CORONA, Calif. -- Contrary to its name, the mosquito fish might not be king fish when it comes to mosquito abatement. September is the region's traditional peak in mosquito populations and West Nile virus outbreaks, and 2008 promises to be a bad year for the spread of the virus. During the past month, 23 Riverside County, Calif. residents were diagnosed with West Nile virus, and tests indicate that a lot more mosquitoes carrying the virus are out thee. It's one more reason why a team of Riverside County researchers hopes to add a new weapon to the arsenal against the spread of the mosquito-born virus. Their secret weapon? The arroyo chub, a small native fish not well-known for its predatory skills. However, researchers at UC Riverside and the Orange County Water District at the Prado Wetlands have discovered the little fish's knack for cutting into the mosquito population. Unlike the mosquito fish, an invasive and nonnative species popular with vector control districts, the chub is a natural part of the local ecosystem and can be legally introduced to open waterways where the mosquito fish are limited. Dwindling in numbers, the chub has been labeled a "species of concern" in California, and researchers are hoping that by marrying the fish to mosquito abatement, the chub could be reintroduced to local waterways. "The idea is to create a win-win situation by using the natural predator-prey system to control mosquitoes and help the native species' programs," said Bill Walton, professor of etymology at UCR. "The chub can be as effective as mosquito fish at containing mosquitoes. You just wouldn't think of chub as mosquito-eating fish because they are found in rivers, whereas mosquitoes prefer still water." Two years ago, Orange County Water District staffers built a pond at the Prado wetlands and filled it with chub. Designed as an educational showpiece and tool in promoting native species, the pond yielded a couple of interesting findings, said Bonnie Nash, the wetlands' habitat manager for the district. "The chub were thriving in the pond conditions, and we weren't really finding mosquito larvae in the water," Nash said. The findings raise questions and implications that the study will attempt to answer, said Walton, who has been hunting for mosquito abatement alternatives for 13 years. Are the chub eating the mosquito larvae or simply deterring them from laying eggs by releasing a chemical known as a kairomone? Can this chemical be reproduced or used in widespread ways to repel mosquitoes? And, can the chub survive in ponds with natural prey such as the largemouth bass? To answer these questions, Walton and a team of graduate students, including Adena Why, have set up 10 6-by-6-foot nets inside a 4-acre pond at the Prado Wetlands. Some of the enclosed "mini-ponds" will contain no chub, while the others will be stocked with varying densities of the fish and periodically tested for mosquito larvae. The experiment will test the fish's ability to control mosquitoes and to survive in the shallow, poorly oxygenated pond water, Why said. If chub, 1- to 2-inch silver fish, prove effective at mosquito abatement, they have certain advantages over the mosquito fish, she said. In a lot of ways, the arroyo chub is no match for the mosquito fish. It's not as aggressive or as hardy as the mosquito fish, which can live in an inch of warm water and reproduces rapidly, Why said. But, for those reasons, the mosquito fish is invasive -- preying upon native fish and amphibian eggs as well as vegetation. Unlike the mosquito fish, the chub wouldn't disrupt the local ecosystem, Why said. "Also, the chub are a fish that has adapted to the boom-or-bust conditions we have in the Santa Ana River, which can go from flooded to bone-dry in months," Walton said. "There are a lot of people who are interested in this study once we can get it off the ground." The study has been delayed while the researchers await blessing from officials of the Department of Fish and Game, but Walton hopes to have the ponds stocked with fish by the end of the month and results by next year. (E-mail Paige Austin at paustin(at)PE.com.)(Distributed by Scripps Howard News Service, www.scrippsnews.com.)
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