by Peter B. Moyle

If you inspect small streams in northern California, including those that seem too small or warm for any fish, you will often see minnows swimming in the clear water. Chances are you are seeing a very distinctive native Californian, usually called California roach.  This fish is a complex of species that occurs as far north as Oregon tributaries to Goose Lake and is widespread in tributaries to the Sacramento and San Joaquin rivers, as well as in rivers along the coast from the Eel River to Monterey.

“California Roach” is the name originally given to some minnows collected in 1854 from the San Joaquin River.  When the great Stanford ichthyologists David Starr Jordan and Barton Warren Evermann put these fish into their grand monograph Fishes of North and Middle America, they decided it looked like the roach (Rutilus rutilus), a common minnow in England and Europe.  They then gave it the scientific name Rutilus symmetricus.  While the relationship to European roach was dismissed by John O. Snyder in 1913, the unfortunate common name of “roach” stuck.  Snyder placed California Roach in its own genus, Hesperoleucus, and divided it into six species, based on body shape and counts of fin rays and scales (see Table).  His species were also based on the isolation of their home waters from other watersheds, which would prevent interbreeding.

Because roaches are small inconspicuous fishes, little formal attention was paid to their taxonomy (or status).  By the 1950s, there seemed to be a general consensus that Snyder’s species were at best subspecies and the California roach was back to one species.  This was reflected in the classification presented in my 2002 book, Inland Fishes of California, although the species was divided into eight subspecies.   Then, Andres Aquilar and Joe Jones (2009) looked at populations that were part of this ‘species complex’ using mitochondrial and nuclear DNA. Their analysis indicated that two of Snyder’s species, northern roach and Gualala roach, were strongly supported as ‘good’ species.  The other six subspecies I listed in 2002 were at least supported as distinct genetic units by their analysis.

To clarify the relationships among the species more firmly, new techniques in genomics were brought to play.  This effort was led by Jason Baumsteiger, a postdoctoral scholar at the Center for Watershed Sciences and in the genomics laboratory of Mike Miller.  He performed restriction-site associated DNA (RAD) sequencing on roach samples collected throughout California to discover and genotype thousands of single nucleotide polymorphism (SNPs) (see Baumsteiger et al.  2017). This detailed examination of the genomes of roaches from throughout their range allowed determination of how much each population had diverged from other populations.  Among other things, it allowed for ‘rules’ to determine which populations were species, subspecies, or distinct population segments.

Distinct population segment (DPS) designations are based on the use of DPS designations under the national Endangered Species Act; they are isolated populations that are distinctive, but not quite different enough so to be called species or subspecies. DPS designations are widely used for determining whether or not salmon and steelhead populations are eligible for protection under the ESA.

The application of genomics to the taxonomic relationships of roach populations (Baumsteiger and Moyle 2019) resulted in our recognition of five species, four subspecies, and 5 distinct population segments (Table 1). The five species each have distinctive, interesting features.

The California roach is the most widespread species, historically found in streams throughout the Central Valley, with many opportunities for adaptation to local conditions, such as those found in the Kaweah River (hence the Kaweah roach DPS). It appears to be losing these locally-adapted populations rapidly, however, as they become increasingly isolated by dams and damage to streams, and by invasions of their small stream refuges by green sunfish and other non-native predators.

The Clear Lake roach is a bit of mystery because it a perfect hybrid between coastal roach and California roach.  This fits the geologic history of the region, which has been alternately connected to the Russian River and to the Sacramento River. Presumably representatives from both watersheds made it into the Clear Lake basin at times and hybridized.  The hybrid was apparently superior to either parent species in its ability to persist in streams tributary to Clear Lake.  Today, the Clear Lake roach is more isolated than ever, because the lake is full of non-native predatory fishes.

Hybridization also has led to the development of new species in the northern roach.  This roach inhabits small streams and springs of the upper Pit River basin and looks like other roach species.  So we were surprised when the genomics study showed that about 80% of the genome was like that of the hitch, a related species in a different genus (Lavinia exilicauda).  This seems to have been from an ancient hybridization, perhaps when Sacramento Valley fishes invaded the Pit River region thousands of years ago. Curiously, we also found that the roach-like fish abundant in Hetch-Hetchy Reservoir, on the upper Tuolumne River, also are hitch-roach hybrids even though they were introduced into the reservoir by persons unknown.

The southern coastal roach is also known to hybridize with hitch, where the two species occur together naturally, but these hybrids seem unimportant to the populations of both species. The presence of subspecies and DPSs in the coastal roach distribution reflects the isolation of coastal watersheds from one another with enough connections in the past to keep populations from differentiating enough to be labeled species.  This also makes the Gualala roach a bit of an anomaly, given that watersheds on both sides of the Gualala River contain coastal roach.   The northern coastal roach also shows how rapidly a species can spread when introduced into new watershed, in this case the Eel River. These roach, probably introduced in the 1960s, now occupy most of the accessible habitat in the Eel, one of California’s largest watersheds; the genomic study indicates that they came from fish in the Russian River roach DPS, just to the south, so were pre-adapted for conditions in the Eel River.

This study of small fishes demonstrates again the high endemism in fishes that are adapted to the special, often harsh, conditions in California streams.  This surprising diversity is another example of what makes California special and needing of a well-supported, state-wide conservation strategy. The roach species complex is also good example of hidden biodiversity revealed by new genetic techniques.  Modern genomics can support conventional taxonomic methods to designate species, subspecies, and DPSs and should improve our ability to conserve California’s richness of fishes.

Northern roach. Photo by Stewart Reid

Further readings

Baumsteiger, J. and P. B. Moyle. 2019. A reappraisal of the California Roach/Hitch (Cypriniformes, Cyprinidae, Hesperoleucus/Lavinia) species complex. Zootaxa 4543 (2): 2221-240. https://www.mapress.com/j/zt/article/view/zootaxa.4543.2.3  (available as open-access download)

Baumsteiger, J., P. B. Moyle, A. Aguilar, S. M. O’Rourke, and M. R. Miller. 2017. Genomics clarifies taxonomic boundaries in a difficult species complex. PLoS ONE 12(12): e0189417. https://doi.org/10.1371/journal.pone.0189417 (available as open access download)

Moyle, P.B. 2002. Inland Fishes of California.  University of California Press, Berkeley.

Peter B. Moyle is a UC Davis Professor Emeritus of fish biology and an associate director of the Center for Watershed Sciences.

Classic California roach habitat.  Dye Creek, Tehama County, July 2014