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

The population structure of the bupyrid isopod Probopyrus floridensis infesting the freshwater shrimp Macrobrachium potiuna from the Pereque River was monthly analysed from January 1996 to October 1996. The parasites, taken from preserved shrimps, were measured and sexed. A total of 635 isopod parasites was obtained from 197 shrimps. The following developmental stages and sexes were recognized within the parasite population: cryptoniscus, bopyridium, immature males, immature females, mature males, mature females, and ovigerous females. The parasitic density fluctuated between 1 (January and May) and 33 (June) parasites per host. The parasitic incidence varied from 1.1% (April) to 97.6% (September). Ovigerous females were observed only in October. The cryptoniscus infestation occurred mainly in June (early winter) and continued for three months. By July (winter), the majority of the parasite population was still composed of juvenile or immature parasites, but from August to October (spring), the adult stages predominated. Probopyrus floridensis reproduces only once a year. Its life cycle is discussed in more detail.