Effects of dietary supplements Sargassum ilicifolium and Spirulina platensis on growth parameters, immunity and gene expression in juvenile Asian seabass (Lates calcarifer)

Background: Microalgae and macroalgae play significant roles in aquaculture, offering various benefits that contribute to sustainable practices in the industry. Methods: The aim of this research was to investigate the impact of feeding Lates calcarifer a combination of Sargassum ilicifolium and Spirulina platensis on growth, immune responses, and the expression of TNF-alpha, IL-1 beta, and IGF-1 genes. Six hundred juvenile Asian sea bass, weighing about 50 +/- 2 g, were divided into five groups: a control group (CTRL) and groups receiving varying percentages of Sargassum ilicifolium and Spirulina platensis (1.5 %, 2%, 2.5%, and 3%). Results: The results showed that adding 2.5 % combined algal supplement (CAS) to the diet of Asian seabass increased the activity of digestive enzymes such as lipase, trypsin, and alpha-amylase in the gastrointestinal tract. Also, a significant increase (P < 0.05) in weight gain (WG) and specific growth rate (SGR) and a significant decrease in the feed conversion ratio (FCR) were noticed in CAS-fed fish. The highest levels of skin mucus lysozyme activity and total Ig levels were observed in the group that received 2.5 % CAS (P < 0.05). Furthermore, this group also showed the highest levels of complement C3, respiratory burst activity, and total Ig in the serum (P < 0.05). At the molecular level, using 2.5 % dietary CAS was associated with a significant increase in the expression of TNF-alpha, IL-1 beta, and IGF-1 genes compared to the control group (P < 0.05). The study also demonstrated that feeding Asian seabass with 2.5 % CAS resulted in a significant increase in the survival rate of juvenile fish exposed to Vibrio harveyi. Conclusions: These results showed that using combined S. ilicifolium and S. platensis can be considered a beneficial feed additive for Asian seabass aquaculture.