Abstract

Cultivation of the "ostión del norte", Argopecten purpuratus, is an important economic activity in the 3rd and 4th Regions of Chile. Studies of disease were undertaken on wild scallops to gather baseline information on healthy populations. However, as cultivated scallops are kept at higher densities than the wild populations, the occurrence and prevalence of parasites and tissue pathology differed as indicated in this study that compares the types of parasites and their prevalence in wild and cultivated scallops from Tongoy Bay, a major center for scallop cultivation. In January 1999, 151 cultivated and 154 wild scallops were examined histologically and via scanning electron microscopy (SEM). The same parasite taxa, as well as granulomas, were found in both populations, but their prevalence differed. The granulomas were small, with no apparent etiology, but the cultivated population harbored significantly more lesions than the wild population. The only parasites found were a prokaryote in the digestive gland and the ciliate protozoan Trichodina sp. on the gills of the scallops. Trichodina did not seem to elicit a host response and its prevalence was significantly higher in the cultivated scallops. The prokaryote, a rickettsiales-like organism (RLO) was observed as basophilic inclusions in digestive gland tubule epithelial cells. The intensity of infection was low, but significantly higher in the wild stock. No host reaction was seen, and the prevalence showed no significant difference between the two populations. The infection with RLOs was therefore independent of the source of the scallops, unlike the Trichodina or the granulomas, which were significantly more prevalent in the cultivated population.