Plagopterus Research Articles

Spatio‐temporal analyses show conflicting evidence of the role of an invasive minnow in the decline of an endangered desert fish endemic to the south‐western U.S.A.

Abstract Invasive species are often blamed for the declines of native species, although this is often based on anecdotal or incomplete evidence. In the Virgin River (U.S.A.), the red shiner minnow (Cyprinella lutrensis) has been identified as a major factor in woundfin (Plagopterus argentissimus) decline, a critically endangered endemic minnow. We assessed the evidence for the hypothesis that negative interactions between these two fish drove this decline. We tested three predictions: (1) spatial and temporal patterns were significant predictors of assemblage structure; (2) red shiner would show opposite spatial and temporal patterns to native species; and (3) woundfin would show site‐specific decreases in abundance following red shiner invasion. We used a long‐term (28 years) dataset of fish abundances in the Virgin River at 10 regularly monitored sites to test our predictions. Using principal coordinates of neighbour matrices with redundancy analysis, we tested our first two predictions by identifying the temporal and spatial structure of the fish assemblages and comparing the patterns of native fish species to those of the invasive fish species. To test our third prediction, we used a breakpoint analysis of site‐specific population data to determine if woundfin showed stable populations prior to red shiner invasion, followed by declines after invasion. We found that 42% of variation in fish abundances in the river could be explained by spatial patterns, and 12% by temporal patterns. Red shiner showed opposite spatial and temporal patterns to woundfin (but not to other native species), and abundances of red shiner and woundfin were negatively correlated, yielding correlative evidence of negative interactions between red shiner and woundfin. However, our breakpoint analysis did not show the expected patterns and woundfin declined even in sites that did not experience red shiner invasion pointing to alternate mechanisms of decline such as effects of poor water quality. Our analyses provided correlative but conflicting evidence of red shiner influence on woundfin but were unable to identify a definitive causal mechanism of woundfin decline. We discuss two possible explanations for the contemporary woundfin decline and red shiner invasion: displacement of woundfin via negative interactions, or replacement of woundfin by red shiner in a niche already vacated by woundfin due to environmental or anthropogenic disturbances. This study demonstrates that the dynamics between native and non‐native species may not be straightforward and can be complicated by other factors such as anthropogenic activities and environmental changes. This research highlights that long‐term monitoring is essential to untangling interactions between native and invasive species to develop effective conservation methods that address underlying causes of decline.

CFD analysis of an economizer for heat transfer enhancement using serrated finned tube equipped with variable fin segments

Due to the extensive use of heat exchangers in various daily and industrial applications, the improvement of their performances is of great importance. It is evident from the literature that very limited work has been done in serrated finned tube economizer for heat transfer enhancement and pressure drop performance. This paper deals with the heat transfer improvement and pressure drop performance of helical serrated finned tube bundles in inline bare tube counter cross-flow water tube boiler Economizer, which has larger heat transfer area and higher heat exchange efficiency. Numerical simulation on heat transfer performance is carried out on 116.3 TPH of MCR boiler unit, one tube row with three-row finned tube passes; helically wound fin geometries of partially serrated finned tubes are investigated. A steady-state approach, with two-equation, a k-ε turbulence model is employed to examine the effect of Reynolds number in the range of 8000 to 20000. In this study the conjugate heat transfer is considered for the calculation of the conduction in a solid region is coupled with the calculation of the temperature distribution in the working fluid flowing over or through this solid region. The effect of a number of serrated segmented finned tubes per period on the performance of heat transfer enhancement is also investigated. The computational results fall within the range of values predicted by empirical correlation. The results show that the heat transfer is enhanced by up to 3.53% to 5.14% if the number of segments per period varied from 20 to 50.

