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As precipitation and temperature patterns change, the resulting alterations in hydrologic conditions may adversely affect some stream fishes. The unique guild of freshwater, pelagic broadcast-spawning minnows found in the western United States appears to be particularly sensitive to low-flow conditions. We examined reproductive and recruitment patterns of one of these species, Rio Grande silvery minnow (Hybognathus amarus), over a three-year period, which included one year of extreme drought. We followed gonadal development from March through September each year, from 2017 to 2019, to determine if Rio Grande silvery minnow were reproductively active during extreme drought. The population structure was also monitored to confirm successful recruitment over the same period. We found that in all years Rio Grande silvery minnow were reproductively active in April through early June, including during extreme drought in 2018. However, almost no recruitment occurred in 2018, and by early 2019 the population was dominated by older, wild age-2 fish and hatchery-reared fishes. Our work supports previous research on pelagic broadcast-spawning minnows and confirms that extreme low-flows results in near-complete recruitment failure of Rio Grande silvery minnow. This work will help inform management and conservation of Rio Grande silvery minnow and other pelagic broadcast-spawning minnows during drought or low flows years.

Gila elegans, Hybognathus amarus, and Tiaroga cobitis (Family Cyprinidae, Order Cypriniformes) are endemic and endangered fishes in the southwestern United States. We present complete mitochondrial genomes for each species. Each mitochondrion consisted of 13 protein-coding genes, 2 ribosomal (rRNA) genes, 22 transfer RNA (tRNA) genes, and a single control region (D-loop), and gene order was consistent with other cyprinid fishes. Total genome lengths were 16,593 base pairs (bp) for G. elegans, 16,705 bp for H. amarus, and 16,802 for T. cobitis. The GC content in G. elegans and H. amarus was 44%, but higher in T. cobitis at 48%. Phylogenetic trees were generated to confirm relationships inferred via novel mitogenomes, and best-supported trees were consistent with previous research.

Streamflow intermittency can reshape fish assemblages and present challenges to recovery of imperiled species. During streamflow intermittency, fish can be subjected to a variety of stressors, including exposure to crowding, high water temperatures, and low dissolved oxygen, resulting in sublethal effects or mortality. Rescue of fishes is often used as a conservation tool to mitigate the negative impacts of streamflow intermittency. The effectiveness of such actions is rarely evaluated. Here, we use multi-year water quality data collected from isolated pools during rescue of Rio Grande silvery minnow Hybognathus amarus, an endangered minnow. We examined seasonal and diel water quality patterns to determine if fishes are exposed to sublethal and critical water temperatures or dissolved oxygen concentrations during streamflow intermittency. Further, we determined survival of rescued Rio Grande silvery minnow for 3&ndash, 5 weeks post-rescue. We found that isolated pool temperatures were much warmer (&gt, 40 &deg, C in some pools) compared to upstream perennial flows, and had larger diel fluctuations, &gt, 10 &deg, C compared to ~5 &deg, C, and many pools had critically low dissolved oxygen concentrations. Survival of fish rescued from isolated pools during warmer months was &lt, 10%. Reactive conservation actions such as fish rescue are often costly, and in the case of Rio Grande silvery minnow, likely ineffective. Effective conservation of fishes threatened by streamflow intermittency should focus on restoring natural flow regimes that restore the natural processes under which fishes evolved.

A major reason why conservation aquaculture is needed to improve the success of aquaculture-assisted fisheries is that traditional production aquaculture produces fish with mal-adaptive behaviors. These behaviors can be produced via domestication and culture techniques, and preventing these mal-adaptive behaviors requires integrating improvements in genetic management and culture protocols. The genetic protocols needed to minimize hatchery-induced genetic changes have received considerable attention, but changing the way fish are raised has received less effort. Conservation aquaculture cultures fish in environments that resemble their native habitats so that when stocked, they behave like wild fish rather than hatchery fish. A purpose built-conservation aquaculture facility can also be used to learn about a species’ behavior and how it reacts to changes in the environment, something which can be difficult or expensive to study in the wild. These observations can then be used to help direct both propagation and recovery management. This paper provides the rationale for why genetic management, culture systems, and management practices need to be altered to produce fish that are behaviorally similar to wild fish for aquaculture-assisted fisheries programs. It then provides a description of some of the behaviors of the endangered Rio Grande silvery minnow Hybognathus amarus that were observed at the Los Lunas Silvery Minnow Refugium, a purpose-built conservation aquaculture facility, and explains how some of these behaviors can be used in culture and recovery management. Behaviors described are: schooling; predator avoidance; feeding behavior; use of vegetation for cover and predator avoidance; habitat use by bottom substrate; location in the water column; upstream movement via a fish ladder; movement upstream in a high-velocity channel; response to changes in water level; spawning behavior; seine avoidance; and Kaah-chee-nyee Srkaash, a behavior described for the first time.

