Monogenean flatworms: petite parasites, mighty models, innovative indicators?

Abstract

Monogeneans are an often overlooked, understudied group of helminths. Even their mere existence has regularly come under scientific scrutiny! Often tiny, and mostly infesting external surfaces of fishes, they receive less research and policy attention than the better known flukes and tapeworms that are often of severe human and veterinary health concern. This is unfortunate, as their direct (one-host) lifecycle gives them a methodological advantage for scientists: the (history of) interactions with their hosts can be studied with less confounding factors than is the case for parasites with a complex lifecycle involving vectors or other intermediate hosts. With over 5700 known species and a cosmopolitan distribution covering a wide range of hosts and infection sites, monogeneans, therefore, present a diverse assemblage of candidate models in various subfields of parasitology [1]. For example, in the African Great Lakes, textbook playgrounds for generations of biologists, we studied them to investigate how host evolution [2] and ecology [3] influence parasite communities. Moreover, especially in captivity or when co-introduced with non-native species, monogeneans can wreak havoc to host populations.

Despite an evident negative connotation, parasites provide numerous ecosystem services. For example, they may act as tags for the history of their hosts. This can be applied in invasion biology, where monogenean parasites can help identify fish stocks [4] and infer routes and mechanisms of introduction [5]. The indicator potential of monogeneans also makes them sentinels for ecosystem-level changes resulting from human intervention [6]. The fact that anthropogenic impacts threaten parasites at least as much as they do their hosts and ecosystems, may even make our favourite flatworms interesting to conservation efforts [7]. They also hold promise in environmental parasitology, to help assess effects of pollution, and even for relatively well-studied systems, this field of parasitology is often still in its infancy [8].

References [1] Vanhove M.P.M., Pariselle A. & Kmentová N. (2024) Monogenean parasitic flatworms. Current Biology 34(22): R1122-R1124. https://doi.org/10.1016/j.cub.2024.10.033 [2] Vanhove M.P.M., Kmentová N., Faes C., Fernandes J.M.O., Hahn C., Hens N., Pariselle A. & Koblmüller S. (2025) Understanding the influence of host radiation on symbiont speciation through parasites of species flocks. Cold Spring Harbor Perspectives in Biology 17(1): a041450. https://doi.org/10.1101/cshperspect.a041450 [3] Kmentová N., Cruz-Laufer A.J., Milec L., Moons T., Heeren S., van den Hoorn E., Thys K.J.M., Makasa L., Chocha Manda A., Masilya Mulungula P., Van Steenberge M., Jorissen M.W.P. & Vanhove M.P.M. (2024) Host lifestyle and parasite interspecific facilitation mediate co-infection in a species-poor host-parasite system. Oikos 2024(10): e10360 https://doi.org/10.1111/oik.10360 [4] Jorissen M.W.P., Vanschoenwinkel B., Pariselle A., Artois T., Danadu C., Huyse T., Kapepula Kasembele G., Muterezi Bukinga F., Šimková A., Snoeks J., Van Sever W., Vreven E., Wamuini Lunkayilakio S. & Vanhove M.P.M. (2025) Do parasite communities differ between invasive and native fish hosts? A case of monogeneans infecting the gills of Nile tilapia. Hydrobiologia https://doi.org/10.1007/s10750-024-05789-8 [5] Kmentová N., Van Steenberge M., Thys van den Audenaerde D.F.E., Nhiwatiwa T., Muterezi Bukinga F., Mulimbwa N'sibula T., Masilya Mulungula P., Gelnar M. & Vanhove M.P.M. (2019) Co-introduction success of monogeneans infecting the fisheries target Limnothrissa miodon differs between two non-native areas: the potential of parasites as a tag for introduction pathway. Biological Invasions 21: 757-773. https://doi.org/10.1007/s10530-018-1856-3 [6] Gobbin T.P., Van Steenberge M., Vranken N. & Vanhove M.P.M. (2024) Worms of change: anthropogenic disturbance changes the ectoparasite community structure of Lake Victoria cichlids. bioRxiv https://doi.org/10.1101/2024.04.14.589059 [7] Vanhove M.P.M., Auwerx J., Kmentová N., Martel A., Nelson A., Terriere N., Van Wichelen J., & Gobbin T.P. (2025) Captive breeding of the critically endangered European weatherfish: a refuge for the conservation-sensitive parasite Gyrodactylus fossilis? The Biologist (Lima) 23(S1): S123-S124 [8] Shigoley M.I., Antoine-Moussiaux N., Jauniaux T. & Vanhove M.P.M. (2024) Parasitology of one of the world's foremost fisheries target species lacks a One Health approach. Hydrobiologia https://doi.org/10.1007/s10750-024-05695-z

Acknowledgment The Authors acknowledge the Czech Science Foundation (GAČR), the Research Foundation – Flanders (FWO-Vlaanderen), VLIR-UOS, the Special Research Fund (BOF) of Hasselt University, the Belgian Federal Science Policy Office (BELSPO), EU SYNTHESYS, and the Swiss National Science Foundation for the financial support.