Abstract

As a part of observation on the suitability as a second intermediate host of Clonorchis sinensis, various infection experiments were tried to Cyprinus carpio nudus. The results obtained were summarized as follows: The cercariae which attempted to contact with Cyprinus carpio nudus in the water were observed under the stereomicroscope. After contact, cercariae began to separate its tails from the bodies at 4 minutes increasingly, and then the number ranged to 80 percent at 13 minutes after the encounter. But very few cercariae could actually invade into the epidermis of the fish. When Cyprinus carpio nudus were exposed to a number of cercariae in the beaker, only a few cercariae could invade through the epidermis. Most of the invaded cercariae were killed before forming the cyst. Also rare encysted cercariae were found to be dead within 48 hours. Cyprinus carpio nudus were reared with Parafossarulus manchouricus shedding numerous cercariae in the indoor aquarium. When observed after 12 days, to determine the susceptibility, no metacercaria was found infected. Cyprinus carpio nudus were reared with Parafossarulus manchouricus shedding numerous cercariae in Kimhae lake for 2 months in summer of 1982, in order to check the natural infection. No metacercaria of Clonorchis sinensis was found from the fish. In the cases of control fish, Pseudorasbora parva, numerous cercariae were inspected on the course of invasion through epidermis of the fish under the stereomicroscope. And many metacercariae were also found from the fish whenever they were kept in beaker, indoor aquarium, or the lake for natural infection. The results suggested that Cyprinus carpio nudus might not be proper intermediate host of Clonorchis sinensis.