The toxicity effects of crude OIL were investigated in the laboratory. Triplicates of (T1) 0.25mg/l, (T2) 1.0mg/l, (T3) 2.25mg/l, (T4) 5.0mg/l and (T5) 7.5mg/l concentration of crude OIL exposed to Sarotherodon melanotheron species. The acute toxicity test of crude OIL when tested against Sarotherodon melanotheron revealed that the derived toxicity index LC50 was 0.925mg/l. On computing Toxicity Factor (TF), using 96 hours. LC50, crude OIL was found to be very toxic to the Sarotherodon melanotheron juvenile. The mean frequencies of micronucleus in S. melanotheron exposed to different concentration of crude OIL ranged from 3.01±0.50 – 27.48±2.71. The lowest value was 3.01±0.50 in T0 (control) while the highest value of 27.48 ± 2.71 wasrecorded in fishes exposed to (T5) 7.5mg/l test solutions. The results obtained from micronucleus test showed that T5 had the highest number of micro-nucleated cells followed by T4 while T1, T2, T3, and T0 significantly increased with the concentration across the test chemical. Sarotherodon melanotheron showed various degrees of sensitivity in monitoring genetic damage especially in the normal nucleus (NN). The chromosomal aberrations indicate formation of vacuolated nucleus (VC), micronucleus (MN) and bi-nucleated cells (BN) showed marked increase in occurrence in the following concentrations of occurrences; T1, T2, T3, T4 and T5, respectively. Test solution of concentration T5 (7.5mg/l) was observed to possess fish with highest level of micronucleus frequencies followed by T4 (5.0mg/L). There were significant differences in increasing T5 having the highest number of micro-nucleated cells (MN) with a trend in increasing bi-nucleus cells (BN), polymorphic nucleus (PM), kidney shape nucleus (KN) and bleb nucleus (BLN) cells, respectively, as the concentration of the test chemical increased. The results also showed that there was a significant difference in the effects of the T5 and other test concentrations (T1, T2, T3, T4 and T0). The response of Sarotherodon melanotheron established that is a better model for bioassay test used as a pollution bio indicator. Pollutants even in a very low concentration if present for a long duration may affect the nucleus. Hence, the use of any kind of substances such as crude OIL products and synthetic chemicals in aquaculture field should be carefully monitored and used under proper guidance.