Hybognathus Placitus Research Articles

Sexual Dimorphism in Plains Minnow,Hybognathus placitus

Abstract Hybognathus placitus collected from several west Texas streams exhibit sexual dimorphism in body form, which is unusual in cyprinids. Seventeen morphological measurements, including standard length, were made on 62 specimens and analyzed for sexual dimorphism. Partial warp scores were used to describe sexual dimorphism in body shape. There was no difference in standard length between males and females (ANOVA, P = 0.9038, F1,60 = 0.0147), but there was a highly significant (MANOVA, F1,60 = 4.78, P < 0.001) sexual dimorphism in body shape. Overall, males have relatively longer first dorsal fin rays, larger heads, and caudal peduncles, whereas females are deeper bodied and have relatively longer trunks, from the pelvic fin insertion to the anal vent. Differences between male and female H. placitus in length of the first dorsal fin ray are readily apparent and can potentially be used for field identification.

Changes in the Canadian River Fish Assemblage Associated with Reservoir Construction

ABSTRACT The fish assemblage of the Canadian River in Texas historically was dominated by Hybognathus placitus and Notropis girardi. These species represented > 90% of fishes collected from the Canadian River in 1954–1955. Construction of two reservoirs on the Canadian River in the 1960s (Ute Reservoir, New Mexico, 1962; Lake Meredith, Texas, 1965) altered hydrologic conditions in the river and affected the fish assemblage. Downstream from Ute Reservoir, mean annual discharge decreased by about 38% after impoundment, but H. placitus, N. girardi, and other mainstem species still dominate the assemblage. Downstream from Lake Meredith, mean annual discharge decreased by 76% and the historic mainstem fish assemblage has been almost completely replaced by species that formerly were restricted to tributary streams. The magnitude of post-impoundment changes in the fish assemblage of the Canadian River appears to be related to the degree that discharge has declined, especially during the spawning season.

Acute toxicity of Rodeo� herbicide to Rio Grande silvery minnow as estimated by surrogate species: Plains minnow and fathead minnow

Use of Rodeo® herbicide (53.8% glyphosate, active ingredient) to control vegetation in or along irrigation canals in the Rio Grande basin in New Mexico has become a concern because of potential for populations of a federally endangered species, the Rio Grande silvery minnow (Hybognathus amarus), to be exposed. To investigate the potential for adverse effects, toxicity of Rodeo® herbicide was estimated by conducting 96-h renewal-acute toxicity tests with a closely related species, plains minnow (Hybognathus placitus), and a standard laboratory animal, fathead minnow (Pimephales promelas). Rodeo® herbicide had no effect on survival of plains minnow or fathead minnow at concentrations as high as 1,000 mg/L; thus, no-observed-acute-effect concentrations (NOAEC) for both species were 1,000 mg/L. Direct estimates of toxicity of Rodeo® herbicide to Rio Grande silvery minnow were not possible because the species was not available for testing. However, the similarity of responses by plains minnow and fathead minnow suggests that 1,000 mg/L Rodeo® herbicide is an acceptable estimate of the 96-h NOAEC for Rio Grande silvery minnow.

Lotic Fish-Community Structure Following Transition from Severe Drought to High Discharge

ABSTRACT A survey of fishes in the Little Missouri River, North Dakota, was made in July of the unusually wet summer of 1993, following a six-year period of drought. During the nine-day study period, water velocities were high (0.4 to 0.87 m/s), and water temperatures, levels, and discharges fluctuated dramatically in response to rainfall. Only thirteen species of fishes were collected within the 190-km study reach. Of these, only three were found regularly; the others were collected in unusual habitats such as small tributary streams and beaver dams. The three common species (Platygobio gracilis, Hybognathus placitus, and Rhinichthys cataructae) comprised 95% of individuals captured and are known to be well adapted to high flow. The fish community was somewhat different and much less diverse than in the past, possibly due to the preceding drought, high discharge, or rapid transition between them. Ten species found previously were not collected; five of these were abundant. Six species collected were not previously found in the study reach and two of these (Phoxinus eos and Pimephales notatus) are apparently new records for the Little Missouri River. The sturgeon chub (Macrhybopsis gelida) was not collected, even though it was common in the Little Missouri River as recently as the late 1970s, and is well adapted to high flow and turbid water.

Reproductive Ecology and Population Structure of the Plains Minnow, Hybognathus placitus (Pisces: Cyprinidae), in Central Oklahoma

-We described the reproductive biology and population structure of the plains minnow (Hybognathus placitus) during 2 yr in the Cimarron River, Oklahoma. Monthly changes in gonadal weights and mean ovum diameters revealed that the spawning season of H. placitus was prolonged, beginning in spring and ending in late summer. Two peaks in reproductive activity, one in May and the second during midsummer, occurred both years. Spawning in both years coincided with high or receding flows. Most male and female H. placitus began to mature sexually at 45-50 mm SL. The sex ratio did not differ meaningfully from 1:1; males and females were similarly sized. Numbers of mature ova were correlated with standard length and weight ranging from 417 to 4134 for females 51 to 87 mm SL. Length-frequency distributions revealed that H. placitus was short-lived, with most individuals reproducing and dying in their second summer.

