A review of Salsuginus seculus (Platyhelminthes: Monogenean) in the western mosquitofish (Gambusia affinis) from Texas

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Western mosquitofish (Gambusia affinis) are cosmopolitan in warmer climates and can serve as a host for a number of parasites. The gill monogeneans from this host are especially interesting because of the very low species diversity that has been reported in the literature. In the United States alone, only a single species, Salsuginus seculus, is reported from the gills of fish collected across the country. To assess the validity of a single species on the gills of G. affinis, fish were collected from 11 geographically-distant aquatic systems in Texas and surveyed for monogenean infections. The gill monogeneans were then subjected to morphological and molecular analyses. Preliminary analyses suggested that more than one species of monogenean may be infecting the gills of G. affinis in Texas. Morphologically, most of the monogeneans resemble S. seculus, but parasites from a few locations exhibited anatomical differences that did not conform to the description of S. seculus. They are smaller in overall size and differ in their opisthaptor, including the size of the hamuli and the length of the haptoral bars. Sequence analysis on these parasites was performed to determine if consistent patterns of genetic differences exist between specimens collected from the various locations. Based on analysis of a partial 28S rRNA gene region, sufficient support is lacking to distinguish these parasites as different species.