Search

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.

Young-of-the-year (YOY) brook trout (Salvelinus fontinalis) were collected at 2 wk intervals (15 April to 4 June 2012) after emergence from redds and occurrence of the ectoparasite Gyrodactylus colemanensis (Monogenea) recorded. Emergent YOY were not infected. Infected trout (14%) first appeared 15 May, with host age estimated to be 4 wk or less post-emergence. Prevalence and intensity increased over the study period and reached, respectively, 93% and 8.2 ± 6.1 by 4 June. Prevalence and intensity of infection was also determined for older cohorts (1+, >1+) on 6 June, with G. colemanensis occurring on representatives of all age groups. The number of hosts in each age group was estimated by mark/recapture electrofishing over a 100 m reach of the stream. Combining estimated host numbers by age group with parasite prevalence and intensity data from those groups allowed calculation of parasite total standing crop. The results indicate that, by late spring, the new host recruits already carried 64% of the parasite population in the stream, serving to illustrate the remarkable efficiency of transmission by this viviparous monogenean in a temperate stream system.