Rhinichthys osculus

The following description is from Minckley (1973) and Sublette et al. (1990). The speckled dace is a chunky, rounded minnow. Adults reach lengths of 45-80 mm standard length (SL = length from tip of snout to end of hypural plate) (Wallace 1980). Usually there are 8 dorsal rays (6-9), 13-14 pectoral rays, 8 pelvic rays, and 7 anal rays. There are 60-90 scales along the lateral line. The mouth is subterminal, usually with no frenum. Pharyngeal arches contain teeth in two rows, usually 1,4-4,1 or 2,4-4,2. A single, small barbel is located at the edge of each jaw. Coloration is variable depending on geographic location, but often dark and blotchy dorsally, lighter ventrally. A lateral band extends from the dorsal fin onto the caudal peduncle. Breeding males have an intense red color at the base of paired fins, near the anal fin base, on the lower caudal lobe, near the upper part of the gill cleft, and on the mouth. Breeding tubercles are present on pectoral rays of males. Larval speckled dace from the upper and lower Colorado River basin were described by Snyder (1981) and Winn and Miller (1954), respectively.

In Arizona and New Mexico, the speckled dace is morphologically most similar to Tiaroga cobitis, the loach minnow, with which it often occurs syntopically. The speckled dace differs in having a single barbel at each side of the upper lip and the mouth is relatively larger and less oblique than in loach minnow. The loach minnow possesses more dorsally oriented eyes than does the speckled dace. Other meristic counts are the same or overlap in the two species. Both species have a blotchy appearance, but the speckled dace lacks off-white spots before and after the dorsal fin and on the caudal peduncle.

Smaller specimens of speckled dace might be confused with Agosia chrysogaster, the longfin dace, which is syntopic with the speckled dace in parts of its range. Longfin dace has a long coiled intestine and a black peritoneum; speckled dace has an S-shaped intestine and light peritoneum.

Occurs in many kinds of habitats: riffles, runs, and pools of cool flowing headwaters, creeks, and small to medium rivers with mostly rocky substrates; large and small lakes (rarely); warm, permanent and intermittent streams; and outflows of desert springs (Moyle 1976); usually found in shallow water (averaging about 0.5 m deep or less); in streams, often congregates below riffles and eddies (Minckley 1973). Young tend to occupy edges of streams in slower, shallow water (Cross 1975). Larger adults generally are in relatively quiet water where cover (e.g., overhanging trees, deadfalls, boulders) is available (Minckley 1985).

Stream populations spawn in swift water over rocky substrates. Lake populations spawn in shallow waters with gravel substrate or on gravel edge of riffles in inlet streams (Moyle 1976). In Aravaipa Creek, Arizona, spawning occurred over rapids and riffles, at depths less than 25 cm, over substrates of gravel, cobble, or rubble (Minckley 1981).

Mueller (1984) described spawning behavior of speckled dace in the San Francisco River, New Mexico. Spawning occurred in a 1-m square section of stream recently scoured by human activity. Spawning clusters formed, each with more than 25 fish. Dace thrashed violently (presumable at spawning) and eggs were found at depths to 5 cm. Most eggs were unexposed, attached to undersides of rocks or in interstices between rocks. Territoriality or spawning pairs were not observed.

In the Virgin River (Utah, Arizona, Nevada), speckled dace were collected from 500 m to 1800 m elevation (Cross 1975). Sixty percent were collected in runs, 30 percent in pools, and 10 percent in riffles. Two-thirds of the collections were associated with gravel, rubble, or cobble substrates and one-third with sand and mud. Seventy percent were collected near some type of cover, usually overhanging trees, deadfalls, and boulders. Speckled dace were collected at current speeds averaging 0.43 m/sec (SD = 0.25 m/sec, range 0 to 1 m/sec) and at depths averaging 48 cm (SD = 43 cm).

