Viability of metacercariae of Clonorchis sinensis in frozen or salted freshwater fish.

Metacercariae of Clonorchis sinensis were collected from freshwater fish (Pseudorasbora parva) after storage in a freezer at -12 degrees C for 10-20 days, in a freezer at -20 degrees for 3-7 days, or treating with heavy salt (fish/salt = 10 gm/3 gm) at 26 degrees for 5-15 days. The metacercariae from the frozen fish were inoculated into 30 rats and eight rabbits, and those from the salted fish into 33 rats. Metacercariae from freshwater fish stored at -12 degrees for 10-18 days or -20 degrees for 3-7 remained viable and infective. Moreover, those kept at the heavy salt concentration for 5-7 days remained viable and infective. These findings indicate that freezing or storing infected freshwater fish in heavy salt may not be effective in the prevention of clonorchiasis. However, it appears that refrigeration, or keeping the fish in salt for longer periods, may be suitable for prevention of the infection.