Effect of pollution on molecular and histological bio makers in Nile Tilapia(Oreochromis niloticus)

Abstract

The increasing distribution of pollutants in the aquatic environment have been observed to be causing an integrative effect on fish. Aquatic environment contaminated by industrial effluents, agricultural discharges, and urban sewage present as common characteristic the release of xenobiotic complex mixture that potentially affect important aspect related to physiological processes in fish. Among the many biomarkers determining the effect of pollution on the fish is the alteration in molecular and organs histopathology. In the present work, fish specimen Nile Tilapia (Oreochromis niloticus), were used to evaluate the anthropogenic impact in Daberam reservoir, Daura,  in Katsina State, Northern Nigeria. Fish were caught with the help of artisanal fishermen using fleet of gillnets and cast nets of different mesh sizes. Tissues (Gills, liver, kidney, intestine, spleen, and muscles) were dissected from the fish, preserved for histology, sectioned, and stained in hematoxylin and eosin. The sections were observed under a light microscope. Also, gene expression profiling was used to assess the impact of contamination on tilapia in the polluted aquatic site. RNA extraction and cDNA synthesis were used to measure tilapia hepatic expression using QPCR. Some of the histopathological lesions observed in gills included lamella fusion, damage of secondary lamella and necrosis. While in the liver, necrosis and vacuolation were apparently observed. Kidney lesions showed dilation of glomerulus capillaries and dilations of bowman’s spaces. In the spleen, there were presence of melanomicrophages and necrosis. In the intestine, contraction of submucosal tissue was observed while in the muscle, there were vacuolation and necrosis. Significant changes in the expression levels of genes predicted to be involved in different physiological and metabolic signalling pathways were observed in the polluted sites compared to reference site. According to the result, individual from thepolluted studied site presented exposure to different stressors indicating various molecular, cellular, and histological alterations in response to chemical contaminants presents in the aquatic sites within the vicinity of the fish. This highlights the importance of molecular and histopathological investigation in biomonitoring program to assess the water quality and the impact of xenobiotic causing effect to the wild biota especially fish.

RNA, Histopathology, Oreochromis niloticus, Daberam, QPCR, Biomakers