Biomonitoriing of Bacoor Bay and Laguna Bay using the micronucleus assay on Oreochromis niloticus (Nile tilapia) erythrocytes

Abstract

Pollution is a major environmental health threat that is brought about by the neglect and incessant discharge of wastes in the environment. These wastes may induce DNA and chromosomal damages and nuclear abnormalities in the organism’s cells and are indicative of the presence of genotoxicants and cytotoxicants. Assessing the possible exposure of organisms’ to such pollutants in the environment is of utmost concern to everyone as such exposures may affect the existence and well-being of the organisms residing in such environments and to human populations dependent on such resources. Hence, this study assessed the occurrence of micronuclei and other nuclear abnormalities in the erythrocytes of the Oreochromis niloticus collected from Bacoor Bay and Laguna Bay. A total of 70 fish samples were collected from the study sites and were examined. Erythrocytes were collected through a caudal vein puncture. Erythrocytes collected were thinly smeared, fixed, stained and examined through microscopy. Approximately 1000 cells were examined and scored for the presence of the nuclear abnormalities that include the micronuclei, binucleated, blebbed, lobed and notched nuclei cells. Results showed that all the nuclear abnormalities were evident in the erythrocytes of the fish samples obtained from the study sites. Blebbed and lobed nuclei were the most commonly seen nuclear abnormalities. Significant differences (p<0.05) of the mean frequencies of binucleated cells and notched nuclei between the two bays were observed. Higher micronuclei frequencies were observed in females as compared to males however such differences were not significant (p>0.05). A strong association was observed between the mean frequencies of blebbed nuclei and micronuclei observed in Bacoor Bay (r = 0.773; p = 0.000) and Laguna Bay (r = 0.535; p = 0.001). The presence of the observed nuclear abnormalities indicates that genotoxicants and cytotoxicants may be present in the study sites. Continuous monitoring for these harmful substances is necessary so as to safeguard the welfare of each organism dependent on such environments.