RÉSUMÉ
Pathological changes are regarded as a standard technique to monitor the effects of pollutants in marine animals. Histopathological examination of the population of green mussel Perna viridis (L.) from four sites in Pakistan, namely, Manora Channel, Rehri Creek, Sandspit Backwaters and Bhanbore was conducted. The first three sites are on the Karachi coast, whereas the fourth one, Bhanbore is situated outside Karachi, and is considered to be less polluted. Two types of parasites, Rickettsia-like organisms and metacestode were found in the mussels studied. In the present study, we observed various pathological lesions, such as inflammatory responses, granulocytomas, lipofuscin pigments, vacuolation in the digestive gland and gonads, lamellar fusion and dilated hemolymphatic sinus in the gills of P. viridis. These observations indicate the extent of environmental pollution in the studied areas. Although, Bhanbore is considered to be relatively less polluted compared to other three sites, the present results have revealed that the waters of Bhanbore are also polluted as evidenced by the pathological changes observed in the mussels collected from there.