Mylopharodon conocephalus

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General Information
Common Name: 

Conservation Status in California: Class 3, Near threatened (Moyle et al. 2011).
Most populations are small, isolated, and are likely declining with limited information on status.

Life History: 

Life History: Stream-dwelling juvenile ( Hardhead are primarily bottom feeders that forage on invertebrates and aquatic plant material from stream substrates but they will also consume drifting insects and algae from the water column (Alley 1977). Occasionally they will feed on plankton and surface insects and in Shasta Reservoir they were known to feed on cladocerans (Wales 1946). Smaller fish ( Hardhead reach 7-8 cm SL by their first year, 10-12 cm by the end year 2 and 16-17 cm by the end of year 3 (Reeves 1964, Moyle et al. 1983, PG&E 1985, Grant 1992). They can reach 30 cm SL by age 4 (Reeves 1964) in the American River but only reach this size at age 5 or 6 in the Pit and Feather Rivers (Moyle et al. 1983, PG&E 1985). Large (44-46 cm SL) hardhead from the Feather River were found to be 9-10 years, but older and larger fish probably exist in the Sacramento River. In smaller streams, hardhead rarely grow beyond 28 cm SL (Grant 1992). Old records suggest that hardhead reach up to 1 m TL (Jordan and Evermann 1896).
Hardhead mature following their second year and spawn in the spring, mainly in April and May (Reeves 1964, Grant and Maslin 1997), judging by the upstream migrations of adults into smaller tributary streams during this time of the year (Wales 1946, Murphy 1947, Bell and Kimsey 1955, Rowley 1955). Shapovalov (1932) reported presence of mature eggs in females during March, but gonads of males and females caught in July and August were spent (Reeves 1964). Estimates based on juvenile recruitment suggest that hardhead spawn by May-June in Central Valley streams and that the spawning season may extend into August in the foothill streams of the Sacramento-San Joaquin drainage (Wang 1986). Spawning adults from larger rivers and reservoirs may migrate more than 75 km in April and May to spawn in tributary streams (Wales 1946, Moyle et al. 1995). In contrast, hardhead in small streams only migrate a short distance upstream or downstream of their home pool for spawning (Grant and Maslin 1997). In Pine Creek (Tehama County), spawning adults aggregate in nearby pools, and return to home pools after spawning (Grant and Maslin 1999). Hardhead spawning has not been directly observed; however, it is likely similar to that of hitch and pikeminnow, which deposit their fertilized eggs in sand or gravel in riffles, runs, or heads of pools (Wang 1986; Moyle 2002). Spawning success of hardhead in the lower Tuolumne River is highest when there are higher flows during in April and May (Brown and Ford 2002).
Females are highly fecund, producing over 20,000 eggs (Burns 1966). Fecundity ranged from 7,100 to 23,900 eggs in females from Pine Creek and the American River (Grant and Maslin 1999, Reeves 1964). The ovaries contain both developed and undeveloped eggs, suggesting that eggs mature after a full year (Grant and Maslin 1997, 1999). Fertilized eggs presumably develop in the interstices of the gravel until hatching. Larvae and postlarvae most likely move into stream margins with abundant cover (Wang 1986). They move into deeper habitats as they grow larger. Young from intermittent streams are swept downstream into areas of low velocity near the mouths of main rivers (Moyle 2002). In Deer Creek (Tehama County), small juveniles (2-5 cm SL) congregate in large schools in shallow backwaters. Small juveniles in the Kern River congregate among large substrates (cobble and boulders) along the stream margin (L. Brown, USGS, pers. comm. 1999).
Hardhead host a variety of parasites. Hardhead from the North Fork Feather River, Plumas and Butte Counties, were infected with an average of three parasites, including nematodes and trematodes (Alvarez 2008).

