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Host distribution and development of Pseudodelphis oligocotti (Dracunculoidea: Nematoda), a parasite of eelgrass bed fishes

University of British Columbia

Transmission is a key point in parasitic life cycles and should be accurate for specific hosts if parasites are particular in their host requirements. Occasionally breadth of host range is correlated with mode of transmission: many parasites are chscriminatirig in their transmission and have narrow host ranges, while some with incus criminate transmission have broad host ranges, reflecting relaxed host requirements or a similarity between hosts. This thesis investigates the mode of transmission and host range of parasite Pseudodelphis oligocotti (Nematoda: Dracunculoidea) because it poses a problem: P. oligocotti infects nine fish species but only completes development in two - Apodichthysflavidus and Gobiesox meandricus. Presumably, the seven other fishes serving as unusual hosts are inappropriate for parasite development due to some physiological reason, yet the two successful host species seem very different. I propose that P. oligocotti?, mode of transmission accounts for this pattern. To deterrnine the life cycle and host range of P. oligocotti, I surveyed 24 coastal fish species from nine British Columbia localities for prevalence and intensity of infection, stages of parasite development, and their distribution in host tissues. Pseudodelphis oligocotti infects riine species of coastal marine fishes. It infects A. flavidus at the highest rate and intensity: prevalence of infection was as high as 80%, and mean intensity was as high as 19 worms per infected host at certain localities. Subadult and adult P. oligocotti occurred in the body cavity of all nine fish hosts. Larvigerous P. oligocotti were only recovered from A. flavidus and one specimen of G. meandricus, where they occurred in the hepatic sinus. Infective first-stage larvae were recovered from gills and associated tissues oi A. flavidus. Histology and scanning electron microscopy confirmed that larvae breach the gills to gain access to the external environment. I experimentally infected potential intermediate host Tigriopus californicus with larvae from larvigerous P. oligocotti, recording mortality rates due to infection and larval development. Up to 57.1% of the copepods became infected with an average 1.26 worms per infected host. Larvae developed to the third-stage (infective to fish) in 14 to 15 days at 15 - 24.4°C. Copepod mortality did not increase as a result of infection. Intermediate hosts containing third-stage larvae were fed to uninfected A., flavidus. Infections were established in two of the 10 specimens. Results demonstrate that P. oligocotti is transmitted between fishes by ingestion of infected free-living copepods. Fishes that P. oligocotti infects share habitat with A., flavidus and many ingest free-living copepods. To examine whether ecological association between hosts predicts how far P. oligocotti develops in those hosts — an indication of host suitability — I characterized fishes by their diets, microhabitats, and taxonomy from literature sources. Hosts that are more ecologically similar to A., flavidus support more advanced stages of P. oligocotti than those that are phylogenetically related. This suggests that opportunity for infection determines parasite host range.

Thesis/Dissertation

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2009-07-02

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http://hdl.handle.net/2429/9939

Zoology

University of British Columbia

UBCV

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