Macroscopic description and histopathological characterization of lesions observed on fish farmed within the Saint-Louis region of Senegal

Abstract

Fish farming, one of the priority sectors in Senegal, is well established in the Saint-Louis region, which offers a high potential, with more than 50% of farms in activity and dispose of a well-supplied hydrographic network and support services (executive agencies and university). However, this development is correlated with a variety of health problems observed in the most cultured fish in Senegal (tilapia and catfish). The objective of this study is to describe the clinical cases and lesions observed in tilapia (Oreochromis niloticus) and catfish (Clarias gariepinus), reared in fish farms in the Saint-Louis region. The study started with surveys followed by the description of clinical signs and macroscopic lesions observed on sick or freshly dead fish and then by bacteriological and histopathological examinations. Results from the investigations have highlighted, firstly, the risks of chemical or microbiological contamination related to the proximity of habitations to fish farms (environmental contamination), and secondly, the fluctuations of physico-chemical parameters and the degradation of water quality, feed quality and its storage conditions. The results showed that clinical cases are associated with lesions either localized on different parts of the body (fins, gills, eyes), or generalized to external and internal organs. Cases of malformations and swollen masses were also noted. Bacteriological analysis revealed the presence of Aeromonas hydrophila, in co-infection with Vibrio sp. Histology confirmed multiple necrotic, hemorrhagic and cystic lesions on skin and in other organs. The observed clinical cases are associated with the poor conditions of fish farming and of the local environment in the study area.