Abstract
Climatic change is a grave and growing threat to natural systems and aquatic species. Cold stress has caused a great worldwide economic loss in aquacultures worldwide. This study aimed to evaluate the effect of dietary Spirulina (Arthrospira platensis) on immunobiochemical parameters, antioxidants, some metabolic gene expressions, and histological structure of liver and kidney of Nile tilapia (Oreochromis niloticus) under cold stress. One hundred and sixty Nile tilapia were divided into eight groups (10 fish per aquarium) in two replicates. The first four groups were maintained at 26 °C whereas, the rest were subjected to 17 °C cold stress. They were fed three spirulina-contained diets (0.75, 1.5, and 3%) and a control diet for three weeks. Blood and tissue samples were collected from all groups after exposure to cold stress. The results of the cold-stressed group that fed control diet showed a significant decreases in the serum level of cortisol, catalase, superoxide dismutase, phagocytic activity, tumor necrotic factor α, Interleukin 1β, Interleukin 6, and Interleukin 17. Also, it explored a significant increased serum level of heat shock protein 70, glucose, Interleukin 10, and malondialdehyde, beside up-regulation of Phosphoenolpyruvate carboxykinase 1, and mitochondrial transcription factor A genes. In addition to, alteration of liver and kidney biomarkers with severe histopathological perturbations of liver and kidney were detected. Dietary Spirulina supplementation at 0.75% during cold stress ameliorate the immune and antioxidant status, biochemical parameters and protecting the integrated tissue architecture from oxidative damage of Nile tilapia.

Key words: Nile Tilapia; Spirulina Platensis; Cold stress; Interleukin 17.