Mylopharadon conocephalus, known as the hardhead, is a freshwater ray-finned fish from the family Cyprinidae, the carps and minnows, which is endemic to California. It is the sole member of the monotypic genus Mylopharadon.
The hardhead has an elongated, slender body which is brown to dusky bronze above, the larger fish being darkest, with silver sides. The dorsal fin has its origin behind that of the pelvic fin, It has 69-81 scales on its lateral line; the dorsal fin has 8 rays. The jaws are not extendable and there is a premaxillary frenum. The snout is long and pointed, ending with the large, terminal mouth which reaches back to the front of the eye. It has 2.5-4.2 pharyngeal teeth. It grows to around 30 centimetres (12 in) standard length.[2] The juvenile fish are silvery. The adult males grow small white nuptial tubercles on the head and on a band extending from the head to the caudal peduncle in the Spring spawning season.[3]
The range of the hardhead includes much of the drainage basin of the Sacramento and San Joaquin in California, and within the range it is widely distributed in the foothill streams. The Kern River, Kern County, is the southernmost part of the range and it reaches north to the Pit River drainage in Modoc County. It is absent from the Clear Lake basin and from most of the streams draining into San Francisco Bay, other than the Napa River and Russian River, where it is not common.[1]
Hardhead habitat includes deep pools over rocky and sandy substrates in small to large rivers. It prefers relatively undisturbed conditions and normally can be found in larger streams at low and mid-elevation. It shows to preference for deep, clear pools which have substrates consisting of sand, gravel or boulders and a slow current. It occurs in some mid-elevation reservoirs but the populations in reservoirs is usually temporary as populations may grow large, then rapidly decline. It tends to be found in the lower half of the water column in rivers and streams but in slower flows or still waters, such as reservoirs, it cab be found close to surface. It is always found in association with the Sacramento pikeminnow (Ptychocheilus grandis) and normally also with the Sacramento sucker (Catostomus occidentalis occidentalis). It cannot normally be found in waters where alien species, especially sunfish, are dominant.[1]
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 7–8 centimetres (2.8–3.1 in) in standard length after a year and by the end of the second year lengths of 10–12 centimetres (3.9–4.7 in) and 16–17 centimetres (6.3–6.7 in) by the end of their third year. In the American River hardheads can reach 30 centimetres (12 in) 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 44–45 centimetres (17–18 in) 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 28 centimetres (11 in) while old records suggest that this species attained total lengths of up to 1 metre (3.3 ft).[4]