Sphaerospora molnari is a microscopic endoparasite of carp (Cyprinus carpio) in pond cultures and natural freshwater habitats in Central and Eastern Europe.

Affected tissues show marked dystrophic changes and necrosis,[4][5][6] causing secondary bacterial infections and resulting in osmoregulatory and respiratory failure.

Specific PCR[10] and qPCR[13] assays exist and are able to differentiate the species from congeners occurring in the same host and quantify parasite numbers.

Ganeva et al.[15] demonstrated the effectiveness of certain in-feed treatments against S. molnari, with reduced parasite numbers in the blood of carp receiving diets enriched with certain parasiticidal and immunostimulatory substances.

Of more than 2600 known myxozoan species, only 55 life cycles have been elucidated to date,[16] and very few (3-4) are continuously perpetuated in research laboratories, as their maintenance is laborious and time-consuming, with the production of fish-infective spore stages in oligochaete or polychaete cultures spanning over several weeks or months.

An experimental research model for proliferative stages is urgently required for myxozoans, for which no treatments are available but which appear to be an important group of fish parasites on the rise.

First transcriptomic datasets of blood stages have been studied with regard to its arsenal of proteolytic enzymes,[18] which have demonstrated a great potential for vaccine design in other parasites.