TN00351 BLACKNOSE DACE RHINICHTHYS ATRATULUS
Physical description: This is a small robust minnow with tiny scales, a frenum and a ventral mouth with abarbel at each corner. The adults are usually from 40-70 mm SL. The body is somewhat stocky and the dorsal fin origin is well posterior to the pelvic origin and sometimes posterior to the pelvic base. The head is moderate, the eye is small and the snout is downsloped, slightly overhanging the mouth. The mouth has fleshy lips. The nuptial male has small tubercles often densely distributed on the head, dorsum, snout and upper operculum. The body has small tubercles except on the breast. The pectoral fins have thickened pads on the rays and the pelvic fin is tuberculate. The male genital papilla is not obvious and the female papilla is protruding with the anal papilla. The back of a gravid female is somewhat humped predorsally. There are 2,4-4,2 pharyngeal teeth and the lateral line is complete with (23)24-26 scales. There are (11)12-13(14) upper caudal peduncle scales, (8)9 dorsal rays (7)8(9) anal rays and (12)13-15(16) pectoral rays. The breast and belly are fully scaled. The dorsum of the nuptial male is medium or dark olive with scattered black scales and flecks of bronze or green iridescence. The supralateral stripe is tan, bronze or bronze- rust and the midlateral stripe is rust-orange, sometimes with scattered black scales or a dusky black pigment. The lower side of the venter is silver-white or may have a yellow wash. The head dorsum and snout are dusky olive with the preocular bar and band surrounding the snout black. The horizontal eye bar and upper opercular mark are black. The chin, cheek and lower opercle are silver-white or pale yellow. The dorsal caudal and anal fins have a very pale amber-yellow wash. The basicaudal spot is black. The pelvic is pale orange or red-orange and the pectoral is bright orange-red *4205*. Reproduction: Breeding occurs in New York from late May to early June, and another source reports spawning from April to May *1471,1638*. In Virginia, they spawn from May through July in water from 15.6-22 degrees C. They spawn over sand and gravel in shallow water in a current from 20-45 cm per second *4205*. Incubation lasts 7 days at 18.5 degrees C *2252*. There are 375-2500 eggs per female per period *4205*. This species is mature at 2 or 3 years and the maximum longevity is age 3 *4205*. R. a. atratulus does not build a nest but it does defend a territory during the spawning period. Aggressiveness between males occurs when males cluster around one female before one male is chosen as a mate. There is no definite courtship behavior but the male may swim repeatedly below, in front of, or above the female prior to spawning. The male and female may spawn several times in one period before female returns to deeper waters. Both may rest on the bottom between spawning acts, and the female may spawn with several males. The eggs are broadcast carelessly. The male assumes a parallel position to the female, and throws his tail over female's and vibrates his body rapidly. After spawning, the male may prod through the streambed for eggs and eat some. Males are known to consort on riffles, and most spawning occurs in morning hours decreasing towards noon *1471,1617,1616*. R. a. obtusus does not build a nest, defends no territory and exhibits no aggression between males. The males sometimes display 'leading' behavior of prodding a female to a spawning site, and spawning occurs close to the surface and the act itself carries both to the surface where they separate and return to original site to repeat the act. After spawning, the female returns to deeper waters to rest. Most spawning occurs between 1100-1600 hours with a peak at 1300 hours. After spawning, the males root for the eggs and may eat them. This is more severe than with R. a. atratulus. The males may consort on riffles *1616*. The minimum breeding age is 2 years *1616*. Behavior: They often feed in benthic region of the stream, and are omnivorous and opportunistic *4205,1620,1623,1196*. R. a. obtusus spawns in small streams with a flow from 5-15 cubic feet/second, and a water temperature from 15.5-18 degrees C, on a steep gradient with a bottom of large boulders or flat slab rock with lesser amounts of rubble, gravel and sand *1616. Newly hatched larvae are from 4.9-5.7 mm TL (average=5.5 mm), and postlarval stages are begun at 7.2 mm TL. The late postlarval phase is at 14.5 mm TL *2252*. In daylight they are not as wary of predator presence, showing a greater avoidance at night. In an artificial setting in the absence of predator boulder habitat was prefered. In predator presence faster stream currents were prefered *1628,1622*. ORIGIN: This species is native in Virginia *4205*. Three subspecies are recognized within this range: 1) Rhinichthys atratulus obtusus, 2) R. a. atratulus , and 3) R. a. meleagris *JK14*. Population parameters: The growth formula for males is; Y=-0.715 + 0.0469X; and for females Y=-0.192 + 0.385X; where X is standard length in mm and Y is age in years also Y=10.665 + 0.7901X where X is scale radius in mm (scales of the type with a distinct pointed crown) and y is total length in mm *1630,1633*. Aquatic/terrestrial associations: This is an important prey species of trout *1623,1471,1634,1633,1637*. No natural hybrids are known to exist *4205* because of 1) differences in species spawning site (bottom type and water velocity), 2) males show preference for conspecifics, and 3) females only are receptive to courtship behavior of male conspecifics *1632,1624*. TN00351PHYSICAL DESCRIPTION: JUVENILES APPEAR SIMILAR TO SEMOTILUS SPP., WHICH HAVE PROTRACTILE PREMAXILLAE, AND TO CAMPOSTOMA SPP. WHICH HAVE PROTRACTILE PREMAXILLAE AND A BLACK PERITONEUM *TN5057*
| Life History |
References for Life History Codes
1470, 1617, 835, 1471, 1638, 1630, 1616, 2252, 1117, 1620, 1623, 1196, 1628, 1622, 1632, 1624, 1633, 4204
Comments on Life History Codes
With regard to subspecies identification and spawning habits there are conflicting reports from sources *1616* and *1617* and also *1616* and *1632*.