Protective effect of Nannochloropsis Oculata against mercuric-induced histopathological alterations in the kidney of Nile tilapia

Objective: The present study was designed to evaluate the toxic effect of sublethal concentration of mercuric chloride (0.3 mg/L HgCl2) on histopathological lesions in the kidney of Nile tilapia (O. niloticus) and the protective effect of microalgae, Nannochloropsis oculata (N. oculata) against the induced tissue alterations for 3 weeks. Design: Randomized controlled study Animals: Nile tilapia Procedures: Fish were randomly assigned to 4 groups, group1: control (basal diet), group 2 (Hg/ exposed to HgCl2 at a dose of 0.3 mg/L (1/4 of LC50), and fed basal diet), group 3: (Hg+N5, similar to group2, but fed diet supplemented with N. oculata 5% and group 4 (Hg+N10, similar to group2, but fed diet supplemented with N. oculata 10 %. Two fish from each aquarium tank (6 fish/group) were sampled at weeks 1, 2, and 3 of the experiment. The posterior kidney was dried out in a graded ethanol series and then embedded in paraffin. Each block of tissue was cut into serial sections (5 μm thick) and stained with hematoxylin and eosin (H&E). Results: Histopathological alterations were induced following mercuric exposure in a time-dependent manner. The kidney showed congestion, hemosiderosis, and hemorrhage with vacuolated tubular epithelium, hyaline droplet degeneration, and necrosis of the tubular epithelium. Supplementation with N. oculata, particularly at 10 %, succeeded in alleviating the histopathological induced lesions in the kidney. Conclusion and clinical relevance: Our findings demonstrate that HgCl2 has nephrotoxic properties that led to severe histopathological alterations in the kidney of Nile tilapia, while dietary supplementation with N. oculata was able to alleviate the induced kidney alterations.