Rhinichthys nevadensis robustus ( Rutter 1903 ) Moyle & Buckmaster & Su, 2023

Moyle, Peter B., Buckmaster, Nicholas & Su, Yingxin, 2023, Taxonomy of the Speckled Dace Species Complex (Cypriniformes: Leuciscidae, Rhinichthys) in California, USA, Zootaxa 5249 (5), pp. 501-539 : 519-520

Rhinichthys nevadensis robustus ( Rutter 1903) , new combination, Lahontan Speckled Dace

Tables 2 , 1g ; Figs. 1 , 6

Agosia nubila carringtoni Jordan and Evermann 1896:311

Agosia robusta Rutter 1903:148 ; Rutter 1908:139; Snyder 1917:202

Apocope robusta Snyder 1918:33

Apocope robusta Evermann and Clark 1931:55

Rhinichthys osculus robustus Hubbs and Miller 1948 (a, b) and most subsequent publications.

Rhinichthys osculus robustus Hubbs et al. 1974:12

See R. nevadensis for additional synonyms

Holotype: USNM 50589 , collected from Prosser Creek, California, Rutter and Atkinson ( Rutter 1903).

Diagnosis. The Lahontan Speckled Dace fits the image of what Speckled Dace are expected to look like ( Fig. 1 ). It is a small (adults usually <8 cm SL) active fish with blotches on the side that can merge to become a stripe leading to a dark band around the eye. The caudal peduncle is thick, about half the body depth, while the body is subcylindrical (robust). The head is bluntly pointed, with a tiny sub-terminal mouth. Fins are small (the dorsal fin usually has 8 rays, the anal 7 rays). Presence of tiny maxillary barbels at the corners of the mouth is variable as is the presence of a frenum. It is distinguished from the other two subspecies of R. nevadensis by genomics and by its being endemic to the Lahontan Basin in Nevada, Oregon, and California.

Description. The following is the original description from Rutter (1903:148) for Lahontan Speckled Dace. “Body heavy, highest above insertion of pectorals; the ventral outline curved almost as much as the dorsal. Head 3.8 to 4 in body; snout blunt, but little overlapping the premaxillary and never extending beyond it; mouth oblique, barbels usually absent, present on 10 to 50 per cent of specimens from any one locality. Fins small; D. 8; A. 7; pectoral about equal to head behind nostril variable; caudal moderately forked, middle rays two-thirds length of longest; rudimentary caudal rays forming prominent keels along upper and lower edges of tail; margin of anal slightly rounded, the anterior rays not all produced, not extending beyond posterior rays when fin is depressed. Lateral line nearly always incomplete, but with scattered pores frequently extending to base of caudal; scales 56 to 77, varying about 12 in any one locality. Usually two dusky lateral stripes, the upper extending from snout to caudal, the lower branching off from the upper behind the head and ending along base of anal; cheek abruptly silvery below lateral stripe; tinged with orange about lower jaw, upper end of gill-opening, and at base of lower fins (p. 148).

Note that the coloration described above is based on breeding colors. Hubbs et al. (1974) provide descriptions of the variety of pigmentation patterns present in scattered Speckled Dace populations in the Great Basin and elsewhere.

Distribution. Lahontan Speckled Dace are widely distributed in desert basins in northeastern California and northern Nevada ( Fig. 3 ), as described by Hubbs et al. (1974). In California, Rutter (1903) collected specimens from Spring Creek, Willow Creek, Susan River, Little Truckee River, and Prosser Creek, all streams on the western edge of the Lahontan basin. It is also common in Eagle Lake and its inflowing streams (Lassen County) and in the watersheds of the Susan, Truckee, Walker and Carson rivers.The Truckee watershed includes Lake Tahoe and Prosser Creek (tributary to the little Truckee River), the type locality. More broadly, the range of this subspecies includes the drainage of pluvial Lake Lahontan, which covered much of northern Nevada and with fringes in California and Oregon ( Hubbs et al. 1974). This region is mostly Great Basin Desert today and includes Pyramid Lake, Nevada, the largest remnant of Lake Lahontan, and the Humboldt River in Nevada. Wherever there is permanent water in the Lahontan Basin, Speckled Dace are likely to be encountered, including isolated populations in spring systems ( Hubbs and Miller 1948a, Hubbs et al. 1974, Deacon and Williams 1984). They often co-occur with other Lahontan endemic fishes, such as Tahoe Sucker ( Catostomus tahoensis ), Lahontan Redside ( Richardsonius egregius ), Lahontan Tui Chubs ( Siphatales bicolor subspp .) and Lahontan Cutthroat Trout ( Oncorhynchus clarki lewisi ) ( Moyle 2002). In recent years, Lahontan Speckled Dace have managed to colonize the headwaters of the North Fork Mokelumne River (Central Valley watershed) as the result of a water project. Lahontan Redsides were also transferred by this same route ( Garcia and Associates 2000).

