engleski

Intraspecific genetic diversity of Didymosulcus katsuwonicola parasitising bluefin tuna (Thunnus thynnus) gills

In total five loci of a nuclear (ITS1, ITS2) and mitochondrial (COX, COI, ND1) DNA were used to asses intraspecific genetic diversity of a didymozoid digenean species Didymosulcus katsuwonicola, parasitising gills of Atlantic bluefin tuna (Thunnus thynnus). It is the most prevalent and abundant parasite species in tuna reared in the Mediterranean, whose population numbers have been shown to decline during the rearing period of one and a half years. These hermaphroditic didymozoids are propagated to bluefin as cercaria through ingestion of infected small pelagic fish and cephalopods that further migrate from the digestive system of the final host to its highly vascularized gill tissue. In gills they encyst always in pairs, although they are hermaphrodites that do not need each other for reproduction. Generally, there is a lack of knowledge about pathways of their migration from gut to gills or mechanisms that cercaria might use to find each other in gill tissue and encyst in pair. This for, our goal was to assess if two individuals of D. katsuwonicola encysted in a single cyst share the same genotype, how much such genotype differs from the genotypes of individuals from other cysts present in the same or different host. Results showed that most of individuals encysted together have similar size, with only few exemption when juvenile individuals were found encysted alone or together with an adult. This suggests that formation of the early tissue cyst precede the “meeting” of two individuals. Intraspecific diversity showed that intricate infection and reproduction mechanisms exist in this didymozoid, presumably as an adaptation for successful fulfillment of their life cycle.

Bluefin tuna ; Thunnus thynnus ; Digenea ; Didymosulcus katsuwonicola

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