By Peter B. Moyle, Nicholas Buckmaster, and Yingxin Su

Lulu Miller in her wonderful 2020 book, Why Fish Don’t Exist, describes how fish exist to us humans only if they have been assigned proper names. The Santa Ana Speckled Dace is a local case in point. This small fish has been living in southern California streams for about a million years, yet has been largely ignored because it was assumed to be just another population of the Speckled Dace. This dace has been regarded as the most widely distributed ‘true’ freshwater fish species in western North America, found in streams and lakes from Canada to Mexico and California. Speckled Dace from throughout this vast range all look alike – blunted-snouted minnows with a tiny mouth and eyes, a nearly cylindrical body, wide caudal peduncle, and active behavior. They are often covered with speckles that coalesce into a dark band, either under or through the eyes. They typically locate under rocks during the day and emerge to forage on invertebrates at night, so are easy to overlook.

This blog is an announcement that the Santa Ana Speckled Dace exists, and now has an official name, which includes its new scientific name, Rhinichthys gabrielino (Moyle et al. 2023). Rhin-ichthys means “snout-fish” while gabielino honors the native peoples who lived comfortably with Santa Ana Speckled Dace for thousands of years. Today this fish is missing from about half its historic habitats in the Los Angeles, San Gabriel, and Santa Ana rivers [see map below]. Because it now has an official name, it is more likely to gain the attention of conservation agencies, much like the Santa Ana Sucker (Pantoseus santannae), which is listed as a Threatened species under state and federal Endangered Species Acts. A petition to similarly list the Santa Ana Speckled Dace has been filed by the Center for Biological Diversity. After thriving in the Los Angeles Region for a million years, disregard for its welfare by people may lead to its extinction in the next 50 years or less.

Moyle et al. (2023) used genomic (DNA) analyses as a major basis for providing, not only a name for Santa Ana Speckled Dace, but for all dace populations in California. There are now two other species of Speckled Dace in California, each with three subspecies (below). All are cryptic and similar, so hard to tell apart, unless you look at their DNA.

Santa Ana Speckled Dace, Rhinichthys gabrielino, new species

Desert Speckled Dace, Rhinichthys nevadensis, new common name

            Lahontan Speckled Dace, R. nevadensis robustus, new combination

            Amargosa Speckled Dace, R. nevadensis nevadensis, new combination

            Long Valley Speckled Dace, R. n. caldera, new subspecies

Western Speckled Dace, Rhinichthys klamathensis, resurrected species

            Klamath Speckled Dace, R. klamathensis klamathensis new combination

            Sacramento Speckled Dace, R. klamathensis achomawi new subspecies

            Warner Speckled Dace R. klamathensis goyatoka new subspecies

What follows is an explanation of how we arrived at these names. First, I determined which populations of dace in California might merit species/subspecies status based on review of an abundance of previous studies. These studies used standard morphometrics and meristics, mitochondrial DNA and knowledge of the geology and zoogeography of the western USA to try to find names for the scattered Speckled Dace populations, mostly without success. The literature review showed that Speckled Dace in California were indeed cryptic species, with no obvious characters separating populations in regions long isolated from one another.

Second, Su et al. (2022) performed an analysis of dace genomics which required obtaining samples of Speckled Dace tissues from likely distinct populations in the state, plus some outside populations for comparison. The basic hypothesis tested was that Speckled Dace in California were divided up into three evolutionary lineages, each representing a separate colonization of California and long isolation from one another: Lahontan, Klamath-Sacramento, Southern California. The results of the genome analysis, using methods described in Su et al. (2022), largely validated these lineages and revealed likely species and subspecies. The determination of species and subspecies was based on phylogenetic trees generated by the analyses. Branches on each tree represent evolutionary lineages leading to isolated populations that we can recognize as species and subspecies.We therefore were able to label lineages with broad genomic separationfrom other lineages as species and geographically isolated lineages with less genomic differentiation as subspecies. See Su et al. (2022) and Moyle et al.(2023) for details on the methods. Once the genomics analysis was finished, Buckmaster reviewed the latest geologic information to see if the geologic history was reflected in the DNA-based branching; it was.

The species and subspecies that came out of this analysis are each distinctive in their own way. The Santa Ana Speckled Dace were the example that opened this blog, so here are some comments on the rest of the speckled dace taxa we described or unveiled. Distribution of each taxon is shown on map at end of text.

Desert Speckled Dace is a new common name for all the dace found in the Death Valley-Owens Valley region and over a vast area of the Great Basin, mostly in Nevada and California. The scientific name originally applied only to Speckled Dace in the Death Valley region which our genomics study showed were most closely related to Lahontan Speckled Dace. They tend to be found in any waterway with permanent water, despite the great distances of desert often separating populations. This broad distribution reflects that during the Pleistocene period the region was much wetter and now-dry basins and connecting streams were full of water. Genomics revealed three subspecies.

Lahontan Speckled Dace was originally described as a full species inhabiting much of the Great Basin; it was demoted to a subspecies by later workers, mainly because it could not be told apart using non-genetic techniques from Speckled Dace from other watersheds, such as the Sacramento. It inhabits a wide variety of habitats including Lake Tahoe. Today the Lahontan Speckled Dace is considered to be a subspecies of R. nevadensis, rather than R. osculus.

Amargosa Speckled Dace is the name for dace inhabiting springs, small streams, and ditches in Death and Owens valleys. The geologic history has the Owens and Death Valley regions once connected by the Amargosa River, now mostly dry. All these populations are threatened with extinction from various factors, but only the Death Valley populations are listed under the federal ESA. All should now be included in the listing.

