Rhinichthys nevadensis Gilbert 1893

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 : 517-519

Rhinichthys nevadensis Gilbert 1893 , new common name, Desert Speckled Dace

Rhinichthys (Apocope) nevadensis, Gilbert 1893:230

Agosia nevadensis Jordan and Evermann 1896:310

Agosia nubila carringtoni , Jordan and Evermann 1896:311

Agosia robusta Rutter 1903:148 ; Snyder 1917:2002

Agosia carringtoni: Snyder 1913:70

Apocope robusta Snyder 1918:33 ; Evermann and Clark 1931:55

Rhinichthys osculus robustus: Shapovalov and Dill 1950:387 ; Kimsey and Fisk 1960:46; Hubbs et al. 1979:12; Moyle 2002:161.

Rhinichthys osculus nevadensis Shapovalov and Dill 1950: 387 ; Shapovalov et al. 1981: 25; Hubbs et al 1979:12; Smith et al, 2002: 33; Moyle 2002:161; Mussmann et al. 2020:10805

Holotype: Rhinichthys (Apocope) nevadensis, USNM 46111, 65 mm SL, Ash Meadows, Nye County, Nevada, Amargosa River watershed , March 4,189 1, T. S. Palmer.

Paratypes: USNM 350556 , 3 (42–51 mm SL), March 4,189 1 , T. S. Palmer; and USNM 46112 , 5 , March 3,189 1, A.K. Fisher, both from same locality as holotype .

Diagnosis. Desert Speckled Dace are best recognized as small (adult lengths of 5–9 cm) cyprinoid fish that have the typical Speckled Dace phenotypic characters, inhabit Lahontan, Owens Valley and Death Valley drainages and are a distinct genetic lineage that encompasses three sublineages. The mouth is slightly subterminal, often with a frenum. Meristics and morphometrics are in the ranges shown in Table 3 but are not distinctive. Color is variable but there are usually speckles and blotches on the body which join to form a black lateral band on each side. The band is most prominent underneath each eye, sometimes extending to the snout. We recognize three subspecies, based on genomics and distribution: R. n. nevadensis , R. n. caldera, and R. n. robustus . Each has a separate account.

Description. The complete original description of R. nevadensis is as follows, from Gilbert (1893: 230) although numerical fractions in the original description have been converted to decimals. All morphometric measurements are standardized by dividing into standard length.

“Differing from other known species in the large head, short deep body, very small eye, and the reduction of the outer ventral ray to a mere rudiment. Head, 3.66 [times into] length (varying from 3.5 to 4.0); depth 3.66 (varying from 3.5 to 4.0); D. [dorsal rays],8; A. [anal rays],7; Lat. l. [Lateral line scales] 65. Ventrals apparently with seven rays, the outer one rudimentary, and often detected with difficulty.”

“Body robust, with broad heavy head, the least depth of caudal peduncle less than half the greatest height of body. Greatest depth of head at occiput 5 in length of body. Eye very small, half the interorbital width, which equals distance from tip of snout to middle of eye, and is contained 2.66 times in head.”

“Mouth terminal, very oblique, the lower jaw included, the premaxillaries not at all overlapped by the snout. The maxillary reaches the vertical from front of eye and is one-third length of head. Maxillary barbles [sic] well developed.”

“Scales very irregularly placed and difficult to enumerate. The lateral line is incomplete in adults and usually does not reach to opposite dorsal fin. In the young it is variously developed, often extending though with many interruptions, to end of dorsal or base of caudal. Pores in lateral line (when complete) 58, about 66.”

“Fins small, the pectorals not reaching ventrals, the latter not to vent. Front of dorsal midway between base of caudal and middle of occiput.”

“In spirits, the upper half of sides is speckled and marbled with brown and the belly and lower half of sides immaculate or sparsely spotted. A broad dark lateral stripe usually present, becoming more conspicuous posteriorly, and ending in an obscure black spot on base of tail. A dark stripe sometimes present along middle of lower half of sides. ”

This description is for dace now treated as a population of Amargosa Speckled Dace ( R. nevadensis nevadensis ) from Ash Meadows in Death Valley. It also fits the other two subspecies as well, although R. n. robustus is typically more darkly pigmented and R. n. caldera is typically pale without much dark pigmentation. Sada et al. (1993) compared meristics ( Table 3 ) and morphometrics of dace of all three subspecies and found only small, overlapping differences, which could not be used to distinguish the three groups for identification purposes

Distribution. Desert Speckled Dace are widespread in the southern Lahontan Basin and also inhabit small desert springs and streams in the Owens Valley and Death Valley regions. The common genetic heritage (ancestry) of the three subspecies is the result of late Pleistocene aquatic connections, which allowed the ancestral population(s) to spread throughout the Great Basin and into Death and Owens valleys. During the periods of high rainfall, large inter-connected lakes were formed throughout the Great Basin ( Grayson 1993).