Federally endangered Rio Grande Silvery Minnows (RGSM; Hybognathus amarus) were raised in one of three culture regimes: intensively, with only a hatchery diet; semi-intensively with access to natural food and hatchery diet supplementation; and with only natural food available at the Los Lunas Silvery Minnow Refugium (Los Lunas, New Mexico), a naturalized conservation refugium designed to mimic the natural environment of the RGSM in the Rio Grande. The project compared each culture regime and assessed differences and similarities in lipid and fatty acid content between feeding an artificial diet and consumption of natural food items in this species. After 117 d, whole-body lipid levels and fatty acid profiles were measured in each group and compared with values for wild RGSM. Fish fed the hatchery diet exclusively or as supplementary feed had significantly higher percent lipid (15.5% ± 0.5% and 10.6% ± 0.1%, respectively) than fish raised without access to the diet. Both groups had significantly higher percent lipid than fish raised in the refugium or wild fish (8.3% ± 0.1% and 7.8% ± 0.2%, respectively). Condition factor differed among groups and was highest in fish fed the hatchery diet (1.00) followed by fish supplemented with the hatchery diet (0.93), refugium fish (0.91), and wild fish (0.90). In this respect, refugium fish appeared more similar to wild fish than fish fed the hatchery diet or offered the diet as a supplement. Comparison of fatty acid profiles among groups showed marked differences among wild fish, refugium fish, and those fed the hatchery diet, either exclusively or as supplementary feed. Total omega-3 fatty acids, expressed as percentage of total fatty acids, were highest in wild fish but similar among other groups. Total omega-6 fatty acids showed an opposite trend, with five to nine times higher percentages of linoleic acid observed among fish from the three culture regimes compared with wild fish. Significant differences in lipid content and fatty acid composition between wild RGSM and cultured silvery minnows reflected their respective diets and culture regimes. Given similarities in fat content and condition factor with wild RGSM, we conclude that fish in the refugium do not require supplemental feeding with an artificial diet for this type of naturalized conservation management. Results from this study show that RGSM readily forage on natural food items present and also artificial feed when available, indicating dietary plasticity, which is advantageous for fish culture and future recovery.

The lower lethal temperature of the endangered Rio Grande silvery minnow, Hybognathus amarus, was estimated from survival rates of fish overwintered in above-ground tanks. Temperature went to 0.0°C both winters. In 2012–2013, survival of Age class 0 fish was 79.87%, and in 2013–2014, survival of Age class 1 fish was 97.1%, suggesting that if Rio Grande silvery minnow is subjected to seasonal temperature changes, lower lethal temperature is ≤0.0°C. Results show that heating hatchery water in the winter is unnecessary. Additionally, current management guidelines that preclude reintroduction of the species into river sections where winter temperatures are ≤1°C must be reevaluated.

Habitat fragmentation and changes in flow regime can structure fish assemblages, resulting in extirpations or invasions. A guild of freshwater stream fishes that spawn semi-buoyant, nonadhesive eggs directly in the water column are particularly susceptible to extirpation in fragmented streams. The pelagic broadcast-spawning Rio Grande Silvery Minnow Hybognathus amarus was listed as endangered in 1994 and has been intensely managed since. I used mean May flows and the number of times the channel dried within a year to predict numbers of Rio Grande Silvery Minnow captured in isolated pools in the Middle Rio Grande, New Mexico. Adult Rio Grande Silvery Minnow numbers increased as previous year’s mean May discharge increased, and generally decreased with each subsequent drying event. Similarly, numbers of young-of-year Rio Grande Silvery Minnow increased with increasing mean May discharge in the current year. However, young-of-year minnow were either very abundant or nearly absent in isolated pools, d...

