Effect of different concentrations of biodegrader (<i>Bacillus subtilis</i>) on the survival of fingerlings in crude oil polluted environment

Abstract

The role of various concentrations of hydrocarbon degraders (Bacillus subtilis) in the survivability of Clarias gariepinus reared in hydrocarbon polluted aquaria was investigated under laboratory conditions using standard microbiological and analytical protocols. Six aquaria containing ten fingerlings each were contaminated with 100ml of crude oil and different amount (5ml, 10ml, 15ml and 20ml) of hydrocarbon degraders (Bacillus subtilis) in broth culture were introduced into each of the aquarium. The set-up which was adequately aerated was monitored for 21 days for survivability of the fingerslings. The results revealed changes in swimming performance and feeding pattern of the fingerlings after crude oil contamination. Reduction in swimming was observed in those fingerlings with less hydrocarbon biodegraders. Similarly, the feeding habit of those fingerlings with less hydrocarbon degraders decreased significantly. The aquarium with no biodegrader recorded 3,2 and 3 deaths on the 1^st, 2^nd and 3^rd week respectively while the aquarium with the highest biodegraders recorded 2, 2 and 0 death on the 1^st, 2^nd and 3^rd week respectively. The rate of death of the fingerlings revealed that increase in hydrocarbon biodegraders in the aquarium increased the survival of the fingerlings in the aquarium. Specifically, it was observed that aquarium with the highest biodegrader (20ml) recorded the lowest mortality of 40% at the end of 21 days. No mortality was recorded in aquarium with no crude oil contamination. This study revealed that in the aquarium with highest hydrocarbon degraders, the effect of crude oil was quickly neutralised thus eliminating the mortality of the exposed fingerlings on the third week of the experiment.