Enhancement effects of microalgae against heavy metals-induced toxicity in Oreochromis niloticus fish with emphasis on hematological, immunological and histological aspects

Abstract

Microalgae can be used as natural feed supplements for fish protection against heavy metal toxicity. The present study investigated the effect of a mixture of heavy metals (Zn, Cu, & Pb) on Oreochromis niloticus and the potential protective roles of the microalgae ―Chlorella vulgaris and Spirulina platensis‖ against heavy metals toxicity for 35 days. Upon the addition of 10 & 15% of C. vulgaris and S. platensis in fish diets, an improvement was detected in the hematological parameters (RBCs, WBCs, Hb, Ht, MCV, MCH, & MCHC) of fish exposed to heavy metals. Meanwhile, several histopathological alterations were observed in the gills, liver, intestine and muscles of fish as a result of heavy metals accumulation in these orgains. However, a decrease was recorded in the histopathological changes regarding the examined tissues of heavy metals-treated fish upon using C. vulgaris and S. platensis. In addition, C. vulgaris and S. platensis showed a marked reduction in the bioaccumulation of Zn, Cu, & Pb in the liver, intestine and muscles. Besides, C. vulgaris and S. platensis decreased the immunohistochemical expression of the proinflammatory cytokine ―tumor necrosis factor alpha (TNF-α)‖ and increased the expression of the proliferative protein (ki-67) in the examined tissues of the exposed fish. It was deduced that, C. vulgaris and S. platensis in fish diets provided protection against heavy metals inducing hematotoxicity, immunotoxicity and hisopathological alterations of O. niloticus fish.