Supplemental diagnosis of Gyrodactylus fairporti Van Cleave, 1921 (Monogenea) from 1 month old black bullhead (Ameiurus melas) in riverside pools in Wisconsin.

Samples of Gyrodactylus fairporti Van Cleave, 1921 from young-of-the-year black bullhead (Ameiurus melas) stranded in riverside pools of the Black River (La Crosse County,) WI, USA, are used to supplement the species diagnosis, including new details on the marginal hook sickles, the male copulatory organ (MCO), and 18S rRNA gene sequence data. The anchors of G. fairporti are relatively long and thin, 58.2 ± 1.2 μm in length; roots 15.5 ± 1.0 μm; shaft 38.1 ± 1.5 μm; point 31.3 ± 1.5 μm. The ventral bar is 19.4 ± 0.4 μm wide and 5.7 ± 0.9 μm long, with small anterolateral processes, 2.0 ± 0.6 μm long, and an almost rectangular posterior shield 15.5 ± 1.1 μm in length. The marginal hooks are 29.2 ± 1.0 μm long, with the handle 23.9 ± 1.2 μm in length. These measurements are similar to those reported from Iowa and Alabama, with the additional observation of the anchor point bending outwardly halfway along its length. The marginal hook sickle blade leaves the base angled ventrally away from the longitudinal axis; the sickle point is short; the toe has a rounded shelf and the heel is small, thin, and rounded. The MCO has eight small spines, two large ones laterally and the others of various lengths, with two of the smallest spines being slightly out-of-line compared with all the others. The taxonomy of G. fairporti is compared to Gyrodactylus ictaluri Rogers, 1967 and G. nebulosus Kritsky & Mizelle, 1967, the other two species known from captive and wild ictalurids endemic to North America. The three species all have a relatively compact ventral bar with short anterolateral processes, a short almost rectangular ventral bar membrane, an MCO with up to eight small spines of varying length, and a hook sickle angled ventrally. Diagnostically, the species are readily identified by the total length and shape of the anchors. G. fairporti bears the longest (53-65 μm) and most slender anchors of the trio, G. nebulosus intermediate (49-51 μm) and G. ictaluri with the shortest and stoutest (40-45 μm) of these species. A BLAST search of a partial (413 bp) 18S rRNA gene showed the highest similarity with Gyrodactylus sp. reported from Ameiurus nebulosus (Siluriformes) in Ontario.