The Yellowstone River is the longest unimpounded river in the conterminous United States. It has a relatively natural flow regime, which helps maintain diverse habitats and fish assemblages uncommon in large rivers elsewhere. The lower Yellowstone River was thought to support a diverse nongame fish assemblage including several species of special concern. However, comprehensive data on the small nongame fish assemblage of the lower Yellowstone River is lacking. Therefore, we sampled the Yellowstone River downstream of its confluence with the Clark’s Fork using fyke nets and otter trawls to assess distributions and abundances of small nongame fishes. We captured 42 species (24 native and 18 nonnative) in the lower Yellowstone River with fyke nets. Native species constituted over 99% of the catch. Emerald shiners Notropis atherinoides, western silvery minnows Hybognathus argyritis, flathead chubs Platygobio gracilis, sand shiners Notropis stramineus, and longnose dace Rhinichthys cataractae composed...

Surveys based on nonrandom site selection, or convenience samples, are often a necessary part of large-scale monitoring programs to help minimize costs. The reliability of convenience samples to inform managers about distributions or population status of imperiled species is questionable, however, because the samples may not be representative of the whole population. We compared fish community data from 20 nonrandom, long-term monitoring sites for Rio Grande Silvery Minnow Hybognathus amarus with those from 20 randomly chosen samples collected during two surveys (one in summer, one in autumn) in the Rio Grande, New Mexico. We compared the species richness, community composition, and the catch per unit effort (CPUE). Fish species compositions, which were similar between both sets of summer and autumn surveys, were nearly identical in the autumn surveys. Similarly, we found consistent Rio Grande Silvery Minnow CPUE between surveys; summer random surveys estimated 0.32 fish/100 m2 sampled, whereas su...

To elucidate feeding kinematics of the endangered Rio Grande silvery minnow (Hybognathus amarus), high-speed (500 frames/s) recordings of dorsal, lateral, and ventral feeding of larval silvery minnow were analyzed through National Institute of Health ImageJ software. Suction-feeding with buccal expansion was observed when feeding was apparent, and approach and feeding angle of H. amarus approaching the feeding substrate were calculated. Angles of approach averaged ca. 24–90°, while feeding angles were ca. 90°. Duration and touches, duration and bites, and touches and bites were correlated at 0.74, 0.62, and 0.54, respectively. Video analysis of feeding kinematics showed that H. amarus uses a combination of biting into the substrate followed by rapid lateral movement of the head. Hybognathus amarus has evolved a rapid-feeding mechanism in a turbid environment that allows for tasting and feeding sequences averaging 50–80 milliseconds.

The endangered Rio Grande silvery minnow Hybognathus amarus was cultured in 2.44-m-diameter outdoor tanks in a 131-day yield trial to assess growth, survival, and percentage of taggable-sized fish ( >35 mm total length) when stocked at 500/tank (1.07 million/ha), 1,000/tank (2.14 million/ha), and 1,500/tank (3.21 million/ha). At harvest, fish averaged 45.6 mm and 0.94 g in the 500/tank treatment, 42.6 mm and 0.74 g in the 1,000/tank treatment, and 38.4 mm and 0.55 g in the 1,500/tank treatment; the differences were significant ( P = 0.05). Survival in the three treatments was 70%, 64%, and 52%, respectively, but the differences were not significant. Percent taggable-sized fish was 86%, 89%, and 65%, respectively, but the differences were not significant. Yield was 672.5 kg/ha, 1,026.6 kg/ha, and 887.8 kg/ha, respectively; yield in the 1,000/tank treatment was significantly greater than that in the 500/tank treatment, but was not significantly greater than that of the 1,500/tank treatment. This facility is a conservation facility and a major goal is to raise fish without formulated feed. Fertilization produced good growth for the first month, but little growth occurred during the second month so supplemental feed had to be used for the final 60 d of the yield trial.

