Phylogenetic position and new locality record of Salsuginus seculus (Dactylogyridae) associated with Gambusia affinis in its native range in the USA

In this study, we document the presence of the monogenean Salsuginus seculus (Mizelle & Arcadi, 1945) Murith & Beverley-Burton, 1985, parasitising Gambusia affinis (Baird & Girard, 1853), a poeciliid fish native to the River Mississippi and Gulf Coast drainages, within its native range in the River North Fork Guadalupe and the River Brazos Basins in Texas, USA. This marks the fourth recorded locality of S. seculus in Texas, expanding its known distribution. Morphometric comparisons show that measurements of S. seculus from Texas largely overlap with previous reports, though some size variation is observed in specimens from the western USA and those associated with G. affinis populations in Japan. Phylogenetic analysis of 28S rDNA sequences places Salsuginus as a sister taxon to a monophyletic group of dactylogyrids, including Gussevia, Sciadicleithrum, and Parasciadicleithrum, all from Neotropical Cichlidae. Given the invasive potential of G. affinis, we highlight the importance of monitoring for potential co-introductions of monogeneans, such as S. seculus, into novel habitats, which may impact native fish communities. The molecular data provided in this study will be essential for tracking and identifying S. seculus in non-native regions, aiding in future invasion assessments.