One of the largest lakes was Lake Lahontan. Its remnant lakes and tributaries support Lahontan Speckled Dace to this day. Lake Russell (whose remnant is fishless Mono Lake), drained into Lake Lahontan’s southern end. About 1.3 million years ago, this connection to Lake Lahontan was blocked by vulcanism and Lake Russell subsequently spilled multiple times directly into the Owens River basin ( Reheis et al. 2002). The subsequent eruption of the Long Valley caldera (0.76 mya) formed Long Valley Lake in the upper Owens Basin. Long Valley Lake, and adjacent Adobe Lake, drained into the Owens River which flowed into Owens Lake. Owens Lake spilled into Searles Lake, which drained into the Panamint Valley and Lake Manley, the site of present-day Death Valley ( Grayson 1993). Lake Manly was the ultimate end for the water. Speckled Dace managed to make it through this chain, leaving populations behind in spring systems when dry desert conditions returned. The reverse movement of fish from Lake Manly to the Owens Basin was apparently geologically improbable, given the large waterfalls in the Owens River gorge and elsewhere ( Hildreth & Fierstein 2016). The ancestral dace also colonized the Amargosa River which flowed into Lake Manly from the east by moving upstream from the lake.

The Eastern California Lake Chain, described above, was possible because of the elevational gradient starting at about 2200 m in elevation in the Lake Russell and dropping to sea level in Lake Manly ( Orme 2008). The flow, however, was not continuous because connections between lakes were variable through time. Thus, based on estimates of the timing of lake spills, Lahontan fishes were isolated in the Lake Russell Basin about 1.3 million years ago. This basin spilled numerous times. The last spill was as recently as 100,000 years ago ( Reheis 2002), when the Owens River carried Lahontan fishes to Owens Lake and allowed Speckled Dace and other fishes to colonize streams flowing into the caldera. The last spill event from Owens Lake seems to have been 10–12,000 years ago ( Orme 2008), although the dace had presumably already colonized Lake Manly and the Amargosa River by that time. In the Owens Valley, Long Valley Speckled Dace and the Owens Valley populations of Amargosa Speckled Dace now occupy a few spring systems or artificial refuges. They have been extirpated from most of their historic ranges. Amargosa Desert Speckled Dace apparently were once found throughout the lower elevation reaches of the Owens River and tributaries ( Snyder 1917).

Genetics/Genomics. The genomics-based analysis of Su et al. (2022) supports treating the Desert Speckled Dace as a widely distributed lineage, with three sub-lineages. The major lineage fits our definition of a species. The three sub-lineages can be regarded as subspecies: R. n. nevadensis , R. n. caldera, and R. n. robustus (described below). The analysis also shows that Speckled Dace from the Death Valley and Owens Valley regions share a recent ancestry (via the Amargosa River) but also show some divergence. They are best treated as Distinct Population Segments of R. nevadensis nevadensis .

Notes. This analysis supports the finding that the Desert Speckled Dace is a species with three geographically and genomically defined subspecies. However, most of its distribution is encompassed by R. n. robustus in the Lahontan Basin. See subspecies accounts for more details.

Etymology. Desert Speckled Dace is the new common name we propose for the Speckled Dace species which occurs in the Lahontan Basin and in the Owens and Death Valley systems. These regions are all very arid, and include Death Valley, one of the hottest and driest places on Earth. The first description of this species was based on specimens from Ash Meadows, Nevada, hence nevadensis . Genomics allows us to recognize three subspecies of Desert Speckled Dace that have been isolated from one another, Lahontan Speckled Dace, Amargosa Speckled Dace, and Long Valley Speckled Dace. Both the Lahontan Speckled Dace and the Amargosa Speckled Dace were originally described as species, R. robustus and R. nevadensis , respectively. However, they both also have a long history of being treated as subspecies of R. osculus . R. nevadensis is used as the species name for Desert Speckled Dace because it was described in 1893, nine years before R. robustus was described. The rules of zoological nomenclature declare that the oldest name used in a species description has precedence as the name for the species (International Code of Zoological Nomenclature, 1999, 4 th Edition, Chapter 11, Article 50.4. 1999)