New tools to uncover old tricks: an update on the knowledge on the most successful invasive freshwater helminth, Schyzocotyle acheilognathi

The Asian fish tapeworm (AFT), Schyzocotyle acheilognathi, is a highly invasive and pathogenic parasite of freshwater fishes, present on all continents except Antarctica. Globally, 310 + definitive fish host species have been recorded, with Mexico showing the highest number of reports. Here, we summarize the current knowledge about the biology, distribution, and ecological determinants of this parasite, highlighting key knowledge gaps that could guide future research. Considering Mexico has quite comprehensive records of this parasite (both in host and geographical terms), we propose that this country can be considered as a large-scale ecological laboratory to investigate the environmental variables associated with the parasite's dispersion capabilities in different geographic areas, potentially providing clues on the (unexplored) paths followed by this extremely successful invasive parasite. Using published parasitological data, we implemented exploratory analyses of ecological and environmental parameters to identify factors associated with the occurrence of S. acheilognathi. Temperature, precipitation, and elevation emerged as potential drivers of its distribution, providing a basis for ecological niche modeling and for predicting future range expansions under climate change scenarios. Despite its extensive host range, S. acheilognathi exhibits low genetic diversity-an intriguing feature that may underlie its ecological plasticity and invasive success. We also discuss the growing potential of omics and environmental DNA tools to advance non-destructive detection, clarify host-parasite dynamics, and uncover molecular mechanisms underlying host adaptation and invasion. Integrating these ecological and genomic perspectives will be essential to understand the evolutionary ecology of S. acheilognathi and to anticipate its impacts on freshwater biodiversity in an era of global change.