Repository logo

The effects of pathogens on club cell investment in fathead minnows, Pimephales promelas



Journal Title

Journal ISSN

Volume Title




Degree Level



Fish skin is a metabolically active tissue that responds quickly to stressors and is the first line of defence against physical damage. Club cells, characteristic components of Ostariophysian fish skin, release their contents into the surrounding water upon rupture (e.g. during predation). These chemical cues act as public information of predation risk. Despite the assumption that club cells evolved under the selective force of predation, studies demonstrated that predation has no effect on club cell investment. Rather, club cell production is stimulated by skin penetrating pathogens and parasites. The experiments in this thesis investigate the responses of fish skin to manipulated pathogen risk. In the first experiment, fathead minnows (Pimephales promelas) were exposed to varying infective risk from two pathogen species that differ in pathogenicity, Saprolegnia ferax and S. parasitica. Although there was no difference in club cell density between fish exposed to the two Saprolegnia species, fish exposed to high concentrations of the pathogens had smaller club cells than those exposed to low concentrations. These results are the first to demonstrate a pathogen effect on the size of club cells. The second experiment investigated whether the physical presence of the pathogen was necessary for an alteration in epidermal parameters or whether Saprolegnia parastitica conditioned water was the only stimulus necessary to evoke a change. Results indicated a lack of treatment effect on club cell density, club cell size or epidermal thickness. The third experiment investigated the timing of club cell changes following a pathogen challenge. Although fish exposed to the Saprolegnia ferax treatment had higher club cell density than fish exposed to the control, there was no difference in club cell density between fish sacrificed on day 3, 6, 9 or 12. A portion of the test population for the third experiment was infected with black spot disease. When analyzed separately, trematode infected fish had smaller club cells than those that were uninfected. In light of inconsistent epidermal responses to pathogen challenges, and comparison with other studies, assessment of environmental stressors and population differences that may affect experimental outcomes and potentially interact with infectious agents is advised.



Pimephales promelas, fathead minnow, oomycete, Saprolegnia, club cell, epidermis, fish



Master of Science (M.Sc.)






Part Of