Epidemiology of gnathiid isopods on red mullet (Mullus barbatus barbatus) along the Tyrrhenian Sicilian coast (Mediterranean Sea)

Fishing, reducing the density of fish, might decrease the efficiency of parasite transmission. The present study aims at examining the presence of gnathiid isopods on a wild fish species, the red mullet, under the influence of trawling activity by comparing epidemiological data of trawled and no-trawled areas. The potential impact of gnathiids on the red mullet within a no-trawled area (NTA) of the Southern Tyrrhenian Sea (Central Mediterranean Sea) has been assessed examining epidemiological indices in relation to season, sex, age and host condition. The spatial distribution of prevalence in the study was heterogeneous with the bulk of gnathiids found inside the NTA. Similarly, the intensity and abundance showed values significantly higher inside the NTA than outside. Inside the NTA temporal variations of gnathiid infestation were evident, with the lowest prevalence and intensity during winter but without a seasonal pattern. Gnathiids infection is not related to the sex and age of the red mullet and does not influence negatively the host condition. The occurrence of gnathiids, despite being temporary and generalist parasites, strongly reflects the host density and site protection level.