Perkins, D., J.W. Heckel IV, B. High & E.J. Billman. (2023). First documentation of Ergasilus centrarchidarum on Smallmouth Bass in Idaho. Western North American Naturalist. 83(2):283-288.

480945

10.3398/064.083.0214 [view]

Perkins, D., J.W. Heckel IV, B. High & E.J. Billman

2023

83(2):283-288.

Publication

Ergasilus centrarchidarum is a parasitic copepod that infects the gills of fishes in the family Centrarchidae. This parasite has been introduced in many regions of North America through introduction of infected Smallmouth Bass (Micropterus dolomieu); however, effects of E. centrarchidarum on its hosts have been poorly studied. Ergasilus centrarchidarum was first discovered infecting Smallmouth Bass in Ririe Reservoir in 2020, although timing of introduction remains uncertain. Our objective was to determine prevalence and intensity of infection of E. centrarchidarum on Smallmouth Bass in Ririe Reservoir. We used angling to collect Smallmouth Bass in the upstream portion of Ririe Reservoir in July 2021. On each fish, we documented presence of copepods and categorized intensity of infection in the left gill chamber (i.e., low, <10 copepods; medium, 10-20 copepods; and high, >20 copepods). Additionally, we euthanized 24 Smallmouth Bass to quantitatively determine intensity of infection. Prevalence of infection of E. centrarchidarum on Smallmouth Bass was 100% (n = 69 fish). Half of the Smallmouth Bass sampled were classified as having a high infection, while only 10% were classified with a low infection. In the lethally sampled fish, mean intensity of infection in the left gill chamber was 27 copepods (SE = 3.9). We did not observe damage to the gills of infected Smallmouth Bass. Additionally, we did not observe a relationship between relative weight and the category of intensity of infection. Therefore, we did not find evidence that E. centrarchidarum negatively influenced Smallmouth Bass in Ririe Reservoir; however, further research should directly study potential negative impacts of E. centrarchidarum on Smallmouth Bass. We did not find documentation of E. centrarchidarum elsewhere in Idaho; however, free-living Ergasilus spp. have been documented in Dworshak Reservoir, suggesting that E. centrarchidarum may be found in other waterbodies in Idaho.

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