Rhinichthys osculus nevadensis

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General Information
Common Name: 
Amargosa Canyon speckled dace
FID: 
CRO06
Status: 

Class 1. Endangered listing recommended. Amargosa Canyon speckled dace are highly vulnerable to extinction in their native range in the next 50 years, because they are restricted to a single desert stream system which is under constant threat of dewatering, and is heavily invaded by alien fishes. They have not been recorded since 1982.

Life History: 

Speckled dace typically form small feeding aggregations. They are omnivorous; their dietary range includes aquatic and terrestrial insects, other invertebrates, such as snails and microcrustaceans, and filamentous algae (Moyle 1976). In stream systems they are active throughout the year, including the winter months. As a consequence, because growth is continuous throughout the year they are difficult to age by scale analysis. However, length-frequency analysis of dace from various localities suggests that they may live for 5-6 years (Moyle 2002). For a general life history of the speckled dace see the Santa Ana speckled dace account in this report and Moyle (2002).
In Amargosa Canyon, the most frequent size class in May was 52-54 mm TL, but in July smaller fish averaging 31-33 mm were more common (Williams et al. 1982). However, in May there were many small fish (

Habitat Requirements: 

Unlike other speckled dace, which usually prefer running water, the Amargosa Canyon dace prefers pool-like habitat with deep (0.45-0.75 m), slow (

Distribution: 

This population is confined to the Amargosa River in Amargosa Canyon and tributaries to it, especially Willow Creek and Willow Creek Reservoir (Williams et al. 1982). Historically, it was found in a warm spring just north of Tecopa (Miller 1938) but that population is no longer present. Overall, its range has probably been reduced somewhat, but the exact extent is not known.

Abundance Trends: 

During a 1981 survey of the Amargosa Canyon that included the river and Willow Creek, speckled dace comprised 1% of the fishes collected (Williams et al. 1982). Introduced western mosquitofish (Gambusia affinis) comprised 40% of the fish collected. This indicates that the dace are much less abundant than they used to be and are probably declining. There are, however, no historic estimates of abundance nor have there been any recent surveys. In fact, there have been reports of the dace since Williams et al. (1982).

Description: 

Speckled dace are small cyprinids, usually measuring less than 8 cm SL at maturity but occasionally reaching 11 cm SL (Moyle 2002). Although physically variable, they are characterized by a wide caudal peduncle, small scales (47-89 along lateral line), and pointed snout with a small subterminal mouth. At maturity the dorsal fin usually has 8 rays and originates well behind the origin of the pelvic fins (Moyle 2002). The anal fin has 6-8 rays. Pharyngeal teeth (1,4-4,1 or 2,4-4,2) are significantly curved with a minor grinding surface. The maxilla usually has a small barbel at each end. The snout is connected to the upper lip (premaxilla) by a small bridge of skin (frenum). As their common name indicates, most fish larger than 3 cm have distinctive dark speckles on the upper and sides of the body, although some fish from highly turbid waters may lack speckles. Dark blotches present on the side can merge creating what looks like a dark lateral band. A stripe on the head, below the eye, extends to the snout, and there is black a spot on the caudal peduncle. The rest of the body is dusky yellow to olive, with the belly being a paler color. Breeding adults of both sexes have fins tipped by orange or red, while males also have red snouts and lips, and tubercles on the head and pectoral fins.