Hesperoleucus symmetricus

Hesperoleucus symmetricus (Baird & Girard, 1854)

California Roach

Lectotype: USNM 191, present designation. This species was originally described as Pogonichthys symmetricus by Baird & Girard (1854) from specimens collected in the San Joaquin River at Fort Miller, Fresno Co., CA. Paralectotypes: USNM 440410; ANSP 5330–33; MCZ 1961; MNHN 0000–0353.

The benchmark California Roach is based on Baird & Girard (1854). Individuals primarily occupy streams/ rivers flowing into California’s Central Valley, most of which are isolated to some degree. Groups of California Roach appear to become easily isolated from one another and adapted to local conditions, particularly following anthropomorphic changes to the landscape (Brown et al. 1992). Many of these isolated groups are distinguishable both morphologically (Brown et al. 1992) and genetically (Aguilar & Jones 2009; Baumsteiger et al. 2017). In fact, Baumsteiger et al. found every sample location of CA Roach within our study was distinctive, including support for a new subspecies and a distinct population segment (see below). Baumsteiger et al. (2017) also found California Roach from the Central Valley to be genomically distinct from those along the coast. All analyses show a clear break between these two species. Our conclusion is CA Roach sensu stricto should be limited to individuals from Central Valley drainages and the following formal description reflects this new delineation.

Description. CA Roach (H. symmetricus) are small, stout-bodied cyprinids with narrow caudal peduncles and deeply forked tails. Adult individuals usually have total lengths less than 100 mm, although fish up to 150 mm TL have been observed (Moyle 2002). The head is large and conical, with large eyes and a mouth that is slightly subterminal and slants downward. Individuals in some locations, especially those in streams of the Sierra Nevada, develop a keratinous plate on the lower jaw, referred to as a “chisel lip”. The dorsal fin is short (8–10 rays) and is positioned behind the insertion point of the pelvic fin while the anal fin is also short, with 7–9 rays (Table 1). Pharyngeal teeth (0,5,4,0) have curved tips, which overhang grinding surfaces of moderate size. CA Roach are dark on the upper half of their bodies, ranging from a shadowy gray to a steel blue, while the lower half of the body is much lighter, usually a dull white/silver color. Scales are small, numbering 47–62 along the lateral line. Individuals tend to exhibit general (non-nuptial) sexual dimorphism (Snyder 1908; Murphy 1943).

California Roach are highly variable in most of their characteristics across their range. Brown et al. (1992) measured 14 morphometric variables from eight watersheds around the San Joaquin Valley, including the southern end of the range (Table 1). Using these variables, a discriminant analysis correctly assigned 76% of the individuals to the watershed from which they were collected, suggesting locations were sufficiently isolated from one another to have local adaptations or phenotypic divergence.

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Distribution. Individuals were historically found in most tributaries to the Sacramento and San Joaquin Rivers, including tributaries in the extreme southern San Joaquin Valley (e.g. Kern River), as well as in fringe habitats (backwaters with dense riparian cover) along the main rivers (Moyle 2002; Fig. 1). Fish were rarely found in streams above 1000 m in elevation, presumably restricted by high gradients and natural barriers. In the Tuolumne River, the upstream limit was historically (and still is) Preston Falls at 885 m elevation. The historic distribution in the upper Sacramento River is poorly understood.

Today CA Roach are absent from many streams as the result of habitat change and invasions of alien predators. For example, Moyle & Nichols (1973) and Brown & Moyle (1993) found they were absent from the Fresno River (Fresno Co.) and other tributaries to the San Joaquin River. They were also once common in the mainstem San Joaquin River but are absent today. Moyle (2002) documented their consistent presence in the river at Friant (Fresno Co.) until the construction of Friant Dam in the 1940s. CA Roach are absent from most of their historic range in the Cosumnes River watershed due to the invasion of piscivorous Redeye Bass, Micropterus coosae (Moyle et al. 2003). In the upper Yuba River watershed, they are largely absent as the result of 19 th century hydraulic mining, with the exception of one small tributary to the South Fork Yuba, Kentucky Ravine (Gard & Randall 2004).

The range of CA Roach has also been expanded, presumably through ‘bait bucket’ introductions by anglers. For example, Hetch-Hetchy Reservoir (1,162 m) on the upper Tuolumne River, well above a series of natural barriers, supports a large pelagic population (P. Moyle, unpublished observations). This is unusual because CA Roach do not generally live in reservoirs, especially those with predatory fishes. Interestingly, individuals from this location were found to be admixed with Hitch (Baumsteiger et al. 2017), a factor which may explain their persistence. Soquel Creek and the Cuyama River in southern California support presumed introduced populations, although their origins are also uncertain (Moyle 2002).

It is possible that the ancestor of the widely-distributed CA Roach gave rise to most other Roach species and subspecies but this has not yet been investigated phylogenetically. The ability of these fish to persist in small, often intermittent tributaries presumably led to their colonization of adjacent drainages in a number of areas through capture of interior headwater streams by erosion or tectonic movements (Snyder 1908, 1913; Murphy 1948; Moyle 2002). Because they are relatively intolerant of saline waters, dispersal to coastal streams could not have occurred through ocean waters. However, connections at low elevations may have been possible in some cases when sea levels were lower and estuaries joined the mouths of rivers (Moyle 2002). Similarly in the giant San Francisco Estuary, exchange between salt-water intolerant populations likely occurred during flood years when river outflows were high enough to create freshwater lenses in the surface waters of the estuary (Ayres 1854; Snyder 1905; Murphy 1948; Leidy 2007). During high water periods, fish may also have been able to disperse through flooded marshes on the fringes of the estuary. Today such opportunities for dispersal are largely absent (Moyle et al. 2012).

Status. Moyle et al. (2015) list California Roach as a Species of Special Concern, with an IUCN status of Near–threatened. If CA Roach were a single interbreeding taxon, there would be little danger of immediate extinction because they occur in many streams over a wide area. However, the discovery that CA Roach comprise multiple lineages, some of which are under immediate threats, is of conservation concern. After all, the small, isolated populations that are the most likely to be extirpated also tend to be the most distinctive (Brown et al. 1992). Emerging appreciation for the variation within the taxon (Moyle et al. 1989; Brown et al. 1992; Jones 2001; Jones et al. 2002; Aguilar & Jones 2009; Baumsteiger et al. 2017) has highlighted the need to preserve populations endemic to specific watersheds. On a broader scale, Moyle et al. (2013) regarded the entire taxon as highly vulnerable to extinction in the next century due to massive changes to smaller streams brought on by climate change, the continuing effects of anthropogenic land and water use, and the spread of invasive species.