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.