We designed a study to determine if Rio Grande silvery minnow Hybognathus amarus, an endangered species, would use an instream, rock channel fishway on the Rio Grande near Albuquerque, New Mexico. We implanted 6,657 Rio Grande silvery minnow with passive integrated transponders and used a passive scanning station with two antennas located within the fishway to document movements from seven release locations, up to 19.7 km upstream and 13.5 km downstream of the diversion dam. Between 11 March and 21 August 2011, 243 individuals were detected (3.7% of all fish released), with 74.1% fish being detected from upstream release sites and 25.9% from downstream release sites. We determined 14 Rio Grande silvery minnow successfully ascended the fishway, and an additional 20 fish from downstream release locations were detected on the upstream antenna only, inferring passage. We conclude Rio Grande silvery minnow can use appropriately constructed fishways. Received October 17, 2011; accepted March 21, 2012

Assessments of the assumptions underlying catch-per-unit-effort (CPUE) data are necessary to determine whether catch data provide a reliable relative abundance metric. Rio Grande silvery minnow Hybognathus amarus were collected with fyke nets from seasonally flooded habitats of the Rio Grande in New Mexico to determine habitat use by the species during spring runoff in May and June of 2008 and 2009. The CPUE was calculated as fish/h to assess relative abundance among sites and sampling dates due to differences between the durations of the samples in 2008 and 2009. The assumption that the number of fish captured with fyke nets is proportional to effort was assessed by using a multiple-regression model. Catch per unit effort was also compared over the course of a day to determine whether diel differences in catch rate exist. Catch of Rio Grande silvery minnow increased with fyke-net soak time during 2008 and 2009; however, the proportion of the variability explained by the model was greater for 200...

The Middle Rio Grande (MRG) of New Mexico has been influenced by man for over 500 years. Native Americans began diverting water to irrigate agricultural crops in the floodplain in the 14th century. The Spanish followed and increased agricultural irrigation to over 125 000 acres. Frequent flooding of the MRG valley in the 19th century led to many engineering projects in the early 20th century to control flooding. A series of impoundment dams, diversion dams, and levees were constructed. The loss of floodplain habitats throughout the MRG Valley has altered the riparian community and caused the demise of many fish species. A controlled flood pulse from Cochiti Reservoir, New Mexico was initiated in April 2005 to support the recovery of the endangered Rio Grande silvery minnow, Hybognathus amarus. This study documents habitat selection by larval fishes in a restored floodplain in the Rio Grande, NM. Larval fish light traps captured 394 larvae representing four cyprinid species (Pimephales promelas, H. amarus, Cyprinella lutrensis and Cyprinus carpio). Results for CCA indicate that Hybognathus amarus prefer shallow, low velocity habitats. Results from Chao-Jaccard similarity index indicated that relative contribution was highest in P. promelas at 64% followed by H. amarus 33%. Results from (dis)similarity analysis reveal that species composition between habitat orientation and date was highest in H. amarus at 42% followed by P. promelas 40%. Cyprinella lutrensis and C. carpio represented 9.5 and 8.5%, respectively. A general linear model indicated that only depth and velocity were significantly different (p = 0.02 and p = 0.03 respectively).

This article describes the initial season‐long yield trial of raising the endangered Rio Grande silvery minnow, Hybognathus amarus, in the conservation rearing facility at the Los Lunas Silvery Minnow Refugium. Ten thousand fish (90,900/ha) were stocked on June 22, 2010. Production was based on a total of 653 mL (5.936 L/ha) of 11‐37‐0 N‐P‐K and 5.5 kg (50 kg/ha) of alfalfa pellets. Fish were harvested in October; almost all were harvested 18–27 October. At stocking, fish averaged 21.7 mm total length and mean weight was 0.10 g. At harvest, fish averaged 48.98 mm and 1.12 g. Fish were sampled monthly, and increased lengths and weights through the study were significant (P = 0.05). Five thousand eight hundred ninety‐two fish were harvested (58.92% survival). Yield was 59.99 kg/ha. Temperature, dissolved oxygen (DO), pH, un‐ionized ammonia, nitrite, turbidity, alkalinity, and chloride were measured at seven sites throughout the outdoor refugium. Secchi disc visibility was measured in the stream and in the ponds. Only two variables (DO and pH) went outside permitted values, but were easily corrected. Harvest was difficult due to the many different naturalized areas consisting of varying depths, channel widths, and substrates.