Habitat Requirements: 

Habitat Requirements: Hardhead are often found at low to midelevations in relatively undisturbed habitats of larger streams (Moyle and Daniels 1982, Mayden et al. 1991), with high water quality (clear, cool). In the Sacramento River, however, they are common in both the mainstem and tributaries up to 1500 m (Reeves 1964). Summer temperatures in rivers were they are common reach 20?C, below optimal temperatures (24-28?) determined by laboratory experiments (Knight 1985). In a thermal plume in the Pit River, hardhead preferred the warmest temperatures available (17-21?C; Baltz et al. 1987). Similarly, hardhead acclimated to 12, 15, and 18 °C water preferred water 19.6 to 20 °C and avoided water temperatures less than 17 °C in a laboratory setting (Cocherell et al. 2007). However, lower temperatures appear to increase swimming performance. Hardhead swimming performance was higher at 15 °C than at 10 or 20 °C (Myrick and Cech, Jr. 2000). Their distribution may be limited to well-oxygenated streams and reservoir surface waters by low oxygen levels at warm temperatures (Cech et al. 1990). They prefer pools and runs with deep (>80 cm) clear water, slow (20-40 cm/sec) velocities and sand-gravel-boulder substrates (Alley 1977, Cooper 1983, Knight 1985, Moyle and Baltz 1985, Mayden et al. 1991). May and Brown (2002) describe water quality and habitat variables associated with a foothill group of mostly native fishes, including hardhead (Table 1). Adults mostly occupy the lower half of the water column in streams (Knight 1985, Moyle and Baltz 1985) but may stay close to the surface in reservoirs (Hunt et al. 1988, Vondracek et al. 1988). They are often found alongside Sacramento pikeminnow and Sacramento sucker. They are usually absent from streams occupied by alien species, especially centrarchids (Moyle and Daniels 1982, Mayden et al. 1991, Moyle et al. 2002), and streams that have been heavily altered (Baltz and Moyle 1993). Because they are poor swimmers, they may also be absent from stream reaches above barriers, even if there are ladders that allow salmonid passage (Myrick 1996, Myrick and Cech, Jr. 2000).
Hardhead populations are well established in mid-elevation reservoirs used exclusively for hydroelectric power generation, such as Redinger and Kerkhoff Reservoirs on the San Joaquin River, Fresno County, and Britton Reservoir on the Pit River, Shasta County. In the Pit River, hardhead are most abundant in Upper Britton Reservoir where habitat is more riverine and less abundant in the lacustrine habitat of the lower reservoir, where alien centrarchids, particularly predatory basses, are more abundant (PG&E 1985, Vondracek et al. 1988).


Distribution: Hardhead are widely distributed in streams at low to mid elevations in the Sacramento-San Joaquin and Russian River drainages (Leidy 1984, Moyle 2002). Their range extends from the Pit River (south of the Goose Lake drainage), Modoc County, in the north to the Kern River, Kern County, in the south (Moyle and Daniels 1982, Cooper 1983). In the San Joaquin drainage, scattered hardhead populations are found in tributary streams, but only rarely in the valley reaches of the San Joaquin River (Moyle and Nichols 1973, Saiki 1984, Brown and Moyle 1987). Jones and Stokes (1987) found a very small number of hardhead during an extensive sampling program of the lower Kings and San Joaquin rivers, indicating that hardhead have opportunities to recolonize historic habitats but fail to do so, due to dewatering and other factors. They are absent from the Cosumnes River. In the Sacramento River drainage, hardhead are found in most large tributaries as well as in the Sacramento River (Moyle 2002). In the South Yuba River, they make up 55% of the fish caught in the lower 15 km (Gard 2002). They are present in the Russian River and in the Napa River, although the Napa River population is very restricted in its distribution (R. Leidy, USEPA, pers. comm.). They are widely, if spottily, distributed in the Pit River drainage (Cooper 1982, Moyle and Daniels 1982), including the main Pit River and its series of hydroelectric reservoirs. Although their current status is uncertain, hardhead apparently also once occurred in Alameda and Coyote Creeks (Leidy 2007). They are present in the northern coast range in the larger tributaries to the Sacramento River such as Cache Creek, Putah Creek, and Clear Creek, mainly in canyon reaches with deep pools.

