Taxonomy, Systematics, and Histopathology of Myxozoan (Cnidaria: Myxozoa) Parasites of Fishes

Abstract

Myxozoans, a parasitic lineage of cnidarians, comprise over 2500 species infecting primarily freshwater, marine, and estuarine fishes. This includes several demonstrable pathogens to cultured fishes including: Myxobolus cerebralis, the causative agent of whirling disease, Tetracapsuloides bryosalmonae, the causative agent of proliferative kidney disease, and Henneguya ictaluri, the causative agent proliferative gill disease. Muscle infecting species can reduce the value of wild caught fishes by appearance as white cysts in muscle, reducing marketability, or in the case of some Kudoa species inducing myoliquefaction, commonly referred to as pudding flesh, rendering fish valueless. Myxozoans have complex life cycles with invertebrate definitive hosts (wherein the parasite matures) and fish intermediate hosts (wherein asexual reproduction occurs). In this dissertation five species of Myxobolidae and one species of Ellipsomyxa Køie, 2003 (Bivalvulida) are described, the range for Myxobolus neurofontinalis Ksepka and Bullard, 2019 (Bivalvulida: Myxoboidae) is extended, and an alternate definitive host for Myxobolus cerebralis Hofer, 1903, the causative agent of salmonid whirling disease, is reported in the southeast US. I use genetic sequencing (PCR; small subunit ribosomal DNA [18S]) to report alternate definitive hosts for M. cerebralis in the southeast US, comprising the first report of a definitive host for M. cerebralis other than Tubifex tubifex (Muller) (Tubificida: Tubificidae). I use morphology, histology, genetic sequencing (PCR; small subunit ribosomal DNA [18S]), and phylogenetic analysis to characterize six new myxozoan species assigned to three genera. Myxobolus branchiofilum n. sp. and Myxobolus branchiopectin n. sp. from the gill filaments and rakers, respectively, of black redhorse, Moxostoma duquesnei (Leseur) (Cypriniformes: Catostomidae) from North Carolina, comprising the first myxozoans reported to infect black redhorse. Myxobolus intralamina n. sp. and Myxobolus infrabractea n. sp. from the gill and scales, respectively, of smallmouth bass, Micropterus dolomieu (Lacepede) (Centrachiformes: Centrarchidae) from North Carolina, comprising fourth and fifth Myxobolus reported to infect smallmouth bass and the first reported from smallmouth bass in the southeast US. Henneguya albomaculata n. sp. from the submucosa of the intestine and pyloric ceca of red drum, Sciaenops ocellatus (Linnaeus) (Bivalvulida: Myxobolidae) from coastal Alabama, comprising the second species of Henneguya reported to infect red drum. Ellipsomyxa intravesica n. sp. (Bivalvulida) from the gall bladder of Pangasisus macronema (Bleeker) (Siluriformes: Pangasiidae) from Vietnam, comprising the fourth species of Ellipsomyxa reported from a catfish and the first from a freshwater fish in southeast Asia. Further, I use morphology, histology, and genetic sequencing to extend the range of M. neurofontinalis to anadromous brook trout in Prince Edward Island, Canada, comprising the first report of this speciesoutside of North Carolina and the first report from anadromous brook trout. This work has resulted manuscripts published or accepted at Systematic Parasitology, Journal of Aquatic Animal Health, Journal of Parasitology, Parasitology International, and Diseases of Aquatic Organisms.