The Los Lunas Silvery Minnow Refugium is a conservation fish hatchery that produces the endangered Rio Grande silvery minnow ( Hybognathus amarus Girard [Cyprinidae]). The major management goal of a conservation fish hatchery is to raise fish in a naturalized environment that is similar to their native ecosystem, including native vegetation. This is diametrically opposed to management at traditional fish hatcheries, where rooted plants in fish culture units are considered to be weeds because they can cause management problems; most notably, these plants interfere with fish harvest. Fifteen native wetland and 8 native upland species of plants were installed in the naturalized outdoor conservation fish-rearing facility. The plants were used to produce shade, shelter from predators, places for food to colonize, areas of low-velocity water, and to create riparian overbank areas that could be inundated in order to simulate floodplains along the Rio Grande. The plants have thrived at the facility. Continuous manual weeding is required from March to October to remove weeds and to keep sedges and rushes from filling the ponds. Observations indicate that the plants are achieving the intended purposes.

A screening-level ecological risk assessment was applied to two extensive, but previously unanalyzed datasets from the middle Rio Grande (MRG) in New Mexico. The assessment evaluated how adverse water-quality effects from aquatic toxicants may have influenced the population decline of the endangered Rio Grande silvery minnow (Hybognathus amarus; silvery minnow). Standardized US Environmental Protection Agency (USEPA) screening-level ecological risk assessment procedures were applied to chemicals assessed in samples collected from the MRG between 1985 and 2003. Since more chemicals have established risk-screening criteria, relative to water-quality criteria, this approach produces more complete assessments. Chemical concentrations at some locations and times were potentially sufficient to affect fish health or produce localized mortalities. Many constituents displaying the highest risks have substantial natural sources within the watershed; native species likely would have adapted to natural instream concentrations such that actual risks might be markedly less than projected by a risk screening based on generic aquatic-life criteria. Also, highest risks found for individual and combinations of contaminants were very inconsistent both within and across the sites. As such, this risk assessment does not support the conclusion that toxicants were a primary factor causing the silvery minnow population to decline in the MRG between 1985 and 2003. The assessment indicates that sediment-borne, relative to water-borne, contaminants appeared to present the greatest risks to the silvery minnow and thus should have increased focus during future assessments of potential contaminant effects in the MRG. Contaminants of greatest concern are identified. This study presents approaches to cost-effectively assess and reduce uncertainties associated with potential water quality effects, and to help direct future assessments of water quality onto those contaminants likely to produce potentially significant effects. The techniques presented and criteria compiled are suitable for aiding similar assessments in other aquatic habitats.

Long-distance drift of eggs and larvae has been identified as a possible cause of downstream displacement and poor recruitment of the endangered Rio Grande silvery minnow (Hybognathus amarus; silvery minnow). Seven experiments were conducted using artificial eggs to estimate silvery minnow egg drift and retention in the Albuquerque and Isleta reaches of the regulated Middle Rio Grande, New Mexico, USA over a range of flows during expected spawning times. Bead retention varied by reach, discharge, and shape of the hydrograph. Highest retention (6.9 and 9.7% per km in the Albuquerque and Isleta reaches, respectively) occurred on the ascending limb of a high flow in areas where there was substantial floodplain inundation. Retention was maximized at different flows in each reach (97 and 140 m3/s, respectively), possibly associated with reach-specific floodplain inundation thresholds. Lowest retention in each reach (2.1 and 1.7%, respectively) occurred on the descending limb of low and high flows, respectively. Of the silvery minnow eggs produced in the combined Albuquerque and Isleta reaches in 2005, 8–14% are predicted to have been retained in the Albuquerque Reach (67 km) and 49–83% in the Isleta Reach (86 km) based on the distribution of adult fish and measured bead retention rates. Although silvery minnow propagules are capable of drifting long distances, our study suggests that considerable retention occurs in the Middle Rio Grande. Habitat restoration to increase channel habitat complexity, and flow management to promote floodplain inundation should help to retain a greater proportion of propagules in upstream reaches. Copyright © 2010 John Wiley & Sons, Ltd.

