BIOCHEMICAL EFFECTS OF CRUDE OIL EXPOSURE AND BIOAUGMENTATIONON GILLS AND LIVER OF JUVENILE NILE TILAPIA (OREOCHROMIS NILOTICUS)

Abstract

Exposures of aquatic organisms to crude oil have been shown to impact on fish physiology and sometimes leading to large scale mortality. Specific objectives of the research were todetermine the LC50 and LC90 of crude oil on Juvenile Nile Tilapia, investigate toxic effects of crude oil pollution on the gills and liver of Oreochromis niloticus (Nile Tilapia) through biochemical and histological evaluation anddetermine the efficacy of bioaugmentation using mixed culture of Bacillus sphaericus and Alcaligenes eutrophus on survival and antioxidant enzymes in the gills and liver of Nile Tilapia in crude oil polluted pond water (test media). The LC50 of crude oil in this study was 0.25% v/v and LC90 was 0.35% v/v. The study showed that activities of various antioxidant parameters in gills and liver (catalase, superoxide dismutase and reduced glutathione) were significantly inhibited after exposure of fish to lethal crude oilconcentrations, when compared with fish in clean pond water (negative control) and those under bioaugmentation treatment. The level of malondilaldehyde (MDA), an important indicator of lipid peroxidation, in gills and liver of fish exposed to lethal crude oil concentrations increased when compared with the negative control. Also, the exposure of the test media to different concentrations of crude oil reduced the water dissolved oxygen concentration, while increasing the conductivityand pH. The histology of tissues shows no visible lesion in the gills of fish under bioaugmentation and clean water treatments, but those exposed to lethal concentrations of crude oil suffered severe erosions of the gill mucosa and secondary lamellae. No visible lesion in the liver of fish in clean pond water while a mild diffuse vacuolation of the hepatocytes was seen in the liver of fish under bioaugmentation treatment compared with the severe diffuse hepatic vacuolar degeneration in the liver exposed to lethal oil concentration. The bioaugmentation treatment also shows a reduction in the mortality rate of fish compared with those in crude oil polluted water.