Cotylogaster occidentalis (Aspidogastrea: Aspidogastridae) from Freshwater Drum, Aplodinotus grunniens (Actinopterygii: Sciaenidae), in Northeastern Oklahoma

Freshwater Drum, Aplodinotus grunniens Rafinesque, 1819 are endemic to freshwater environs of the Americas, and their distributional range extends as far north as the Hudson Bay of Canada and reaches as far south as the Usumacinta River Basin of Guatemala (Fremling 1980). In the United States, eastward distribution includes the southern Great Lakes, eastern Appalachians and the entire Mississippi basin westward as far as Kansas, Oklahoma, and Texas (Page and Burr 2011). This fish appears to have the greatest latitudinal range of any freshwater fish in North America. It feeds mostly on small crustaceans, clams, snails, insect larvae (especially chironomids) and small fish (Miller and Robison 2004). In Oklahoma, A. grunniens occurs throughout the state, mainly in the larger lakes and rivers but uncommon to absent in the northwest (Miller and Robison 2004). Freshwater Drum have been reported to harbor over 66 taxa of parasites, including protistans, aspidogastreans, monogeneans, trematodes, cestodes, nematodes, acanthocephalans, leeches, molluscs, and crustaceans (Hoffman 1999). One of these parasites, an aspidogastrean, Cotylogaster occidentalis Nickerson, 1902, was originally described from A. grunniens in the Minnesota River, Minnesota (Nickerson 1902). To our knowledge, C. occidentalis has also been reported from A. grunniens from Iowa, Louisiana, Mississippi, Tennessee, and Lake Erie, Canada (Simer 1929; Bangham and Venard 1942; Sogandares-Bernal 1955; Dechtiar 1972; Stromberg 1970; Hoffman 1999), and from freshwater mussels from Iowa (Kelley 1927), Michigan (Fredericksen 1972), North Dakota and Manitoba, Canada (Carney 2015). In addition, a report by Huehner and Etges (1972) describing Cotylogasteriodes barrowi from freshwater mussels (Lampsilis spp.) from Ohio was found to represent an immature stage of C. occidentalis by Fredricksen (1972). The life cycle of C. occidentalis normally takes place in snails but can also involve fishes, including experimental infections of A. grunniens (Dickerman 1948). Nothing is known about C. occidentalis in Oklahoma. Here we present data on specimens of C. occidentalis obtained from 1 individual A. grunniens from the state, including new information on the parasite from scanning electron microscopy.