Multiple Infestation of Ectoparasitic Isopods Tachaea chinensis
We report on the occurrence of multiple infestation by the ectoparasitic isopod Tachaea chinensis on the freshwater shrimp Palaemon paucidens in Japan. The number of parasites per host was zero to nine at St.1 and zero to three at St. 2. A significant positive correlation was observed between the prevalence of isopods on shrimp and the mean number of these parasites per host. In a laboratory experiment in which individual shrimp of three size groups were reared for seven days with different numbers of isopods from three matching size groups, the survival rate of hosts was 100% with one T. chinensis, 90–100% with two, 50–80% with four, and 10–40% with eight. These results suggest that the presence of two or more parasites negatively affects the hardiness of the host, increasing shrimp mortality and potentially reducing their density in nature.
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