Abundance Trends: 

Trends in Abundance: Historically, hardhead were regarded as widespread and locally abundant (Ayres 1855, Jordan and Evermann 1896, Evermann 1905, Rutter 1908, Follett 1937, Murphy 1947, Soule 1951, Reeves 1964). Hardhead are still fairly widespread in the foothill streams (May and Brown 2002), but their specialized habitat requirements, combined with widespread alteration of downstream habitats, has resulted in most populations being localized and isolated (Moyle 2002). This makes them vulnerable to localized extinctions. Consequently, hardhead are much less abundant than they were, especially in the southern half of their range (Moyle 2002). Historical records noted their presence in most foothill streams in the San Joaquin drainage (Reeves 1964), but Moyle and Nichols (1973) found them in only 9% of the streams sampled. Brown and Moyle (1987, 1993) subsequently resampled most of the same sites and found that a number of populations had disappeared during the 15-year period. Ford and Brown (2001) found they were uncommon in the lower Tuolumne River and largely confined to a cool-water reach about 30 km long, associating mainly with other native fishes. In the Cosumnes River, hardhead are absent, despite a fairly natural flow regime, apparently because of the invasion of redeye bass (Micropterus coosae). They are still common in the mainstem Sacramento River, lower American and Feather Rivers, some smaller streams (e.g., Deer, Pine, Clear Creeks), and reaches upstream of foothill reservoirs (Moyle 2002). They are very rare in the Napa River (Leidy 1984 and pers. comm.) and uncommon in the Russian River (Moyle 2002). In the Pit River, they have a discontinuous distribution and are limited to canyon reaches and hydroelectric reservoirs (Moyle and Daniels 1982, Herbold and Moyle 1986).
Hardhead were once abundant enough in reservoirs to be regarded as a problem species, under the assumption they competed for food with game fishes such as trout (Moyle 2002). Most populations likely resulted from colonization by juveniles before introduced predators became abundant and largely extirpated hardhead from reservoirs. Populations declined dramatically within two years in Shasta Reservoir, Shasta County (Reeves 1964), leaving only a small number to persist (J. M. Hayes, CDFG, pers. comm.). Crashes of large populations in reservoirs similarly were reported from: Pardee Reservoir on the Mokelumne River, Amador/Calaveras County (Kimsey et al. 1956); Millerton Reservoir on the San Joaquin River, Fresno County (Bell and Kimsey 1955); Berryessa Reservoir, Napa County (Moyle 1976); Don Pedro Reservoir, Tuolumne County; and Folsom Reservoir, El Dorado County (Kimsey et al. 1956). Currently, they are largely absent from reservoirs that undergo strong annual variations in water level, although they can survive in hydroelectric reservoirs where water level fluctuation are less, such as Britton Reservoir on the Pit River and Redinger Reservoir on the San Joaquin River (Moyle 2002).


Description: Hardhead are large cyprinids, reaching lengths in excess of 60 cm SL. The body shape is similar to that of Sacramento pikeminnow (Ptychocheilus grandis), with which they co-occur, but the body is deeper and heavier and the head is less pointed. Hardhead also differ from pikeminnow in that their maxilla does not extend beyond the anterior margin of the eye and they possess a bridge of skin (frenum) connecting the premaxilla to the head. Hardhead have 8 dorsal rays, 8-9 anal rays, and 69-81 lateral line scales. Adults have large molariform pharyngeal teeth, but juvenile teeth are hook-like. Juveniles are silver; adults are brown-bronze dorsally. During the spawning season, adult males develop small white nuptial tubercles on the head and along a band that extends from the head to the base of the caudal fin (Moyle 1976). Prolarvae and early postlarvae have scattered caudal pigmentation and two distinct dark spots, one above flexion, one at ventral base of caudal peduncle (Wang and Reyes 2007). Some midventral pigmentation may also occur. Early juveniles have small mouths (maxilla ends in front of eye), high myomere counts (46-50), and enlarged nostril flaps.