Effects of dietary chitosan-flaxseed oil nanoemulsion on growth, economic performance, immunity, intestinal health, and cold-stress resistance in Nile tilapia (Oreochromis niloticus).

The current study aimed to assess the potential biological and cellular impacts of dietary supplementation with chitosan-flaxseed oil nanocomposite (CFN) in boosting the growth performance indices, digestive enzyme activity, innate immune capacity, economic significance, gene expression, and histopathological alterations in the Nile tilapia exposed to chronic cold stress. Nile tilapia were distributed into six experimental groups, the first three groups were reared under optimum water temperature (25 °C) and fed 0 mg/kg CFN (control), 20 mg/kg CFN or 40 mg/kg -incorporated diets, respectively. However, the other three groups were reared under cold stress conditions (18 °C), and received the same previously mentioned diets, respectively. Growth performance and economic significance analysis were monitored throughout the experiment. Serum and tissue samples were collected after 60 days to evaluate immune indices (lysozyme, nitric oxide, and IgM), glucose, growth hormone (GH), digestive enzymes (amylase and lipase), gene expression (interleukin-8, tumor necrosis factor-alpha, interleukin-1ß, lysozyme-G, lysozyme-C, transforming growth factor-beta, nuclear factor kappa β, myeloperoxidase, and Toll-like receptor-5, and glutathione perioxidase-1), and histopathological changes. A subsequent bacterial challenge with Pseudomonas aeruginosa was carried out, where the clinical disorders and mortalities were monitored. The outcomes showed remarkable declines in various growth metrics, immune variables with dysregulation in the immune-linked genes in fish exposed to chronic cold stress circumstances, compared to fish reared at optimum temperature. Nonetheless, dietary intervention with CFN mitigated the negative impacts induced by cold stress exposure, where the growth, immune indices, and digestive enzymes were notably enhanced in the supplemented groups in relation to the non-supplemented group. The histopathological alterations in the intestine and spleen were also markedly alleviated. Additionally, the expression profiles of both inflammatory cytokines and apoptosis were positively modified. Furthermore, fish resilience to P. aeruginosa infection was triggered, which was evident by the amelioration of the clinical signs and declining mortality rates in CFN-enriched groups. Taken together, CFN is a promising antibacterial dietary additive which promotes the growth, health, and performance of the Nile tilapia.