In this study the authors observed the status of water contamination by crayfish, Cambaroides similis, either alive or dead infected with Paragonimus westermani.

The crayfish used as materials were infected heavily with metacercariae of Paragonimus westermani. The live crayfish were kept in water for a long time, and then the sediments of the water were examined to find out whether or not the liberation of the metacercariae from the body of the crayfish had caused contamination of the water with metacercariae.

Killed crayfish were also preserved in water for some time. Physical stimuli in terms of mederate degree of shaking were added to the preserved water once a day and half amount of the water was replaced with tapped water of same temperature everyday.

Status of the decay of the crayfish, liberation of the metacercariae from the body of the crayfish or contamination of the preserved water by the metacercariae, and numbers of metacercariae harboured in the body of the crayfish were examined everyday. The fate of the metacercariae liberated from the crayfish into water was also observed. Status of the decay of the crayfish, liberation of the metacercariae from the body of the crayfish or contamination of the preserved water by the metacercariae, and numbers of metacercariae harboured in the body of the crayfish were examined everyday. The fate of the metacercariae liberated from the crayfish into water was also observed.

The results of this study can be outlined as follows:

1) No metacercaria was detected in the water which contained live crayfish infected with Paragonimus westermani.

2) The preserved water with dead or killed crayfish was found to be contaminated by the metacercariae of Paragonimus westemani, which had been caused by the decay and dispersion of the flesh of the crayfish.

3) The liberated metacercariae survived for 10 days in the water at 21-27℃.

4) The liberated metacercariae were found to be sinking into water of s.g. 1.000 with average velocity of 35.8 cm per minute.