The histological alterations in gills and liver of <i>Tilapia guineensis</i> exposed to common drilling fluids in the delta of river Niger

Abstract

This study investigated the histological changes on gill and liver of fry, fingerling and post-fingerlings of Tilapia guineensis exposed to sublethal concentrations of drilling fluid for 12 weeks. The concentrations used were 0.32%, 0.63%, 1.25% and 2.5% vol/vol (Note 1% = 1000ml/L). The results revealed that little or no lesions were observed in the gills and liver with the exception of those exposed to the highest concentration. The gill filaments of the fish exposed to the highest concentration of the toxicants (2.5%) had mild lesion which was characterized by epithelial lifting and hyperplasia of the gill lamellae, while the liver exhibited mild vacuolations, presence of macrophages and slight sloughing of the cell. Although toxic responses had been identified in the tissues of fish exposed to acute concentrations of drilling fluids, the subtle changes identified in the tissues of the exposed fish divulge regenerative response in terms of functions and histology. This implies that drilling fluids released even at low concentrations are capable of inducing changes in the tissues of fishes endemic in the delta.

Keywords: Drilling, Niger Delta, medial lethal concentration (LC50), median lethal time (LT50)