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Experimental biological control of a trematode parasite of bluegill

Authors
Journal
Experimental Parasitology
0014-4894
Publisher
Elsevier
Publication Date
Volume
17
Issue
3
Identifiers
DOI: 10.1016/0014-4894(65)90073-1

Abstract

Abstract An investigation was begun July 1, 1962, to determine the potential of snails infected with cercariae of Posthodiplostomum minimum to produce infection in bluegills, Lepomis macrochirus. Infected snails, in aluminum wire baskets, were stocked in plastic-lined pools at rates of 1 or 5 per pool. Bluegills of 2 sizes, 1 inch or 3 inches, were stocked in the pools. All bluegills were exposed to cercariae for 24 days at which time the exposure phase of the experiment was terminated. One month later counts were made of the parasites found in each fish. One-inch bluegills contained an average of 20 parasites per fish when exposed to cercariae from 1 infected snail and 37 parasites per fish when exposed to cercariae from 5 infected snails. Three-inch bluegills contained an average of 110 parasites per fish when exposed to cercariae from 1 infected snail and 200 parasites per fish when exposed to cercariae from 5 infected snails. Comparison of treatment means revealed that the intensity of infection was related more to size of the fish than to the number of infected snails to which the bluegills were exposed. An investigation was begun October 10, 1962, to determine the effectiveness of the redear sunfish, L. microlophus, in reducing infection of P. minimum in bluegills through destruction of the snail host by the redear. Infected snails were released in pools at rates of 1, 5, or 10 per pool. Parasite-free snails were also stocked in all of the pools so that each pool contained a combined total of 100 snails. Bluegills were stocked in all of the pools. Some pools were stocked with redear, whereas others received no redear and were held as controls. Half of the pools stocked with redear contained vegetation. All bluegills were exposed to cercariae for 37 days at which time the exposure part of the experiment was terminated. One month later counts were made of the parasites found in each fish. When stocked alone with 1, 5, or 10 infected snails, bluegills averaged 48, 83, and 114 parasites per fish, respectively. In pools stocked with redear, bluegills contained an average of 16, 16, and 48 parasites per fish. In the presence of redear and vegetation, bluegills contained an average of 7, 9, and 32 parasites. Comparison of treatment means revealed that the redear was effective in significantly reducing infection of P. minimum in bluegills, and that the presence of aquatic vegetation did not reduce effectiveness of the redear.

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