New findings in research on the oomycete parasites of carp

Researchers from the Fish Pathology and Parasitology research group confirmed the presence of a total of five Thelohanellus species, three of which—Thelohanellus serosae, T. borkhanuddini, and T. paranikolskii—were described as new species to science. Species identification was supported by detailed morphological, morphometric, and molecular analyses, providing a solid taxonomic basis for interpreting the results.

A key finding of the study is the experimental elucidation of the life cycle of one of the examined species, T. borkhanuddini, supported by molecular data. During the investigations, the actinospore stages were also successfully identified, and it was confirmed that a species of oligochaete worm (Branchiura sowerbyi) serves as an alternative host in the parasites’ development. The actinospores appeared in several forms with different morphologies, providing new data on the developmental biology of Thelohanellus species.

The research also confirmed the presence of the previously known species T. hovorkai and T. nikolskii in domestic carp populations. The results contribute to a better understanding of the species diversity, life cycle, and distribution of mucosporidian parasites of carp, which in the long term supports the development of more effective disease prevention and management strategies in Hungarian aquaculture and the protection of fish populations in natural waters.

The research was supported by the Stipendium Hungaricum Program. A paper summarizing the research results was published in the journal Aquaculture Reports: https://doi.org/10.1016/j.aqrep.2026.103380.