Gill metazoan parasites of tunas (Scombridae: Thunnini) from the western Mediterranean Sea: systematics, assemblages and use as biological tags

This PhD thesis describes the metazoan gill parasites of five tuna species from the western Mediterranean Sea, and analyses their assemblages, comparing the results with existing data from the Mediterranean Sea and other seas. It is the first comparative analysis of the parasites of tunas, and the most complete data collection on the gill parasites of the Atlantic and Mediterranean tunas. The final goal of this work is to achieve information to evaluate the usefulness of the parasites of tunas as tags for studies on host biology, ecology and migrations. Between 2006 and 2011, 356 fish were sampled from seven localities of the Mediterranean Sea: 72 Auxis rochei (Algerian Sea, Gibraltar Strait); 156 Euthynnus alletteratus (Algerian Sea, Balearic Sea, Gibraltar Strait); 35 Katsuwonus pelamis (Alboran Sea, Balearic Sea); 30 Thunnus alalunga (Balearic Sea); 63 Thunnus thynnus (Levantine Sea, Sardinian Sea, Tyrrhenian Sea). Overall, 39 parasite species were found, belonging to Monogenea, Trematoda and Crustacea, adding 30 new records for this area and 14 new host records; didymozoid trematodes were the dominant group. A number of parasite species was shared between hosts, showing the existence of a wide parasite metassemblage. The rich metazoan parasitofauna found in the gills of the five tuna species seems to be a promising tool to infer information on the host biology and ecology. Didymozoids are likely the most useful group, but also monogeneans can be used with some caution.