Occurrence of the enigmatic, unicellular Psorospermium organism in severalcultured, sympatric populations of the freshwater crayfishes Procambarus clarkii and Procambarus zonangulus

The parasitic Psorospermium organism was studied in cultured sympatric popu lations of mature Procambarus clarkii and Procambarus zonangulus during fou r consecutive annual crayfish seasons from 1991-1992 through 1994-1995. Mos t P. clarkii were infected while fewer than half of the P. zonangulus were infected throughout the study period. The numbers of Psorospermium were fou r to eight times greater in P. clarkii and showed annual changes not seen i n P. zonangulus. Both crayfishes demonstrate 1-yr life cycles in Louisiana and this seemed to explain the variations seen in Psorospermium dynamics in the two hosts. In general, there was no consistent association between cra yfish size and the number of parasites found in them for either crayfish sp ecies. There was some indication of an association between the presence of infection and the number of parasites found in P. zonangulus.