Vol.:(0123456789) 1 3 Fisheries Science https://doi.org/10.1007/s12562-018-1274-6 ORIGINAL ARTICLE 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 Eman Zahran 1  · Walaa Awadin 2  · Engy Risha 3  · Asmaa A. Khaled 4  · Tiehui Wang 5 Received: 25 June 2018 / Accepted: 21 October 2018 © Japanese Society of Fisheries Science 2018 Abstract 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 fsh fed with a control diet or diets containing Chlorella vulgaris (Ch) after exposure to sodium arsenite (NaAsO 2 ) in Nile tilapia (Oreochromis niloticus) with the aim of evaluating the protective role of Ch against arsenite-induced toxicity. Severe histo- pathological alterations were evident in fsh exposed to 7 ppm (parts per million) arsenite for 21 days, compared to unexposed fsh. 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 signifcantly upregulated after arsenite exposure. However, in fsh 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 efects. These results suggest the protective and therapeutic roles of Ch as a feed supplement in Nile tilapia against arsenic induced toxicity. Keywords Fish · Heavy metals · Algae · Immunity · Enzymatic activity · Tissue alterations Introduction The contamination of aquatic ecosystems is one of the major threats worldwide afecting aquatic lives. Heavy metal pol- lution is one of these threats (Ahmed et al. 2013), where the exposure of heavy metals in living organisms leads to various deleterious health hazards such as immunotoxicity, genotoxicity, and nephrotoxicity (Cobbina et al. 2015). Arse- nic (As) is one of the most hazardous heavy metals that is released in the aquatic environment through both geogenic and anthropogenic processes (ATSDR 2002). In aquatic habitats, As is biologically available to organisms, including fsh, by the aid of several species of microorganisms (Duker et al. 2005; Gonzalez et al. 2006). Fish, in particular, are very sensitive to these pollutants in their environment, and are considered a good model for monitoring potential risks associated with them (Lakra and Nagpure 2009). Arsenite (As 3+ ) and arsenate (As 5+ ) are the predominant types present Aquaculture * Eman Zahran emanzahran@mans.edu.eg 1 Department of Internal Medicine, Infectious and Fish Diseases, Faculty of Veterinary Medicine, Mansoura University, Mansoura 35516, Egypt 2 Department of Pathology, Faculty of Veterinary Medicine, Mansoura University, Mansoura 35516, Egypt 3 Department of Clinical Pathology, Faculty of Veterinary Medicine, Mansoura University, Mansoura 35516,  Egypt 4 Animal and Fish Production Department, Faculty of Agriculture Saba Basha, Alexandria University, Alexandria, Egypt 5 Scottish Fish Immunology Research Centre, School of Biological Sciences, University of Aberdeen, Aberdeen AB24 2TZ, UK