A Long-Term Monitoring Survey of Diplectanum aequans (Wagener, 1857) Diesing 1858, Parasite of the European Cultured Seabass Dicentrarchus labrax (Linnaeus, 1758) (Pisces: Teleostei) from Corsican Fish Farms

This work focused on Diplectanum aequans, a gill parasite of European seabass Dicentrarchus labrax. The analyses allowed us to detect factors regulating parasite distributions on Corsican fish farms and to highlight the ecological structure of D. aequans communities on gills of fish. The study of parasite distribution showed that bigger fish appear more parasitized and that the infection dynamics of D. aequans can be explained by several factors such as biotic factors or farm environment conditions. The study of gill repartition of D. aequans showed that parasites tend to have a homogeneous distribution with no statistically significant difference in infection between the two sides of fish. However, the distribution of the number of parasites on gill arches varied according to the total number of parasites. The results differ depending on infection degree and host weight. When parasites are numerous, the individuals are distributed on the gill arches according to an anterior-posterior gradient, while with low rates of infection, the parasites are randomly distributed on the four arches. The spatial distribution of D. aequans appears to be determined by the differential action of water flow through the gill arches and the sizes of anterior arches. We also proposed a tool to reduce sampling effort and allow optimal exploitation for fish farmers.