Speckled dace from the Virgin River (Utah, Arizona, and Nevada) preferred an average temperature of 15.8 C (range 9.5 to 16 C, depending on acclimation temperature) (Deacon et al. 1987). Critical thermal maxima were 30.5, 32.6, and 36.8 C for dace acclimated at 10, 15, and 25 C (Deacon et al. 1987). Rangewide, however, the speckled dace is found at much higher average temperatures, such as 29 C at Ash Meadows, Nevada, 28 C at Pahranagat Valley, Nevada (Deacon and Bradley 1972), and 29.4 C at Kendall Springs in Wyoming (Hubbs and Kuehne 1937).

Lowe et al. (1967) showed that speckled dace, collected from Sonoita Creek, Arizona, were intolerant to elevated temperatures and reduced oxygen levels. Speckled dace were least tolerant to reduced oxygen levels when compared to Agosia chrysogaster, Catostomus clarki, and Cyprinodon macularius (Lowe et al. 1967).

Associated with several different faunas depending on location. In the Gila River drainage, native associates include the spikedace (Meda fulgida), roundtail chub (Gila robusta), loach minnow (Tiaroga cobitis), longfin dace (Agosia chrysogaster), Sonora sucker (Catostomus insignis), desert sucker (Catostomus clarki), and Gila trout (Oncorynchus gilae). Historical associates included the woundfin (Plagopterus argentissimus), bonytail (Gila elegans), squawfish (Ptychocheilus lucius), flannelmouth sucker (Catostomus latipinnis), and razorback sucker (Xyrauchen texanus), all now extirpated from the Gila River basin.

Populations show large fluctuations in size (Minckley 1969, Deacon and Bradley 1972). LaBounty and Minckley (1972) noted that increasing populations of longfin dace may result in decreasing populations of speckled dace in areas of overlap at intermediate elevations. There is not enough data to understand the nature of this relationship (i.e., whether or not it is cause-effect).

Predators include introduced trouts (Oncorynchus and Salmo spp.) in the Colorado River mainstream, flathead catfish (Pylodictus olivaris) in the Salt River basin, and also introduced basses (Micropterus spp.) and green sunfish (Chaenobryttus cyanellus) (Minckley 1985). Thamnophis cyrtopsis (black-necked garter snake) is known to feed on speckled dace (John 1964).

Mpoame and Rinne (1983) recorded the protozoan Ichthyopthirius multifiliis, trematode Ornithodiplostomum ptychocheilus, and the cestode Ligula intestinalis as parasites of speckled dace in Aravaipa and Hurricane creeks, Arizona.

Generally occurs in small, loose groups.

Cross (1975) collected ripe females in late June and mid-July 1973 from the Virgin River drainage in Utah. In Aravaipa Creek, Arizona, speckled dace were collected in breeding coloration or with tubercles from December to August, with mature gonads from November to March, or seen engaged in spawning activities from January to April. Larvae were collected from January to April.

John (1963) studied reproduction in Cave Creek, Chiricahua Mountains, Arizona. Females matured at two years of age. Peaks in reproductive activity were in early spring and late summer. John believed spawning efforts were triggered by flash floods. Males defended territories, and activities of the male often resulted in circular, clean gravel areas that John (1963) called nests. A female entered a defended area and partially buried or wedged herself under the edge of a stone. Males took positions next to the buried female and the pair or group vibrated for a few seconds, after which the female departed. A female entered a nest several times, depositing a portion of her ripe eggs during each spawning event. John (1963) gave data for the total number of eggs laid in an aquarium by each of eight females. From these data, Vives calculated that the number of eggs laid was related to standard length by the equation: number of eggs laid = -264.41 + 10.45 SL (mm) (R- squared = 0.89, p < 0.001). Females ranged from 45 to 75 mm SL and numbers of eggs laid ranged from 174 to 514. Eggs hatched in 6 days at 18 to 19 C under laboratory conditions.

Maximum age of speckled dace in streams of the Chiricahua Mountains is 3 years (John 1964). Moyle et al. (1989) stated that some may live up to 5-6 years.

Females from the Kettle River, British Columbia, Canada, did not mature until the end of their second year (Peden and Hughes 1981).