Long Valley Speckled Dace is a new subspecies that is native to small streams and ditches of the Long Valley region. This region was shaped by a volcanic caldera – the result of an eruption that occurred about 750,000 years ago. The scientific name we gave to this fish is consequently R. nevadensis caldera. Today, despite having survived that massive eruption, the Long Valley Speckled Dace is likely the most endangered fish in California. It has just one small population remaining in its native range, in the marshy outflow of a public swimming pool, operated by the Town of Mammoth Lakes. The pool is fed by a hot spring, which formerly flowed directly onto the marsh. A second population lives in a small pond outside the native range, at the White Mountain Research Station, in which everything is artificial including the pumped water supply and the old tires which form the principal cover for the fish. Survival in both places depends on the continuous attention of those who control the water supply (Moyle et al. 2015).

Western Speckled Dace is the name used by Markle (2020) and others for the dace that live in the combined immense watersheds of the Klamath and Sacramento Rivers, plus the Warner Valley and some small coastal drainages in southern California, north of those occupied by the Santa Ana Speckled Dace. This dace was first described as just the Klamath Speckled Dace (hence R. klamathensis) but our genomics study showed that the dace that inhabited streams over a broader area were part of the same evolutionary lineage. See Moyle et al. (2023) for further explanation.

Klamath Speckled Dace are perhaps the most abundant and widespread ‘true’ freshwater fish in the Klamath River watershed in Oregon and California. It has also been introduced into the Eel River, a California watershed previously without Speckled Dace.

Sacramento Speckled Dace so baffled early ichthyologists in California by its similarity to Lahontan Speckled Dace (and others) that it was ignored, even by David Starr Jordan. Jordan was the best-known ichthyologist in the world during his day, who named hundreds of species (Miller 2020). Sacramento Speckled Dace lived in streams close to his doorstep at Stanford University but the best he could do was to say “These California and Nevada forms may be distinct species, but if so, we are unable to define them (Jordan and Evermann 1896:312)”. Sacramento Speckled Dace are abundant and widespread in the Sacramento watershed and managed to colonize rivers as far south as the Santa Maria River. They have disappeared from a number of streams in which they once lived, suggesting that many populations are not secure.

Warner Speckled Dace are known only from streams that flow into the arid Warner Valley, Oregon, including Twelve Mile Creek which has its headwaters in California. The watershed has been heavily invaded by non-native fishes, so the dace (and other endemic fishes) need protection.

Conclusion

Our findings demonstrate the need to conserve the diversity of forms and taxa in this fascinating group of small fishes; if action is not taken to protect them and their habitats, many will disappear. It is therefore important to assign names to the diverse lineages, as we have done for California populations (Moyle et. al. 2023). They all still exist today but only with our sufferance. We can only hope, given the rapid changes taking place on this planet today, that we humans will allow some humble Speckled Dace species and subspecies to survive into the next century and with them the diverse aquatic biota that share their habitats.

Peter Moyle is an emeritus professor in the Center for Watershed Sciences and Department of Wildlife, Fish and Conservation Biology, University of California, Davis. Yingxin Su is a graduate student in the Animal Biology Graduate Group, University of California, Davis. Nicholas Buckmaster is Fisheries Program Supervisor for the Inland Desert Region, California Department of Fish and Wildlife, Bishop, California.

Further reading

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

Center for Biological Diversity (2020) Petition to List Three Populations of Speckled Dace (Rhinichthys osculus) in the Death Valley Region under the Endangered Species Act: Amargosa Canyon Speckled Dace, Long Valley Speckled Dace, Owens Speckled Dace. Submitted to US Fish and Wildlife Service, 8 June 2020, 1–48.

Jordan, D.S. & Evermann, B.W. (1896) The Fishes of North and Middle America. Bulletin, US National Museum, 47, Part 1, 1–1240.

Leidy, R.A. & Moyle, P.B. (2021) Keeping up with the status of freshwater fishes: a California (USA) perspective. Conservation Science and Practice, 3 (8), e474. https://doi.org/10.1111/csp2.474

Markle, D.F. (2016) A Guide to the Freshwater Fishes of Oregon. Oregon State University Press, Corvallis, Oregon, 140 pp.

Miller, L. (2020) Why Fish Don’t Exist: a Story of Loss, Love, and the Hidden Order of Life. New York: Simon & Schuster, 225 pp.

Moyle, P.B. (2002) Inland Fishes of California, Revised and Expanded. University of California Press, Berkeley, California, 405 pp.

Moyle, P.B., Buckmaster, N. and Su, Y. 2023. Taxonomy of the Speckled Dace species complex (Cypriniformes: Leuciscidae, Rhinichthys) in California, USA. Zootaxa https://doi.org/10.11646/zootaxa.5249.5.1

Moyle, P.B. & Campbell, M.A. (2022) Cryptic species of freshwater sculpin (Cottidae: Cottus) in California. Zootaxa, 5154 (5), 501–507. https://doi.org/10.11646/zootaxa.5154.5.1

Moyle, P.B., Quiñones, R.M., Katz, J.V.E, & Weaver, J. (2015) Fish Species of Special Concern in California. 3rd Edition. Sacramento, California Department of Fish and Wildlife. Available from: https://wildlife.ca.gov/Conservation/SSC/Fishes (accessed 8 February 2023)

Su, Y., Moyle, P.B., Campbell, M.A., Finger, A.J., O’Rourke, S., Baumsteiger, J. & Miller, M.R. (2022) Population genomic analysis of the Speckled Dace species complex identifies three distinct lineages in California. Transactions of American Fisheries Society, 151, 695–710. https://doi.org/10.1002/tafs.10388