While specimens in the Sacramento River may get to 1250 mm, they would not be expected to exceed 500 mm in smaller streams except in the lower reaches of tributaries where large fish migrate in for spawning in March. According to the literature, juveniles feed on invertebrates while individuals over 250 mm prefer small fish. Personal observations agree with this except that adults in small streams seem to feed as much on insects as fish. Squawfish also do not become sexually mature until their fourth year. It does well in lower elevation permanent parts of local streams including sections which dwindle to seasonal pools, but seems unable to coexist with the introduced smallmouth bass.
Roaches are usually the most abundant fish in the middle zones of local creeks.
They feed on invertebrates and filamentous algae. The Sacramento sucker is a component of almost all local streams. Suckers use their specialized mouths to scrape epilithon and associated aquatic insects from the substratum. Like the hardhead and squawfish, suckers usually don't spawn until four years old. The green sunfish, introduced from the Mississippi drainage, has become a common component of California Central Valley streams with intermittent pools, often to the detriment of native fish which it out-competes or eats.