A Novel Gonadotropic Microsporidian Parasite (Microsporidium clinchi n. sp.) Infecting a Declining Population of Pheasantshell Mussels (Actinonaias pectorosa) (Unioinidae) from the Clinch River, USA

Freshwater mussels of the order Unionida are among most endangered animal groups globally, but causes their population decline often enigmatic, with little known about role disease. In 2018, we collected wild adult pheasantshell (Actinonaias pectorosa) and mucket ligamentina) during an epidemiologic survey investigating ongoing mussel mass mortality event in Clinch River, Virginia Tennessee, USA. Histopathology transmission electron microscopy showed a novel microsporidian parasite primarily infecting ovary pheasantshell. Sequencing small subunit rRNA gene produced 1333 bp sequence greatest similarity to Pseudonosema cristatellae (AF484694.1; 86.36%; e-value = 0), microsporidium freshwater bryozoan (Cristatella mucedo). Microsporidia were observed 65% (17/26) examined female (A. no (0/2) muckets occurred at non-mortality sites. Our findings indicate that parasite, Microsporidium clinchi n. sp., is present while likely not cause mortality, could reduce fecundity recruitment this declining threaten success reintroductions. Surveillance M. sp. evaluation broodstock progeny for microsporidia would therefore be prudent.