The seasonal dynamics of Sphaerospora renicola (Myxosporidia) in carp (Osteichthyes)

TLDR: Premunition (if a hitherto unknown reservoir phase is surviving) or age resistance and/or less chance of coincidence of infective stages and older carps are supposed to be the cause of the rare occurrence of the 3 known phases in carps more than 14-15 months old.

Abstract: We observed 2 different types of the course of incidence of sporogonic phase and blood phase. Type I shows in both phases a maximum in the first summer, a minimum in winter or autumn and a second maximum between late autumn and second summer. In this case the sporulation was especially distinct with the first maximum. Type II starts in the first summer with the blood phase without occurrence of the sporogonic phase (and the swim-bladder phase), which appears only from autumn until the second summer in a form of three peaks. Here the sporulation was successful only in the third peak. Hitherto there has been no other example of that type. The course of incidence, characterized by peaks and valleys, is regarded as an expression of an internal rhythm of different phases of the parasite and not as caused by the declining of infection and by reinfection. Premunition (if a hitherto unknown reservoir phase is surviving) or age resistance and/or less chance of coincidence of infective stages and older carps are supposed to be the cause of the rare occurrence of the 3 known phases in carps more than 14-15 months old. There are some indications of the infection of carps by carps. Carassius au. auratus was ascertained as a new host for S. renicola in a field experiment.