engleski

Biodiversity of Didymozoid trematodes in reared bluefin tuna (Thunnus thynnus)

Tuna (Thunnus spp.) comprises the most valuable finfish aquaculture product currently recognized around the world, with two main methods of rearing processes in use. The most common is the fattening process where fish are kept in captivity for 6-10 months, practiced in the Mediterranean, Australia, Mexico and Japan. In the Adriatic Sea however, smaller specimens are caught and reared for a longer period of time (up to 3 years) in order for fish to gain 50-80 kg of weight for marketable sale. Over the period of 2002-2006, parasitological examination was done on newly caught tuna specimens, one/ two-years-reared fish, harvested tuna and occasional mortalities. Digenean trematodes belonging to Didymozoa family were isolated and identified upon Yamaguti S (1958, Systema Helminthum, Interscience publishers inc., London, UK ; 1970, Digenetic trematodes of Hawaiian fishes. Keigaku Publishing Co. Tokyo, Japan). 63 Didymozoidae were also analyzed for the molecular variation using mitochondrial (COI) and genomic markers (28S rDNA and ITS). 44 specimens were collected from the Atlantic bluefin tuna reared in the Adriatic Sea pans, and 19 were sampled from the Pacific bluefin tuna reared in the Gulf of Mexico. Prevalences and abundances were determined according to Bush AO et al. (1997, Journal of Parasitology, 83: 575-583). Didymozoid digeneans accounted for the larger part (60%) of tuna overall parasitofauna, showing variable impact on the general tuna health. The most prevalent and abundant species were Didymocystis wedli in the gill tissue and Koellikerioides intestinalis in the intestine submucosa, respectively. In contrast with previous results on genetic diversity of digenea Cradicola forsteri and monogenean Hexostoma thynni from four tuna species, our results showed evidence in favour of genetic divergence between didymozoids from the Gulf of Mexico and the Adriatic Sea, respectively.

bluefin tuna ; didymozoidae

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