抄録
Ichthyophthirius multifiliis Fouquet, 1869, is one of well-known parasitic ciliates on freshwater fishes. I have studied its reproduction at various water temperatures by both indoor and outdoor observations. Infection was obtained by placing healthy individuals of orange race of carp together with diseased gold-fishes. A Sénô-Tauti's serial incubator was used in the laboratory, and a small concrete pool outside it.
The results obtained are summarised as follows: -
1. The optimum temperature for the reproduction of Ichthyophthirius is at about 14-17.5°C.
2. The encysting occurs within a temperature range from 3.1° to 25°C. The reproduction does not almost entirely take place at water temperatures of 1.2° and 2.1°C.
3. The division of the cysts is completed within a day at temperatures ranging from 16.2° to 25°C, but over a day at temperatures ranging from 14.0° to 5.8°C.
4. The minute free-living individuals fresh from the cysts are of frail constitution and easy to perish within a day.
5. Ichthyophthirius attains maturity in about 2 weeks at 14°C, about a week at 20°C, and 20 days at 7°C.
6. It appears to undergo division on the fish skin.
7. It probably passes the winter season by making life-cycle, from reproduction within the cyst to growth on fish-body, at lower rate.
8. The rate of reproduction appears to be higher in a darker place.
