The population structure of Probopyrus floridensis (Isopoda, Bopyridae), aparasite of Macrobrachium potiuna (Decapoda, Palaemonidae) from the Pereque River, Parangua Basin, Southern Brazil

The population structure of the bupyrid isopod Probopyrus floridensis infes ting the freshwater shrimp Macrobrachium potiuna from the Pereque River was monthly analysed from January 1996 to October 1996. The parasites, taken f rom preserved shrimps, were measured and sexed. A total of 635 isopod paras ites was obtained from 197 shrimps. The following developmental stages and sexes were recognized within the parasite population: cryptoniscus, bopyrid ium, immature males, immature females, mature males, mature females, and ov igerous females. The parasitic density fluctuated between 1 (January and Ma y) and 33 (June) parasites per host. The parasitic incidence varied from 1. 1% (April) to 97.6% (September). Ovigerous females were observed only in Oc tober. The cryptoniscus infestation occurred mainly in June (early winter) and continued for three months. By July (winter), the majority of the paras ite population was still composed of juvenile or immature parasites, but fr om August to October (spring), the adult stages predominated. Probopyrus fl oridensis reproduces only once a year. Its life cycle is discussed in more detail.