A validated CFD model of plain and serrated fin-tube bundles

This work presents a Computational Fluid Dynamics model of helically wound fin tube bundles and demonstrates its predictive capability for thermal-hydraulic performance. A consistent validation against experimental data is given for four different fin tube geometries, two with plain fins and two with serrated fins. Predicted heat transfer and pressure drop data are within, or very close to, the experimental uncertainty, with maximum root mean square errors of 13.8% and 14.4% respectively. The modeled fin temperature distribution is used to evaluate three fin efficiency models, revealing that correction equations can be in significant error for tall plain fins. Three sets of semi-empirical correlations for Nusselt and Euler numbers are also evaluated, showing non-conservative predictions for several of the tested geometries. Results from the study confirm the efficacy of reduced domain modeling, whereby geometric periodicity of the heat exchanger array is exploited to reduce computational cost.

Role of Sex Ratio and Density on Fertilization Success of Intensively Cultured Endangered Woundfin

Abstract Woundfin Plagopterus argentissimus are a small, endangered cyprinid found solely in the Virgin River across Utah, Arizona, and Nevada. As of now, only three facilities culture Woundfin for conservation propagation purposes, but there is growing concern that current extensive culture protocols are not meeting the conservation recovery goals outlined in the Virgin River Resource Management and Recovery Program. The development of alternative rearing methodology, like effective intensive culture conditions, could help increase production to more effectively meet the conservation propagation needs for this species. Our goal was to assess the effect of different sex ratios and fish densities on reproductive success at indoor facilities. We measured fertilization success at three different sex ratios (1:1, 1:3, 1:5; female:male) and three different fish densities (0.05, 0.21, and 0.47 fish/L) in a laboratory setting. Sex ratio did not significantly affect fertilization success (P = 0.73). Fertilization was completely inhibited at a density of 0.05 fish/L, but there was no difference in fertilization success between the two other density treatments (P = 0.92). Our findings suggest that a density greater than 0.05 fish/L and a sex ratio of 1:1, 1:3, or 1:5 will likely enhance fertilization success. The results and conclusions of this paper provide valuable rearing information for the Virgin River Resource Management and Recovery Program and hatchery managers attempting to increase production of Woundfin in an intensive culture setting.

Effects of Ultraviolet-B Radiation on Woundfin Embryos and Larvae with Application to Conservation Propagation

Abstract Endangered woundfin Plagopterus argentissimus embryos and larvae were exposed to artificial ultraviolet-B (UV-B) radiation to directly examine the effects on mortality. The experiment was part of a project assisting the Virgin River Resource Management and Recovery Program's efforts to increase hatchery production of this endangered fish. The UV-B radiation used in this experiment was administered in treatments of 0.060, 0.030, and 0.015 mW/cm2 to simulate 100, 50, and 25% of the ambient irradiance levels documented in outdoor tanks and living streams at Bubbling Ponds State Fish Hatchery, in Arizona. Embryos and larvae were exposed for 14.5 h followed by 9.5 h of darkness, in correspondence with the daylight hours at Bubbling Ponds. No embryos survived UV-B treatments; mortality among control (UV-B–free) treatments varied (5–100%) among females, indicating that there may be important parental effects that influence embryo mortality. Larval mortality was also 100% for individuals exposed to any of the three UV-B treatments. In contrast to embryo trials, larval mortality in UV-B–free treatments approached 20% for 2-d-old larvae. These experiments provide evidence that woundfin embryos and larvae are sensitive to even low levels of UV-B when exposed for 14.5 h. Susceptibility of larvae to UV-B also appears to be a function of age at exposure, with older larvae exhibiting significantly lower levels of mortality during the initial days of exposure. Experiments with UV-B mitigation strategies indicated that shade cloth, Aquashade®, and elevated dissolved organic carbon can aid in the attenuation of UV-B, and these strategies may assist hatchery managers in implementing UV-B mitigation measures during periods when woundfin are most susceptible.