A non-native population of plains minnow Hybognathus placitus in the Pecos River, New Mexico, USA, replaced the endemic, ecologically similar Rio Grande silvery minnow Hybognathus amarus in less than 10 years. Competitive exclusion is hypothesized as a mechanism of replacement. The following evidence was examined for potential support: (1) the historical population trend of H. amarus versus H. placitus; (2) relative suitability of the modified flow regime for H. amarus versus H. placitus; (3) potential for habitat overlap; and (4) spawning periodicity and body length in the non-native population of H. placitus. Historical data indicate H. amarus did not decline until H. placitus was present, after which it disappeared rapidly and H. placitus proliferated. The natural flow regime of the Pecos River was changed via base-flow reductions and capture of springsnowmelt runoff, making it similar to flow regimes associated with likely source populations of non-native H. placitus. Spring runoff is an important spawning cue for H. amarus, but not H. placitus and H. placitus appears to be naturally more tolerant of diminished streamflow. Extant H. placitus were associated with a relatively pristine river reach that was most likely the stronghold for the replaced H. amarus population. Given high ecological similarity, habitat overlap was likely high during the period of replacement. Hybognathus placitus in the Pecos River had a protracted spawning season (April through September), whereas extant H. amarus in the Rio Grande had a short spawning season (a few days in May or June during snowmelt runoff). Most H. amarus die after their first spawning season and few exceed 60 mm standard length (SL), whereas quite a few H. placitus survive at least until their second spawning season and exceed 60 mm SL. Co-occurrence of multiple spawning cohorts may stabilize annual reproductive output of H. placitus and larger individuals may be more fecund and produce larger eggs that survive better. Spawning flexibility, greater size, and higher environmental tolerance likely gave H. placitus a reproductive and survival advantage over H. amarus, consistent with a deterministic pattern of rapid species replacements in the plains, in which tolerant, competitive species from the Red River drainage or Gulf of Mexico coast rapidly replace more sensitive, endemic congeners in disturbed, remnant habitats.

Pelagic-broadcast spawning minnows are a reproductive guild of fishes, of which several species occur in the American Great Plains and Southwest. The eggs and larvae of these species drift laterally and downstream, with drift distances varying depending on channel conditions and flow. Persistence or recolonization of these species in upstream reaches must depend on retention of eggs and larvae or upstream dispersal of later life stages, otherwise net downstream displacement of eggs and larvae would result in upstream extirpations. However, only a few individuals of several species have been observed dispersing. Here, we describe 2 direct visual observations of the young-of-year of 4 species of pelagic-broadcast spawning minnows dispersing upstream en masse. In August 2009, we observed Plains Minnow (Hybognathus placitus), Speckled Chub (Macrhybopsis aestivalis), and Rio Grande Shiner (Notropis jemezanus) dispersing upstream. The continuous shoal of fish was >200 m in length and was dispersing upstream at a rate of >1000 fish/min. In July 2017, we observed a continuous shoal of Rio Grande Silvery Minnow (Hybognathus amarus) approximately 1.9 km in length dispersing upstream at a rate between 350 and 1500 fish/min. While such dispersal events are rarely observed, they may be important for maintenance of populations in upstream areas.

We intensively sampled fishes from two reaches of the Rio Grande within the Albuquerque Basin (Albuquerque and Belen valleys) during 1998–2001, compared our findings with those from 1984, and compiled a list of all fishes known from the two reaches. Structure of assemblages (richness, diversity, abundance distributions–taxon dominance versus rank abundance) was similar between reaches in 1998–2001, but the faunas had low taxonomic similarity. The nonnative white sucker (Catostomus commersonii), western mosquitofish (Gambusia affinis), and native red shiner (Cyprinella lutrensis) dominated the Albuquerque Valley. Faunal change in the Albuquerque Valley between 1984 and 1998–2001 indicated all native fishes besides the red shiner declined, particularly the Rio Grande silvery minnow (Hybognathus amarus) and longnose dace (Rhinichthys cataractae). In contrast, the red shiner alone dominated the Belen Valley, nonnative fishes were less dominant, and aside from the Rio Grande silvery minnow and longnos...

We used a swim chamber, flume, and large-scale fishway models to assess the swimming performance, behavior, and passage success of endangered Rio Grande silvery minnow Hybognathus amarus. Field-captured silvery minnow (53–88 mm total length) swam 114–118 cm/s (i.e., up to 20.9 body lengths/s) in a swim chamber in water temperatures of 15, 19, and 23°C. The relationship between time to fatigue and water velocity showed that endurance declined sharply at velocities above 60 cm/s, a threshold that is consistent with critical swimming speed estimates and may represent a transition from aerobic to anaerobic metabolism. Water temperature and fish length were positively correlated with swimming performance. At water velocities of 60 cm/s and less, silvery minnow routinely swam the equivalent of 50 km (125 km maximum) in a swim chamber in less than 72 h. The proportions of silvery minnow that successfully ascended a flume over sand, gravel, or cobble substrate declined as water velocity increased to 53 c...

