Hardhead are mainly bottom feeders, foraging on invertebrates and aquatic plant material from the stream bed although they will also eat drifting insects and algae from higher in the water column. They will infrequently consume plankton and insects taken from the surface and in
Shasta Reservoir the fish found there were observed to feed on
cladocerans. They can attain in
standard length after a year and by the end of the second year lengths of and by the end of their third year. In the
American River hardheads can reach by the age of four but in the Pit River and the
Feather River fish only reach this size at age 5 or 6. Hardheads from the Feather River which had grown to were aged at 9–10 years old, and it is considered that older and larger fish may occur in the Sacramento River. Hardhead found in smaller streams rarely reach longer than while old records suggest that this species attained total lengths of up to . Hardhead reach sexual maturity after their second year and spawn in April and May when the adults migrate upstream into the smaller tributary streams. Females have been found with mature eggs in March and specimens of both sexes examined in July and August had spent
gonads. It has been estimated that the spawning occurs at different times based on location, with juvenile recruitment suggesting that hardhead spawn by May–June in the streams of the
Central Valley but at higher altitudes it may extend into August, for example in foothill streams. The adults may migrate more than from larger rivers and reservoirs may to spawn in smaller tributary streams while fish from in smaller waters will migrate short distances, either upstream or downstream, from their home pool to breed, seldom more than from their home pool. Although the spawning of hardheads in the wild has never been observed it is thought that it is probably similar to the spawning of the closely related
Lavinia exilicauda and
Sacramento pikeminnow, both species which lay their fertilized eggs in sand or gravel substrates in well oxygenated water such as riffles, rills, or faster flows at upper ends of pools. The breeding success of hardhead appears to be highest when the highest flows of a river occur between April and June. The females are very fecund and can produce over 20,000 eggs but the egg load can vary from 7,100 to 23,900 eggs. The eggs seem to mature after a full year as ovaries can contain both mature and undeveloped eggs. It is thought that the fertilised eggs develop among the gravel and that the larval and post-larval fry probably prefer the edges of streams where they can find thick vegetation to provide cover. As the young fish grow they move into deeper waters and where the streams they were hatched in are intermittent they can be swept down to the stream mouth by the current. Small juveniles of in standard length may form in large schools in shallow backwaters and among cobbles and boulders near stream banks. Adult hardhead normally occur in schools in the deepest part of pools, where the slowly cruise around during the day, becoming more active in early morning and evening when they feed. In some reservoirs large adults have been observed sitting close to the surface on warm summer days which makes the vulnerable to predation bt large fish-eating birds such as the
Western osprey and the
bald eagle. They are predominantly bottom feeders, consuming invertebrates and aquatic plants from stream beds although they will also feed on insects and algae drifting higher in the water column. They will infrequently take plankton and surface insects and, in
Shasta Reservoir they were recorded feeding on
cladocerans. Hardheads of less than mainly prey on benthic invertebrates, in particular the larvae of
mayflies and
caddis flies, as well as small snails. Larger fish grazed on filamentous algae, as well as preying on crayfish and other large invertebrates. As the fish mature their tooth structure changes; the juveniles have hooked teeth for catching insects and as they mature they develop more
molar-like crushing teeth better adapted to grind plant material and larger invertebrates. They do not appear to eat other fish. ==Conservation==