Defense Date


Document Type


Degree Type

Master of Science

Degree Name

Marine Science

First Advisor

Christopher A. Blanar, Ph.D.

Second Advisor

Lauren E. Nadler, Ph.D.

Third Advisor

Kelly L. Weinersmith, Ph.D.


Parasites, Trematode, Behavior, Intermediate Host, California Killifish, Experimental Infection


Parasites with complex life-cycles may alter their intermediate host’s phenotype to increase the chance of successful transmission to their next host. This parasite-induced host modification often occurs in the form of behavioral changes, such as increased frequency of irregular locomotor behaviors (e.g., conspicuous behaviors), particularly in systems where the parasite is transmitted trophically through a predation event. However, most empirical evidence of host behavioral modification by parasites comes from a few model host-parasite systems and are frequently studied following a stressor (e.g., simulated predator attack). One host species studied is the California killifish Fundulus parvipinnis, which is infected by the brain-infecting trematode Euhaplorchis californiensis. Here, we assess the degree of behavioral modification of a population of F. parvipinnis by E. californiensis in the absence of a visual stressor, such as a predator or a human observer. In past studies, behavior modifications that have been observed include the tendency for fish to stay close to the surface and conspicuous swimming behaviors, such as darting, surfacing, and flashing. However, in this study, infection treatment alone did not significantly alter the proportion of fish in the top compartment. Similarly, infection treatment also did not significantly affect either the total conspicuous behaviors or any of the individual conspicuous behavior that were displayed by the fish. Taken together, these findings suggest that the nature of behavior modification by E. californiensis may be context-specific (e.g., presence of a visual stressor) and influenced by life history traits (e.g., parasite maturity, age of fish upon infection, coinfection).