A New Myxobolus (Cnidaria: Myxosporea: Myxobolidae) from the Gill Arch of the Western Creek Chubsucker, Erimyzon claviformis (Cypriniformes: Catostomidae), in Arkansas, USA.

Purpose: No myxosporean species has been fully described from the gill of the western creek chubsucker, Erimyzon claviformis (Girard, 1856). Here, we report from morphometric, histopathological, and DNA sequence data on a new species of Myxobolus Bütschli, 1882 from the gill arch of E. claviformis from the Red River drainage, Arkansas, USA.

Methods: Between June 2021 and September 2022, 49 E. claviformis were taken with a backpack electrofisher from various watersheds in Calhoun, Columbia, Polk, and Sevier counties, Arkansas, USA, and McCurtain County, Oklahoma, USA, and their gills were examined macroscopically for myxozoan parasites. Gill samples with visible plasmodia were placed in individual vials containing 10% neutral-buffered formalin and 95% molecular grade ethanol. Morphometric analysis and photographic documentation was performed on plasmodia and released myxospores. SSU rRNA gene sequencing was performed on free myxospores, and intact gill tissue was evaluated for associated histopathologic changes.

Results: Two of seven (29%) E. claviformis from Sevier County, Arkansas, were found to harbor plasmodia on the gill arches which yielded myxospores of a new species of Myxobolus. Myxospores of Myxobolus girardi n. sp. were orbicular to broadly elliptoid, with two ovoid to pyriform polar capsules. Two previous myxozoans found on gill lamellae reported only as Myxobolus sp. "A" and "B" and the new species can readily be distinguished from both of them by size and shape. Myxobolus girardi n. sp. was found to be most genetically similar (99.3%) to Myxobolus stuartae McAllister, Cloutman, Camus, Trauth, Ray, Robison, and Whipps, 2022 which infects the fins of E. claviformis, but at percentages considered to be representative of interspecific variation for the SSU rRNA gene.

Conclusion: This is the first gill infecting myxosporean described from E. claviformis and adds to our growing knowledge of these parasites from catostomid fishes.