A new host and reproduction at a small size for the "snapper-choking isopod" Cymothoa excisa (Isopoda: Cymothoidae)

Abstract

Cymothoa excisa Perty, 1833 (Isopoda: Cymothoidae), the "snapper-choking isopod," is a fish parasite previously known from fifteen host species; it ranges along the Atlantic coast from Brazil to Massachusetts. However, no host information has previously been published for the species north of the Gulf of Mexico. We encountered this isopod in 3.0% (12/399) of weakfish (Cynoscion regalis) collected at St. Catherines Island, Georgia. This is the first report of weakfish as a host for C. excisa. We confirmed our morphological identifications by sequencing a fragment of the mitochondrial cytochrome oxidase I (COI) gene from our specimens and a previously identified C. excisa specimen from the Gulf of Mexico. Three C. excisa (body lengths 13-15 mm) were ovigerous with brood sizes ranging from 171 to 483 embryos. These represent some of the smallest ovigerous C. excisa known and the smallest brood sizes reported for the species. Due to morphological changes during development, the identification of immature cymothoid isopods is challenging. The COI sequences we report will facilitate identifying all life stages of this species in the future.