The toxicity of drilling fluid XP-07 on gills of three life stages (fry, fingerling and post fingerling) of Tilapia guineensis was evaluated in a 96h static bioassay. The mortality rates of the organisms were determined using the same concentrations of XP-07 in all the life stages. At the end of 96h, the gills were examined for histopathological changes. The 96h median lethal concentrations for fry (Fr), fingerlings (F) and post fingerlings (PF) were 5.03, 7.77 and 6.93% XP-07 respectively. The median lethal time values decreased as concentration and time of exposure increased. The histopathological studies carried out on gills of T. guineensis showed injuries, which increased progressively with the concentration of the fluid. The fry stage was the most susceptible to the drilling fluid. This states the need for care to be taken in handling drilling fluids in Niger delta, since this area serves as breeding and nursery ground for several fish species.
toxicity; histopathology; Niger delta; drilling, fluid; median lethal concentration(LC50); median lethal time (LT50); Teleost