Comparison of a Pharyngeal Filtering Apparatus in Seven Species of the Herbivorous Cyprinid Genus, Hybognathus (Pisces: Cyprinidae)

In all seven species of the herbivorous cyprinid genus Hybognathus, pharyngeal taste buds or papillae are arranged in a pattern that suggests a filtering apparatus for trapping diatoms and other small food items. The dorsal pharynx has a patch of small papillae that grades smoothly into larger, posterior buds. Ventrally, prominent transverse ridges cross the first, second, and third gill arches, joining anterior gill rakers to those on the posterior border of the arch. Proximally, the ridges merge into V-shaped flaps covering the basibranchials. The largest of these, termed the major comb, is associated with the first gill arch, and typically bears marginal and surface papillae. The minor comb, associated with the second arch, is smaller and bears marginal papillae. Proximal gill rakers of the second arch, located between the major and minor combs, have rows of papillae, and merge into a central, random patch of papillae. None of the 40 other nearctic cyprinid species surveyed, including Dionda episcopa, D. diaboli, and D. erimyzonops, has comparable pharyngeal modifications. Six counted variables and one measurement, major comb width, were used to make intra- and interspecific comparisons. Hybognathus hankinsoni has consistently low values for counted variables. Hybognathus nuchalis has high values for counted variables and is most similar to H. argyritis. Hybognathus placitus is most similar to H. amarus. Hybognathus hayi is the most distinct species in the genus, but is similar to H. regius in two variables including major comb width. Discriminant analysis classified 92.02% of specimens correctly, indicating that the variation observed in these structures is probably species-specific.

Reproductive Cycle of the Plains Minnow, Hybognathus placitus (Cyprinidae), in the Cimarron river, Oklahoma

Reproductive Cycle of the Plains Minnow, Hybognathus placitus (Cyprinidae), in the Cimarron river, Oklahoma

Interdependence of Acute Temperature Preference and Respiration in the Plains Minnow

Although the temperature preferences of fishes in air-saturated water have been studied intensively, very little is known of fishesˈ preferred temperatures in waters that are oxygen-deficient. Plains minnows Hybognathus placitus acclimated near 21 C selected 30 C in a horizontal temperature gradient when dissolved oxygen was maintained between 5 and 9 mg˙liter−1. But when dissolved oxygen was lower, the acutely preferred temperature declined-from near 30 C at 4.8 mg˙liter−1 to 17 C at 2 mg˙liter−1. Subsequent experiments on routine metabolism of plains minnows at various constant temperatures between 16.5 and 29 C gave results consistent with the following hypothesis: In oxygen-deficient water, the plains minnow prefers the highest temperature (less than 30 C) at which it can operate within the zone of respiratory independence. In nature, a reduction of acutely preferred temperature would reduce oxygen demand and might lead the fish into more highly oxygenated water. Received October 22, 1982 Accepted May 14, 1984

Forage Fish Assemblages in the Brazos River Upstream and Downstream from Possum Kingdom Reservoir, Texas

ABSTRACT The forage fish assemblage of the Brazos River was sampled at one location above and four locations below Possum Kingdom Reservoir each month for one year. A total of 13,936 individuals representing 18 species, 14 genera and five families were collected. Five of these species, Notropis stramineus, Notropis atherinoides, Hybognathus placitus, Hybopsis aestivalis and Cyprinodon rubrofluviatilis were found only upstream from Possum Kingdom Reservoir. Hybognatus placitus accounted for 45% of fish captured at the upstream site. In contrast, nine species were collected exclusively in the tailwaters, including Etheostoma spectabile, Percina sciera, Campostoma anomalum, Notropis venustus, Pimephales notatus, Labidesthes sicculus and Fundulus notatus. Only four species were obtained at all five stations—Gambusia affinis, Menidia beryllina, Pimephales vigilax and Notropis lutrensis. N. lutrensis was the most common tailwater species equalling 87.9% of the total downstream catch. Median species diversity in...

