Scientific NameMylopharodon conocephalus
IdentificationHardhead, adult, right side. Location: Center for Aquatic Biology and Aquaculture, UC Davis. Date: 17 May 2007. Photo by Dave Giordano, Ecosite Media.Hardhead, adult. Photo courtesy of Dennis Cocherell, UC Davis.Hardhead. Location: Feather River. Date: 19 April 2010. Note the size of the mouth, which is smaller than that of a Sacramento pikeminnow. Photo by Lisa C. Thompson.Hardhead, juvenile. Photo courtesy of Dennis Cocherell, UC Davis.
- Large minnows, sometimes greater than 60 cm SL, rarely exceed 30 cm in smaller streams.
- Slightly deeper bodied than Sacramento Pikeminnow
- Less pointed snout than Sacramento Pikeminnow
- Maxilla doesn’t extend past front margin of eye, has frenum (bridge of skin) connecting upper lip to snout (Sacramento Pikeminnow lacks a frenum)
- Coloration: brown or dusky bronze back, silvery sides
- Young fish silver in color
- Breeding males may develop white tubercles along snout and laterally along body
- Fin rays: dorsal 8, anal 8-9
- Lateral line scales: 69-81
Hardhead are typically found in small to large streams in a low to mid-elevation environment. Hardhead may also inhabit lakes or reservoirs. All ages are omnivores though the juvenile and adult fish have a slightly different diet and tooth structure for feeding. In general these fish will eat benthic invertebrates, aquatic plants and algae, or insects. The young fish typically feed on mayfly and caddisfly larvae, as well as small snails. Older fish may focus on plants, crayfish, and larger invertebrates. In a lake environment the fish may also feed on zooplankton. Within a stream Hardhead tend to prefer warmer temperatures than salmonids and they are often found associated with pikeminnows and suckers. Their preferred stream temperature might easily exceed 20ºC, though these fish do not favor low dissolved oxygen levels. Therefore the Hardhead minnow is usually found in clear deep streams with a slow but present flow. Most Hardhead reach sexual maturity at 3 years and spawn in the spring around April-May, though spawning may take place as late as August. In small streams Hardhead tend to spawn near their resident pools, while fish in larger rivers or lakes often move up to 30-75 km to find suitable spawning grounds. Though spawning may occur in pools, runs, or riffles, the bedding area will typically be characterized by gravel and rocky substrate. Females usually produce 7,000-24,000 eggs per year, though some fisheries biologists believe that the eggs may take two years to develop within the female. Upon hatching, young larval Hardhead remain under vegetative cover along stream or lake margins. As the juveniles grow they may move to deeper water or be swept downstream to larger rivers below. Adult Hardhead may live up to 9 or 10 years.
Links to Other Research
Temperature Preference and Tolerance of Hardhead Minnows research project webpage.
Thompson, L.C., N.A. Fangue, J.J. Cech, Jr., D.E. Cocherell, and R.C. Kaufman. 2012. Juvenile and adult hardhead thermal tolerances and preferences: Temperature preference, critical thermal limits, active and resting metabolism, and blood-oxygen equilibria. Center for Aquatic Biology and Aquaculture Technical Report, University of California, Davis. Download