engleski

Parasite communities in the wild and reared bluefin tuna (Thunnus thynnus) in the Adriatic Sea

During the three-year period parasitofauna of tuna was monitored at the entrance of fish in cages (wild tuna) and at the end of the rearing process at the “ harvest” (reared tuna) or during outbreaks of mortalities. Vast and divers parasitic groups were identified, never showing to be implicated in diseases outbreaks. Two new parasitic species, Ceratomyxa thunni (Ceratomyxidae, Myxozoa) and Microsporidia sp., are isolated and described for the first time in bluefin tuna. Trematodes are the most abundant and prevalent parasitic group in both wild and reared fish. Two species of monogeneans are regularly isolated: the capsalid Tristomella laevis and polypisthocotylean Hexostoma thynni, while digeneans stand as the most divers parasitic group comprising 6-10 different Didymozoid species. Nematodes are composed of Anisakis sp. third stage larvae and the camallanid Oncophora melanocephala and Cestoda of plerocercoids of Hepatoxylon trichiuri (Cestoda: Trypanorhyncha) and blastocysts of Eutetrarhynchus lineatus (Heteroacanthoidea, Trypanorchyncha). Pennella filosa (Pennellidae, Copepoda) was the only crustacean isolated. Comparing parasite communities of wild and reared fish, a sudden decrease in the number of parasites was observed in tuna after short time of rearing. This trend is unexpected because fish are daily fed with fresh baitfish that enables the propagation of parasitic developmental stages to tuna. The cause could be presumably related to the immunity burst through balanced food or to unfavorable abiotic condition for the parasites in the new environment.

Adriatic Sea ; bluefin tuna ; parasites

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