Indirect Effects and Biological Control of Mosquitoes by Mosquitofish

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Abstract
(1) The mosquitofish, Gambusia affinis (Baird and Girard), reduced the abundance of the pest mosquito Culex tarsalis Coquillet in a rice field in San Joaquin Valley, California [U.S.A.]. (2) The mosquitofish also reduced the abundance of other aquatic invertebrate taxa, including predatory insects and zooplankton. (3) The reduction in predatory insect abundance, due to the fish, reduced mosquito mortality due to insects. (4) The reduction in the abundance of alternative prey (mainly zooplankton) increased predation rates on mosquitoes by individual fish. A low abundance of zooplankton increased the predation rates of individual predatory insects. (5) Successful control of mosquitoes results from a direct negative effect by mosquitofish that more than outweighs indirect positive effects of the mosquitofish on mosquitoes. In other studies, the introduction of mosquitofish increased the abundance of mosquito larvae; indirect positive effects of the type demonstrated in this study could account for these results.