Basic studies on the control of blood fluke infection of Pacific bluefin tuna

首先，从太平洋蓝鳍金枪鱼心脏心室中发现第二种血吸虫，并将其描述为Cardicola opisthorchis n。其次，建立了新的鉴别方法，并将其应用于卵的鉴别。orientalis与C.后睾吸虫的形态，并计算鳃中的卵数。第三，部分阐明了侵染循环。也就是说，这两种血吸虫被发现在少年金枪鱼转移到外面的网箱后45天，一个星期后，吸虫成熟，并在一个多星期后产卵。第四，C.用吡喹酮（PZQ）7.5mg/kg鱼体重或更高剂量连续口服3天，对金枪鱼体内的后睾吸虫进行杀灭。用药后1个月证实再次感染。金枪鱼体内PZQ浓度在给药后24 h降至检测不到水平（0.02 μg/L）。扫描电镜观察表明，两种血吸虫的体壁肿胀、收缩，并形成许多细小的沟嵴。opisthorchis，而C. orientalis，在皮层上形成许多特征性的小孔。

Firstly, a second blood fluke species from Pacific bluefin tuna was found from the heart ventricle and described as Cardicola opisthorchis n. sp. Secondly, new methods were developed to distinguish eggs of C. orientalis from those of C. opisthorchis morphologically, and to count the number of eggs in the gills. Thirdly, infection cycle was partly elucidated. Namely, both species of blood flukes were found in juvenile tuna 45 days after transfer to outside net cages; one week later, flukes were matured and laid eggs after one more week. Fourthly, C. opisthorchis was eradicated from tuna with oral administration of praziquantel (PZQ) at 7.5 mg/kg fish body weight or more for 3 consecutive days. Reinfection was confirmed 1 month after medication. PZQ concentration in tuna decreased to the undetectable level（0.02 μg/L）24 h after administration. Lastly, SEM observation of the two species of blood flukes shows swelling and contraction of the tegument and formation of many minute furrowed ridges in C. opisthorchis, while in C. orientalis, many minute holes were characteristically formed on the tegument.