First detection of Argulus cf. versicolor (Arthropoda: Argulidae) on the recently established and likely endangered shoal bass, Micropterus cataractae, in Georgia, USA

Argulus spp. are ectoparasitic branchiurans that parasitise freshwater fishes worldwide, yet their diversity and distribution in Georgia remain poorly documented. Shoal bass, Micropterus cataractae Williams et Burgess, is a recently established species with a restricted native range in the Apalachicola-Chattahoochee-Flint River Basin of the southeastern United States and is likely endangered. In Georgia, published records of Argulus spp. are limited to the early 1900s. In the present study, we collected a single specimen of Argulus cf. versicolor from the gills of a shoal bass in central Georgia. Morphologically, the specimen most closely conformed to Argulus versicolor Wilson, 1902. It had conspicuous darkened areas along the carapace margins, robust first antennae, five-segmented second antennae, and maxillular suckers with 48 supporting rods. Each sucker rod was composed of an elongate basal sclerite and a few shorter distal sclerites. Partial 28S rDNA and mitochondrial cytochrome c oxidase subunit I (COI) sequences were generated and compared with available sequences of congeners. In the 28S phylogeny, Argulus cf. versicolor formed a strongly supported subclade with Argulus flavescens Wilson, 1916, differing by only 0.3% at this locus; no COI sequence is available for A. flavescens. In the COI phylogeny, our specimen formed a strongly supported subclade with Argulus yucatanus Poly, 2005 and an unidentified Argulus sp. from Mexico. Argulus yucatanus showed the lowest COI divergence from our specimen at 8.6%; no 28S sequence is available for this species. Our study represents the first documented record of an argulid from shoal bass and the first record of Argulus from Georgia supported by DNA sequence data.