This work focused on Diplectanum aequans, a gill parasite of Dicentrarchus labrax. Analyzes allowed us to detect factors regulating parasites distribution 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 two sides on each fish. However, the distribution of the number of parasites on gill arches varies according to the total number of parasites. Results differ depending on infection degree and host weight. When parasites are numerous, the individuals are distributed on the gill arches according to an antero-posterior gradient, while with low rates of infection, the parasites are randomly distributed on the 4 arches. The spatial distribution of D. aequans appears to be determined by the differential action of water flow through gill arch and the size of anterior arches. We also proposed a tool in order to reduce the sampling effort and allow optimal exploitation for fish farmers.