Genetics/Genomics. Billman et al. (2010) analyzed mtDNA of dace from the Great Basin; they found support for three distinct lineages (clades): Lahontan, northern Bonneville (Snake River), and southern Bonneville. Smith et al. (2017), using mtDNA, meristics, morphometrics, and fossils, placed all Speckled Dace into three clades, Lahontan, Pacific Northwest (Columbia) and Colorado. Su et al. (2022), using genomics, provide strong support for Lahontan Speckled Dace as a distinct lineage that is a subspecies of Desert Speckled Dace, as are Amargosa Speckled Dace and Long Valley Speckled Dace.

Notes. Rutter (1908) found considerable overlap in morphometrics between Lahontan Speckled Dace and dace from the Sacramento drainage, so treated them together as one species. This move was generally not accepted, presumably because the fish faunas of the two basins are otherwise very different. Comparisons of meristics and other features of Lahontan Speckled Dace with those of other dace species and subspecies (including Amargosa and Long Valley Speckled Dace) reflect that there are no external features to easily distinguish the dace subspecies ( Tables 2 , 3 , Figure 1 ). Our genomic analysis nevertheless shows that Lahontan Speckled Dace is a valid subspecies that is found throughout the Lahontan basin, wherever there is permanent water. The following lines of evidence support this conclusion.

Taxonomy. The Lahontan Speckled Dace was described by Rutter (1903) and recognized as a full species until ichthyologist Carl Hubbs and others started calling it a subspecies, Rhinichthys osculus robustus . This designation was justified by the lack of features easily separating it from other Speckled Dace taxa.

Geography/Geology. The distribution of Lahontan Speckled Dace coincides with the northern part of the region called the Great Basin Desert ( Deacon and Williams 1984; Moyle 2002).

Genomics/genetics. Three genetic/genomic studies have shown that Lahontan Speckled Dace belong to a distinct evolutionary lineage as do the two other subspecies of Desert Speckled Dace ( Oakey et al. 2004; Billman et al, 2010; Su et al., 2022). The long isolation of this subspecies in the region is reflected in the lack of genomic evidence for recent hybridization with other dace species/subspecies.

Etymology. The Lahontan Speckled Dace was originally described by Rutter (1903) as Agosia robusta without explanation of the species name, although he described the body as heavy, perhaps reflecting the roundness of the body in cross-section, the blunt snout, and thick caudal peduncle. Gilbert (1893) also described the Amargosa Speckled Dace as being robust.

Conservation Status. The Lahontan Speckled Dace is widespread and abundant in many places in the Great Basin Desert and in streams and lakes of the Eastern Sierra Nevada. Because streams are increasingly dammed and diverted for human use, dace populations are increasingly fragmented. Speckled Dace are rare in or absent from most reservoirs. The safe status of Lahontan Speckled Dace should therefore not be taken for granted, especially in the face of climate change.

Figures

FIGURE 1. Top: Lahontan Speckled Dace (ca. 70 mm TL) and cover habitat in Taylor Creek, California, a tributary to Lake Tahoe. The body shape, stripe on head, and speckling are characteristic of live fish in many populations from Mexico to Canada that have been considered to be just one species, Speckled Dace (Rhinichthys osculus). Photo by T. L. Taylor, July 17, 1991. Bottom: Preserved specimen of Sacramento Speckled Dace, collected by John Otterbein Snyder from Alameda Creek, California in 1898, showing basic external anatomy. Note the presence of tiny maxillary barbels on head, an example of a distinctive characteristic of some populations. Photo by Jon Fong, California Academy of Sciences, of specimen SU 16172.

FIGURE 3. Current distribution of Rhinichthys in California and adjacent watersheds. The distributions are only approximate but based on occurrence in HUC 12 watersheds. The numbers refer to populations in the Owens Valley and Death Valley that are included in Amargosa Speckled Dace, R. nevadensis nevadensis and can be recognized as Distinct Population Segments (1) Owens Speckled Dace, (2) Oasis Valley Speckled Dace, (3) Ash Meadows Speckled Dace, and (4) Amargosa River Speckled Dace. Long Valley Speckled Dace are a distinct subspecies. Dace have been extirpated from the south San Francisco Bay-Santa Clara Valley region. See text for more specific distributional information. Information for this map was gleaned from Gesch et al. (2002), Patterson and Kelso (2021), Santos et al. (2013), US Census Bureau (2001), USGS (2004, 2013). Speckled Dace are typically present in a limited number of streams, springs and ditches within each mapped region. Map by Amber Manfree.

FIGURE 6. Top. Holotype, Lahontan Speckled Dace, from Rutter (1903). Middle, Long Valley Speckled Dace from Whitmore Marsh, 2014, showing life colors. Photo by Jacob Katz. Bottom: Western Speckled Dace, type specimen, from Evermann and Meek (1898).