Dietary supplementation of Chlorella vulgaris ameliorates chronic sodium arsenite toxicity in Nile tilapia Oreochromis niloticus as revealed by histopathological, biochemical and immune gene expression analysis

Arsenic toxicity in an aquatic environment is a major concern, and its elimination has become a global challenge. In the current study, histopathology, serum biomarkers and cytokine gene expression were comparatively examined in fish fed with a control diet or diets containing Chlorella vulgaris (Ch) after exposure to sodium arsenite (NaAsO2) in Nile tilapia (Oreochromis niloticus) with the aim of evaluating the protective role of Ch against arsenite-induced toxicity. Severe histopathological alterations were evident in fish exposed to 7 ppm (parts per million) arsenite for 21 days, compared to unexposed fish. Levels of serum biomarkers ALT, AST, ALP, urea and creatinine were increased, but the levels of Na+, total proteins, albumins and globulins were decreased. Moreover, the expression of all the cytokine genes examined, including IL-1β (7-fold), TNF-α (14-fold) and TGF-β1 (13-fold), were significantly upregulated after arsenite exposure. However, in fish fed with diets containing 5% or 10% Ch, the histopathological alterations in the gills, liver and head kidney were reduced, the biomarkers were stabilized, and the upregulation of cytokine gene expression was lowered, with the high Ch diet (10%) showing more prominent effects. These results suggest the protective and therapeutic roles of Ch as a feed supplement in Nile tilapia against arsenic induced toxicity.