Cannibalism of Embryos and Larvae by Adult Woundfin in Intensive Culture: Application to Conservation Propagation

Abstract Woundfin Plagopterus argentissimus are a small, endangered cyprinid native to the Colorado River basin. Woundfin occur only in the Virgin River in Utah, Arizona, and Nevada, and habitat degradation and competition with invasive species threaten their survival. Three facilities raise woundfin in captivity for use in conservation propagation projects. A suspected limiting factor to pond culture production of woundfin is cannibalistic predation on embryos and larvae. We experimentally measured rates of predation on embryos and larvae by adult woundfin at the Bozeman Fish Technology Center in Montana. Predation was a significant source of mortality on both embryos (W = 210, P < 0.001) and larvae (W = 45, P = 0.004). These rates of predation could translate into the loss of thousands of fish over the course of a spawning season at the conservation propagation facilities. We recommend removing embryos from spawning ponds and rearing them in separate tanks or ponds to reduce predation loss.

Evaluation of Woundfin Augmentation Efforts in the Virgin River by Estimation of Admixture Proportions

AbstractThe woundfin Plagopterus argentissimus is imperiled as a result of habitat destruction, water diversion, and the introduction of nonnative species. Augmentation of wild woundfin populations in the Utah portion of the Virgin River with fish from Dexter National Fish Hatchery and Technology Center (Dexter Hatchery) began in 2003. We used 10 microsatellite DNA loci to determine whether captive woundfins are contributing to recruitment in the Virgin River. Admixture analyses based on moment estimators, maximum likelihood, frequency, and Bayesian approaches indicated that the genetic contribution of Dexter Hatchery's woundfin augmentation stocking to 2005 recruitment in the Virgin River was 35–46% in the Washington Fields Diversion reach and 43–59% in the area of the Quail Creek Reservoir inflow. Salvaged wild parental stock was mixed with the captive broodstock at Dexter Hatchery in 2004 and had a genetic contribution of 26–49% to the offspring reared at Dexter Hatchery in 2005. Care must be taken to ensure the genetic integrity of stocked fish as the potential impact on the augmented population can be substantial. These results demonstrate that genetic markers used to infer gene flow (via admixture analysis) from the captive population to the wild population can be applied to determine the effectiveness of hatchery propagation programs and to monitor genetic similarity between wild and stocked fish.

Genetic Characterization of Variation in Captive and Wild Woundfin

AbstractThe woundfin Plagopterus argentissimus is an endangered species that has been extirpated from most of its historic range in the Colorado River basin, now occurring only in the main‐stem Virgin River. In 1987, refugial stocks were established at the Dexter National Fish Hatchery and Technology Center (Dexter) as a hedge against extinction. Offspring from the captive populations have been released in the Virgin River since 1993, by which time wild populations had markedly declined. This study was conducted to determine whether the stocks at Dexter have retained the character of the wild donor stocks as indicated by the distribution of genetic variation within and between stocks. The genetic composition of captive populations may diverge from that of wild donor populations, even over relatively short time periods, owing to founder effect, genetic drift, and selection for traits that are advantageous in captivity. Captive and wild stocks were surveyed, both spatially and temporally, using 10 microsatellite markers developed at Dexter. Microsatellite markers are considered selectively neutral, and this study measured genetic changes due to random evolutionary processes (given our approach, it would be unlikely to identify changes at nonneutral loci due to selection). Overall, the woundfin exhibited high levels of genetic variation for a freshwater species. The samples from the captive and wild woundfin populations had similar levels of heterozygosity, but generally the captive populations had fewer alleles. A comparison of composite samples of captive stocks and recent wild stocks yielded an FST value of 0.004. Although statistically significant, this level of genetic distance is typical of well‐mixed or undifferentiated stocks. After 20 years of captive propagation, the stocks at Dexter do not appear to have been impacted by founder effect or genetic drift.

