Estudo das causas da mortalidade de vieiras Nodipecten nodosus (MOLLUSCA:BIVALVIA) em Angra dos Reis, Rio de Janeiro

Abstract

The scallop Nodipecten nodosus is one of the most economically valuable bivalves cultivated in Brazil. Until 2017, the largest national production of scallops occurred in Ilha Grande Bay (RJ), when consecutive mortality episodes began, severely compromising production and leading to significant economic losses. Recurrent mortalities represent an obstacle to the continuity and sustainability of the sector. Mortality events in bivalves have already been recorded in bivalve populations on other continents, the causes of which have been associated with both specific infectious agents and a combination of factors. This study aimed to analyze the health of scallops and search for potential agents associated with successive mortality events. Between May and June 2024, scallops were collected from a farm in Angra dos Reis (N = 50) a few days after a mortality event and from Cabo Frio (N = 20, control area). The animals were opened, and tissues were removed and preserved for diagnostic procedures: PCR for detection of the protozoan Perkinsus spp. and oyster herpesvirus (OsHV-1); and histological sections for assessment of overall health status. The results showed sporadic, non-pathological presence of some microorganisms in scallops from Angra dos Reis: ciliates in the intestinal lumen, unidentified protozoa, possibly phagocytosed, in the intestinal epithelium, and copepods in the stomach lumen.Perkinsus spp. or herpesvirus were not detected. All animals from Angra dos Reis showed significant changes in the digestive gland, the organ responsible for nutrient assimilation, characterized by atrophy of the digestive tubules and accumulation of yellowbrown material in the lumen. In the epithelium of the stomach and intestine, there was disorganization of the architecture, with loss of cohesion between cells and hemocyte infiltration (47%). In the mantle epithelium, some regions showed exacerbated melanization (42%). The presence of infiltrated cells in the connective tissue of various organs was observed (26%), with anaplastic, hypertrophied characteristics and a high nucleus-cytoplasm ratio, associated with the presence of mitotic figures, characterizing cell proliferation. These characteristics are typical of disseminated neoplasia in bivalves, which may have a hemocyte origin. In Cabo Frio, there was only an accumulation of yellow-brown material (40%) without atrophy of the digestive tubules and intense melanization in the mantle (10%). It is not possible to conclude that the histopathological changes detected are the cause of scallop mortality, but they indicate a situation of physiological stress in the animals. If confirmed, disseminated neoplasia would be the first case in pectinids.