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McNeish, who has examined the fish carcasses since late August, has identified non-native species including bass, sunfish, bullhead catfish and mosquitofish.

Everywhere the mosquitofish has been introduced, the topminnow has disappeared.

The mosquitofish is not a fussy creature: It can live in filthy bodies of water and has an undiscerning appetite.

Other fish, such as the banded killifish and the mosquitofish, have expanded their range in the Potomac, also probably an indicator of climate change.

Ryan Amick and his colleagues at the Greater Los Angeles County Vector Control District are fighting the explosion of mosquitoes in Los Angeles this summer with mosquitofish.