SREL Reprint #0490




Relationship Between Thermal Loading and Parasitism in the Mosquitofish

John M. Aho, J. Whitfield Gibbons, and Gerald W. Esch



The relationship between thermal loading and parasitism was examined in 980 mosquitofish, Gambusia affinis, taken from areas of varying thermal conditions at the Savannah River Plant (SRP) near Aiken, S.C.  Collections were made at 2-week intervals from May to August 1974 and again from January to February 1975.  The metacercaria of two Strigeid trematodes, Ornithodiplostomum ptychocheilus and Diplostomum scheuringi were the only species of parasites recovered.  Ornithodiplostomum ptychocheilus was always found encysted in the brain and eyes, whereas D. scheuringi was restricted exclusively to the body cavity.  The density of the body-cavity parasite was highest in fish from areas of ambient temperatures and declined in fish from areas with higher water temperatures.  The density of the brain parasite, on the other hand, was higher in fish from areas directly receiving thermal effluent than in fish from ambient-temperature areas.  The body-cavity parasite was absent from mosquitofish from Pond C, but the infection percentages were relatively consistent in fish from other areas in the Par Pond system regardless of water temperature.  The brain metacercaria were recovered from 95% of fish from Pond C.  There were higher infection percentages of brain parasites in fish from thermally altered areas of Par Pond than in those from other parts of the Par Pond system.  Three different hypotheses can be formulated to account for the relationship between thermal loading and the observed abundance and distribution patterns for these two species of parasites:  (1) a direct differential influence of temperature on the physiological tolerance of the various life-cycle stages of the parasite; (2) a direct differential impact of temperature on the distribution of the molluscs that serve as the first intermediate hosts; and (3) an effect of temperature on the abundance and distribution of the potential definitive hosts within the study area.

Keywords: Par Pond Reservoir System


SREL Reprint #0490

Aho, J.M., J.W. Gibbons, and G.W. Esch. 1976. Relationship between thermal loading and parasitism in the mosquitofish. p. 213-218. In Thermal Ecology II, edited by G.W. Esch and R.W. McFarlane. CONF 750425. ERDA Symposium Series.

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