth performance, feed utilization, body composition and gene expression related to growth, digestion, antioxidant, and immune responses in rainbow trout ( Oncorhynchus mykiss ). Rainbow trout, each weighing an average of 8.92±0.04 g, were randomly allocated into 12 fiberglass tanks, with 15 fish per tank. The study comprised four treatments, including a control group (K) and experimental groups fed with 0.5% Chlorella (CH), 0.5% Schizochytrium (SC), and a combination of 0.25% Chlorella + 0.25% Schizochytrium (CH+SC) for 60 days. The results indicated that individual inclusion of Chlorella and Schizochytrium extracts up to 0.5% in the diet did not significantly affect growth performance and feed utilization. However, the combination of both microalgal extracts at the 0.5% level demonstrated significant improvements in all parameters. Notably, the expression level of the growth hormone (GH-I) gene was higher in the CH+SC and SC groups compared to the control group, indicating a potential impact on growth-related mechanisms. Regarding body composition, there were no significant differences in moisture, lipid, and ash among groups. However, fish fed the mixed treatment-supported diet exhibited high crude protein. Additionally, the expression of genes inducing digestive enzymes significantly increased in fish fed the mixed diet, suggesting enhanced digestive activity. Furthermore, the study revealed significant increases in the expression levels of antioxidant-related genes (SOD, CAT, GPx) in all experimental groups compared to the control group, indicating an improvement in antioxidant status. Immunological assessments demonstrated significant differences in the expression of immune-related genes among treatments. Adding algal extracts to the diet positively affected the expression of immune-related genes, such as LYZII, TNF-α, and IL-1β, suggesting enhanced immune responses. This work demonstrated a mixed diet containing Chlorella and Schizochytrium extracts positively influenced the growth performance of rainbow trout while enhancing digestive activity, immune responses, and antioxidant status. These findings support a combination of 0.25% Chlorella and 0.25% Schizochytrium in supplementary feed for rainbow trout in aquaculture practices. This research contributes valuable insights toward developing optimized aquafeeds for the aquaculture industry.