Ecology and Evolution of Fish Blood Flukes (Digenea: Aporocotylidae)

Date of Award


Degree Type


Degree Name

Doctor of Philosophy (PhD)


Coastal Sciences, Gulf Coast Research Laboratory

First Advisor

Robin M. Overstreet

Advisor Department

Coastal Sciences, Gulf Coast Research Laboratory


Fish blood flukes (Digenea: Aporocotylidae) comprise an ancient and taxonomically diverse group of flukes that infect an array of distantly-related, non-tetrapod craniate lineages. The foundation of this dissertation comprises dissections of >2,500 fish of >200 species in 122 genera, 67 families, and 20 orders from marine and estuarine systems in the Northwestern and Eastern Atlantic Ocean, Eastern and Western Pacific Ocean, Sea of Cortez, Gulf of Mexico, Caribbean Sea, and Mediterranean Sea as well as from lakes and rivers in North America, South America, and Africa. An overview of the biological interactions between digeneans and their fish hosts indicates that digeneans exhibit marked phylogenetic and ecological specificity to particular hosts and that those host-parasite relationships have matured along a geologic timescale. Aporocotylidae is identified as a suitable group within which to study parasite-host evolution because of the phylogenetic diversity of their hosts and because of their basal position in Trematoda. I provide an updated diagnosis for Aporocotylidae, emend each generic diagnosis, confirm the generic identity of each accepted species, describe 12 new species and propose 9 new genera, and establish the host and geographic range for species and genera by identifying dubious host records and applying correct taxonomic names to each reported host species. This work culminates in the first clade-based phylogenetic hypothesis for Aporocotylidae. A strict consensus of the 22 most parsimonious trees generated from an analysis of 204 unordered, unweighted morphological characters and 36 taxa yielded a tree topology in which the fish blood flukes can be divided into "blood flukes of..." chimaeras + sharks, basal actinopterygiians + elopomorphs, otophysans, and euteleosts. Parsimony analysis of the 18S small subunit ribosomal DNA produced a single most parsimonious tree that supported the morphology-based tree topology. The analyses together suggest that (1) phylogenetic host specificity among aporocotylids is structured at the level of higher order craniate subdivisions, (2) primitive vertebrate lineages harbor primitive aporocotylids, (3) highly-derived aporocotylids infect Euteleostei, (4) most basal aporocotylids infect freshwater fishes, and (5) host switching events involve euryhaline fishes acquiring freshwater blood flukes.