Toxicity of drilling fluid XP-07 on microbial load and survival of Oreochromis niloticus fingerlings

Static bioassays were carried out in the laboratory for 96h to investigate the effect of Parateq a synthetic base mud on the fingerling of Orechromis niloticus and their microbial population. The fingerlings were exposed to different concentrations (0, 1000, 3000, 5000 and 9000Mg/l) of drilling fluid. Fish mortality data were recorded at 24, 48, 72 and 96h and analysed using Finney’s Probit Analysis method to calculate LC50 values (concentration of drilling fluid in water that will kill 50% of the fish population in 96 hours). The 96h LC50 was 2210Mg/l.The mortality increased with increase in concentration, while, the lethal times decreased as concentration increased. The bacterial biomass ranged from 1.59 x 108 to 6.0 x 106CFU/ml while fungal biomass ranged from1.0 x 103 to 2.1 x 104 CFU/ml. Results revealed that there was an increase in fungal biomass with increase in mud concentration and a decrease in bacterial biomass with increase in mud concentration