Sometimes you have to prove the obvious to get something done. The mosquitofish is being distributed around the world to control mosquitoes--without regard for its effects on other aquatic species. New research shows that mosquitofish devour tadpoles just as readily as mosquito larvae and so can decimate native amphibians.

"Handing out exotic mosquitofish as a control of mosquitoes is an outdated government policy that needs to be changed," says Lee Kats of Pepperdine University in Malibu, California, who presents this research with Jeff Goodsell in the August issue of Conservation Biology. This is the first study to demonstrate unequivocally that mosquitofish show no preference for mosquito larvae.

Distributed by the Los Angeles County Mosquito Abatement and Vector Control Center, mosquitofish have become established in many streams in the Santa Monica Mountains within the last 15 years. Because these streams have no native fish, the amphibians that live there lack defenses against fish predation. Amphibians native to these streams include the California newt, the Pacific treefrog and the California treefrog, which is a candidate for protected status.

Previous studies have shown that mosquitofish eat amphibians such as California newt larvae in Santa Monica Mountain streams. But these studies have been criticized because the mosquitofish were not offered alternate prey, leaving them no choice but to eat newt larvae.

Kats and Goodsell addressed this criticism by offering mosquitofish both Pacific treefrog tadpoles and mosquitoes. The researchers put bottomless two-by-two-foot tubs in fishless Santa Monica Mountain streams and added two mosquitofish, 20 tadpoles and 40 (low-density) or 80 (high density) mosquito larvae. These predator and prey densities approximated those naturally found in local streams.

After six hours, the mosquitofish in the "low-density" tubs had eaten all the mosquito larvae and more than 85% of tadpoles. Similarly, t
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Contact: Lee Kats
lkats@pepperdine.edu
310-456-4310
Society for Conservation Biology
29-Jul-1999