Hepatoxylon trichiuri (Cestoda: Trypanorhyncha) plerocercoids in cage-reared northern bluefin tuna, Thunnus thynnus (Osteichthyes: Scombridae)
Northern bluefin tuna (Thunnus thynnus) were caught by purse seine boats and brought to a farm for a rearing cycle of 1.5 years. Mortalities occurred in the first weeks of acclimatization at the facility. Parasitological examination revealed plerocercoids of the cestode Hepatoxylon trichiuri embedded in the stomach mucosa. The larvae were found in 28.4% of the fish and the mean abundance was 3.12 per fish. Histopathology revealed disseminated erosion at the site of attachment, atrophy of fundic glands, lymphocytic migration, and hyperplasia of connective tissue in the lamina propria. These symptoms, however, together with the parasite abundance, could not have triggered the mortalities. This is the first record of this parasite in northern bluefin tuna.
Histopathology of Five Species of Didymocystis spp. (Digenea: Didymozoidae) in Cage-reared Atlantic Bluefin Tuna (Thunnus thynnus thynnus)
The first parasitological examinations of Atlantic bluefin tuna Thunnus thynnus thynnus reared in the Adriatic Sea revealed high numbers of different digenean trematodes, belonging to family Didymozoidae. Five species were the most frequently isolated: Coeliodidymocystis, abdominalis, Didymocystis wedli, Koellikerioides internogastricus, K. intestinalis and K. apicalis. Parasites were isolated from gills, gill rakers, intestine, serosa of pyloric caeca, and inner layers of the fundic region of stomach, encysted in pairs in connective tissue capsules originating from host tissue. Gross pathology revealed no pathological changes. Histological alterations comprised tissue reaction resulting in lymphocyte infiltration and formation of a collagenous envelope around the parasite cysts; the intensity of observed reaction depended on the size of the cyst and on the tissue infected. The most notable changes were observed in the intestine under provocation by K. intestinalis, while the most potentially pathogenic didymozoid under fish rearing conditions is D. wedli, which if present in high abundance can induce secondary bacterial infections.
Human exposure to methylmercury from crayfish (Procambarus clarkii) in China
Methylmercury (MeHg) accumulation in aquatic food raises global concerns about human exposure to MeHg. Crayfish is the world’s third largest farmed crustacean species and a favorite aquatic food in many countries. However, human health hazard due to MeHg exposure via crayfish consumption is unclear, partly because appropriate survey data are lacking. We report on mercury concentrations and speciation in edible tail muscle of crayfish collected from restaurants in 23 Chinese cities. On average, MeHg constituted 99.1 % of mercury in tail muscle, and MeHg concentrations were comparable with those reported for fish in China. Variation in MeHg concentrations was not attributable to broad geographic region (i.e., provinces) or tail length. For different populations, potential health risk (characterized by hazard quotient or HQ) of MeHg exposure through crayfish consumption depended largely on crayfish consumption rates. In particular, a health hazard (HQ > 1) was found for high-rate consumers (i.e., 95 %ile or higher) in some cities in the middle and lower reaches of the Yangtze River (MLYR), during the peak consumption season. Our results suggest that more attention should be paid to dietary MeHg intake via crayfish consumption in China, particularly for communities with high consumption in MLYR.