FISH PARASITOLOGY - SHORT COMMUNICATION Supplemental diagnosis of Gyrodactylus nebulosus Kritsky and Mizelle, 1968 (Monogenea) on 0+ age Ameiurus nebulosus (Siluriformes) considered for commercial grow-out in Southwestern Nova Scotia, Canada Eric Leis 1 & Roland Leblanc 2 & Russell Easy 3 & Hillary Dort 3 & David Cone 4 Received: 8 May 2019 /Accepted: 29 December 2019 # Springer-Verlag GmbH Germany, part of Springer Nature 2020 Abstract Gyrodactylus nebulosus Kritsky and Mizelle, 1968 is reported for the first time from brown bullhead Ameiurus nebulosus (Siluriformes; Ictaluridae) in Nova Scotia. The study results from a screening of parasites with the potential to disrupt commercial rearing of wild-caught young-of-the-year (YOY) brown bullhead. Infected YOY were collected July 30, 2018 and estimated to be 3 weeks old. Eight of 10 fish were infected. Mean intensity was 3.1 ± 3.5 with a range of 1–10. The parasite occurred all over the body surface, but particularly on the ventral regions of the head including the base of the maxillary barbels. Diagnostically important features of the anchors, ventral bar/shield, marginal hooks, and male copulatory organ are described. A partial sequence of the 18S rRNA gene (432 bp) is included and represents the first confirmed molecular data for this species. Molecular analysis revealed a high similarity (99.3%) to a Gyrodactylus sp. reported from the same host, A. nebulosus, in Ontario and the next closest similarity (96.9%) to Gyrodactylus fairporti Van Cleave, 1921 from Ameiurus melas in Wisconsin. The report extends the known distribution of G. nebulosus from North Dakota, Iowa, and Ontario to Nova Scotia. The study concludes that any commercial venture to harvest local YOY brown bullhead from the wild for intense grow-out in captivity should include appropriate quarantine and therapeutic treatments for G. nebulosus as part of the operation. Keywords Gyrodactylus nebulosus . Brown bullhead . Ameiurus nebulosus . Nova Scotia . 18S rRNA gene . Monogenea Introduction Brown bullhead (Ameiurus nebulosus) is an important angling and commercial freshwater catfish native to rivers and lakes in central and eastern North America, from Canada to the southern USA (Scott and Crossman 1973). This fish is widespread in Nova Scotia and populations in the southwest of the province are being considered for commercial develop- ment in which wild-caught young-of-the-year (YOY) are grown out in captivity (Gilles Comeau, Saunieville Trawler Ltd., pers. communication). There is significant interest in knowing whether these wild-caught brown bullhead are in- fected with parasites that can readily reproduce in captivity and cause disease. One group of potential pathogens of fresh- water catfishes in North America is species of Gyrodactylus von Nordmann, 1832 (Monogenea) (Hoffman 1979). Three parasite species of the genus, Gyrodactylus fairporti Van Cleave, 1921, Gyrodactylus ictaluri Rogers, 1979, and Gyrodactylus nebulosus Kritsky and Mizelle, 1968, are known from freshwater catfishes in North America, all having been reported ectoparasitic on wild and captive hosts (see Leis et al. 2018). Hoffman (1979) reported significant mortality of young channel catfish ( Ictalurus punctatus ) caused by G. ictaluri at fish farms in southern USA. Leis et al. (2018) reviewed the taxonomy of the three parasite species and Section Editor: Shokoofeh Shamsi * Eric Leis eric_leis@fws.gov 1 La Crosse Fish Health Center – Midwest Fisheries Center, United States Fish and Wildlife Service, Onalaska, WI 54650, USA 2 Salmon River Salmon Association, Meteghan River, Nova Scotia B0W 2L0, Canada 3 Department of Biology, Acadia University, Wolfville, Nova Scotia B4P 2R6, Canada 4 Present address: Dayspring, Nova Scotia B4V 5R7, Canada https://doi.org/10.1007/s00436-019-06598-y Parasitology Research (2020) 119:1149–1153 Published online: 4 February 2020 /