The California roach, Hesperoleucus symmetricus, is a cyprinid fish native to western North America and abundant in the intermittent streams throughout central California. It is the sole member of its genus.
This fish is of a relatively chunky body shape, with a largish head and large eyes, but a small mouth oriented downwards. Color is a darker grayish-bluish above, and a dull silver underneath. During the breeding season, red-orange patches appear on the chin, operculum, and at the bases of pectoral, pelvic, and anal fins. The smallish dorsal fin has 7-10 rays, while the anal fin has 6-9 rays. They never get large, the maximum known being about 11 cm.
Mainly a bottom feeder, filamentous algae is the main part of its diet, followed by aquatic insects and crustaceans. It will also opportunistically eat insects and crustaceans at the surface. In turn, it is eaten by other fish, in particular green sunfish.
Spawning occurs mainly from March through June. They move into shallow, flowing water, over bottoms covered with small rocks, and form up into schools. Females lay a few eggs at a time, eventually putting down from 250 to 900 eggs each. The adhesive eggs are laid in crevices, where they stick to the rocks, and then the males fertilize them. The fry continue to dwell in the crevices until they are strong enough to swim actively.
California roaches seem to be a resilient species that takes advantage of the intermittent waters of central California under conditions too difficult for other fishes. As the springtime streams dry up in summer, roaches accumulate in large number in pools, which may be alkaline, hot (up to 95 degree Fahrenheit), and low in oxygen. They also seem to cope well with sewage-polluted waters.
Mainly found in the Sacramento River/San Joaquin River drainage, including Pit River and Goose Lake, they are known from many of the small coastal streams (Russian River, Pajaro River, Salinas River, etc). Populations in southern California and in Warner Valley, Oregon, may be introductions.