Habitat Partitioning in the Fish Community of a Southwestern River

Patterns of habitat partitioning and spatial overlap are docu- mented for the fishes of an environmentally unstable southwestern river. Notropis lutrensis (red shiner), Notropis girardi (Arkansas River shiner), Hybognathus placitus (plains minnow), and Gambusia affinis (mosquitofish) numerically dom- inated the fish fauna; few centrarchids or other large species were present. While the dominant species showed some spatial segregation at most times, their habitat use was transitory, changing as environmental conditions changed. The dominant species made wide use of the available habitat during mild environ- mental conditions and constricted habitat use when physico-chemical conditions were potentially stressful. Species associations were also transitory; no species pairs consistently exhibited strong spatial overlap. Habitat partitioning thus ap- pears less structured in this stream than in more stable environments that have been studied. The fish fauna was characterized by ecologic plasticity, with the most successful species showing marked habitat flexibility. The South Canadian River in central Oklahoma, like many rivers of the southern Great Plains, is wide and shallow, with seasonal extremes of discharge. Hefley (1937) described the stream thusly: Probably no more ecologically dynamic region exists: the seasonal, diurnal, and yearly fluctuations of meteorological factors are great and sudden; the course of the river changes with each succeeding rain and the shifting sand . . . is constantly being moved by wind and water. In such a stream, physico-chemical variables like temp- erature, salinity, and dissolved oxygen fluctuate widely, and may limit the fish fauna (Echelle et al. 1972; Matthews and Maness, in press), or strongly influence microhabitat selection by fishes (Mat-

Variation in the Plains Minnow, Hybognathus placitus Girard

1856. Hybognathus placitus Girard, Proc. Acad. Nat. Sci. Philadelphia, 8:182. 1856. Hybognathus evansi Girard, Proc. Acad. Nat. Sci. Philadelphia, 8:182. (Has line priority over H. placitus, but first reviser, Jordan and Gilbert, Bull. U. S. Nat. Mus., 16:157, 1882, used H. placitus.) 1932. Hybognathus churchilli Hildebrand, Jour. Washington Acad. Sci., 22: 257. Type.-Five syntypes, USNM 89 (3), MCZ 1789 (1), and ANSP 5065 (1), from the Arkansas River six to eight miles west of Dodge City, Ford County, Kansas. (See also p. 160). Distribution.-Known certainly from Wyoming and South Dakota south to Texas, and east to Missouri (see also p. 162 and Fig. 1). Diagnosis.-Posterior process of basioccipital bone straight, thickened medially, and narrow posteriorly; scale-rows below lateral line 12-21 (15 or more in 93 per cent of specimens examined); diameter of eye less than 1/5 of length of head in adults. Methods.-Standard length and six counts (number of rays in the pectoral and anal fins, number of scales in the lateral-line series, scalerows below and above the lateral line, and number of vertebrae) were taken (Tables 1-6). The measurement and counts were made as described by Hubbs and Lagler (1958:19-26), with the exception of the count of scale-rows above and below the lateral line. Scale-rows above the lateral line were counted over the crest of the back, with one row of scales between the row counted and the origin of the dorsal fin. Scale-rows below the lateral line were counted around the belly, utilizing the second

The Weberian Apparatus of Hybognathus placitus and H. nuchalis (Cyprinidae)

The Weberian apparatus of Hybognathus placitus is described and compared with that of H. nuchalis. Although considerable variation in the Weberian components was observed, the many differences indicate that full specific rank should be retained for both Hybognathus placitus and H. nuchalis. The lateral proc- esses of the first and second vertebrae are regarded as modified ventral ribs. The ascending processes of the scaphium and intercalarium are believed to be homologous to postzygapophyses. The pit into which the articulating process of the scaphium fits is regarded as homologous to those accommodating the third neural pedicle and fourth neural arch. The neural complex is probably composed of the third neural spine plus interspinous bones. The os suspensorium is part of the fourth pleural rib. The most conspicuous difference between these species involves the shape of the pharyngeal process of the basioccipital and the muscles inserted on it. Hybognathus placitus Girard and Hybognathus nuchalis Agassiz present some taxonomic difficulty, but have long been regarded as dis- tinct species. Bailey (1956) concluded that environmental variations, at the time of early development, are translated into structural dif- ferences that can be perceived throughout the life of the fish. He con- sidered both H. Nuchalis and H. placitus as phenotypes of H. nuchalis. The purpose of this study was to test this hypothesis, using the mor- phology of the Weberian apparatus. The Weberian apparatus was named in honor of the discoverer, E. J. Weber, by Bridge and Haddon (1889). Since Weber used nomencla- ture as applied to the ossicles of the mammalian middle ear, not homol- ogous with those of fishes, Bridge and Haddon proposed the nomen- clature currently used. Readers interested in the literature pertinent to the morphology and embryonic development of the Weberian ap- paratus should consult the works of Evans (1924-1925), Watson, (1939), Krumholz (1943), Nelson (1948), 1949, 1955), and Butler (1960). Materials for this study were from a large part of the ranges of the two species, from the Rio Grande to the Missouri River Basin in South Dakota and Montana. We are indebted to Dr. R. M. Bailey, of the 1 Contribution from the Research Foundation and No. 344 from the Zoology De- partment, Oklahoma State University, with partial support from the National Science Foundation.