Twelve microsatellite markers developed in woundfin (Plagopterus argentissimus), an endangered warmwater fish of the lower Colorado River basin

AbstractWoundfin (Plagopterus argentissimus) is one of several endangered warmwater fishes once common to the lower Colorado River basin. Dexter National Fish Hatchery & Technology Center maintains a refugium stock founded in 1982, and augmented with c. 1000 young fish in 1989. Genetic characterization of the refugium stock and salvaged fish from the Virgin River is necessary to develop a strategy to incorporate salvaged fish into the hatchery stock. We developed an enriched microsatellite library and 12 species‐specific polymorphic loci. Alleles per locus ranged from 10 to 19, averaging 13. The average expected and observed heterozygosities were 0.884 and 0.895, respectively.

RTD studies in a falling film graphite evaporator with internal spiral fins: Influence of the geometry

AbstractA hydrodynamic study of a new graphite evaporator has been performed. In this exchanger the fluid flows as a thin film on a spirally wound fin which forms a spiral staircase inside a tube. The slope θm of the spirally wound fin is modifiable. The residence time distribution (RTD) of the film was measured for different fin slopes θm and several film flowrates mf. The flow pattern was then modelled thanks to the DTS software as a cascade of perfect mixed cells and the mean residence time τm was calculated. The evolution of τm as a function of θm and mf is accurately represented by a power law relation.

Diel food utilization by woundfin, Plagopterus argentissimus, in Virgin River, Arizona

Woundfin, Plagopterus argentissimus, fed predominantly on simuliid larvae during the day, and shifted to the larger Hydropsyche spp. at night. Ephemeropteran larvae were eaten nearly uniformly throughout the 24 hour period. Mean weight of food consumed varied from 20–40 mg per individual (0.7–2.5% body weight) throughout the 24 h period. Our estimated daily ration of about 8% body weight, at temperatures that varied between 15–25°C, is based upon our measure of mean gut contents over a 24h period, combined with intestinal evacuation rates suggested for other cyprinids in the literature. The relatively continuous feeding pattern suggests a foraging strategy that would minimize competition with other species for food during June, a period of minimum annual food abundance in Virgin River.

New Host Records for the Asian Fish Tapeworm, Bothriocephalus acheilognathi, in Endangered Fish Species from the Virgin River, Utah, Nevada, and Arizona

Bothriocephalus acheilognathi has been considered one of the most dangerous pseudophyllidean cestodes for cultured carp in Europe. This species, first described from fish in Japan, is common in the intestine of young grass carp cultured in South China. From China, cestode infections have followed grass carp imports into Europe, Russia, and the United States (Hoffman and Schubert, 1984, In Distribution, biology, and management of exotic fishes, Courtnay and Stauffer (eds.), Johns Hopkins University Press, Baltimore, pp. 233-261). To date there have been no published records of B. acheilognathi in the fishes found in the Virgin River of Utah, Nevada, and Arizona. During a preliminary survey of parasites of Plagopterus argentissimus and other endangered fish species from the Virgin River near St. George, Utah, 18% of 17 Gila robusta seminuda examined were found to be infected with the B. acheilognathi. From the same site no P. argentissimus (192) (number checked for parasites in paren-

Ecological Distribution of Fishes of Moapa (Muddy) River in Clark County, Nevada

Abstract Fish collections were made at nine stations along the Moapa River of southern Nevada. Four native species are ecologically separated into headwater and middle-stream types. The headwater fishes are ecologically segregated into one pond species (Crenichthys baileyi) and one stream species (Moapa coriacea). The apparent temperature preference for both species is near 29.5 C. Temperature range for Crenichthys is 27–32 C and for Moapa 19.5–32 C. Both Gila robusta and Rhinichthys osculus are most abundant in the turbid middle portion of the stream in undisturbed, deep riffle habitats. A fifth native species, Plagopterus argentissimus, is extremely rare or of accidental occurrence. The unsaturated Moapa River environment has been easily colonized by exotic or non-native species, most recently and most successfully by Poecilia mexicana. An additional species, Gambusia affinis, is widespread and abundant throughout much of the stream. Cyprinus carpio, Notropis lutrensis, Pimephales promelas, Ictalurus me...