Captive propagation of the federally endangered Rio Grande silvery minnow Hybognathus amarus has been identified as essential for the recovery of the species. A starter diet was initially developed for this cyprinid to support rapid growth through the larval stage. The diet, however, was too costly to support the grower phase of the species. A series of trials was conducted to determine whether a grower diet could be developed that would be cost effective while maintaining fish performance. Quadruplicate lots of Rio Grande silvery minnow (approximately 90 d posthatch, 0.39–0.42 g) were fed a reference diet or one of five experimental diets until just before gonadal maturation at two facilities in New Mexico (New Mexico State University [NMSU] and Dexter National Fish Hatchery and Technology Center [Dexter]). The diets varied in percent composition of ingredients to account for a range in feed costs. Cyclop-eeze (Argent, Redmond, Washington), krill, liver, and fish meals were present in the refere...

In an attempt to reestablish populations of Rio Grande silvery minnow Hybognathus amarus within its former range, initiatives were set forth to propagate the species in hatcheries, augment wild populations through repatriation, and rescue the species from isolated and receding pools. Physical stressors associated with these recovery efforts, however, result in stress that increases the vulnerability of the minnow to opportunistic pathogens and predation, possibly decreasing poststocking survival. We assessed the physiological stress response to standard management practices by characterizing the changes in plasma cortisol, glucose, and osmolality. When subjected to the individual stressors of 30 s of handling, 3 h of confinement (density, 100 kg/m3), or 3 h of transport (density, 40 kg/m3), moderate changes in plasma glucose and plasma osmolality were observed during recovery whereas changes in plasma cortisol were not detectable. When fish were subjected to consecutive stressors (30 s of handlin...

We examined contents of alimentary canal from pond-reared Rio Grande silvery minnows (Hybognathus amarus; n = 183) to determine frequency of occurrence for foods consumed among small (9–20 mm), medium (21–35 mm), and large fish (36–75 mm). Among 183 fish, 19% (n = 34) of alimentary canals were empty. Of those with food items (n = 149), insects were the most common and were present in 66% of fish, followed by formulated feed (60%), diatoms (40%), cladocerans (36%), rotifers (35%), filamentous algae (32%), bryozoan statoblasts (19%), copepods (11%), protozoa (9%), plant material (9%), ostracods (6%), detritus (5%), and sand (4%). Among size groups, small and medium fish consumed a greater variety of foods than large fish. Information on contents of alimentary canal of pond-reared Rio Grande silvery minnows will aid in refining culture techniques for this federally listed endangered species.

Rehabilitation of the Middle Rio Grande in central New Mexico has become necessary to mitigate the effects of over a century of water and land development. The primary driving force behind rehabilitation efforts is the federally endangered Rio Grande silvery minnow (Hybognathus amarus). Bendway weirs, erosion control and channel-stabilization structures placed transverse to the channel flow, have been used to prevent river migration while enhancing aquatic habitat. Habitat improvement plans on the Middle Rio Grande include the installation of bendway weirs, but the potential benefits of these structures for Rio Grande silvery minnow are unknown. We conducted a theoretical study on the flow conditions created by bendway weirs to determine if it is possible to create physical habitat for Rio Grande silvery minnow while simultaneously protecting the riverbank. Our study suggested that bendway weir installation could lead to the reduction of downstream displacement of Rio Grande silvery minnow eggs, the creation of Rio Grande silvery minnow feeding and refugia habitat, and the creation of drought or low flow habitat through scour hole formation. We also noted that the weirs could also serve as potential habitat for predators, and suggest further studies to better quantify the possible role of bendway weir installation. Copyright © 2009 John Wiley & Sons, Ltd.

The Rio Grande silvery minnow (Hybognathus amarus) was historically the most abundant fish in the Rio Grande Basin. However, populations have been declining to the point of being listed under the Endangered Species Act. Potential causes for the decline have been studied, yet little attention has been paid to food resources. This study had three objectives: (1) Determine whether larval fish show a substrate preference when foraging. (2) Determine whether larval fish have a diatom preference when presented with 15 diatom species over six feeding trials. (3) I investigated the possibility of training/conditioning H. amarus to feed on natural food sources (diatoms) and observe conditioning response (reaction time to feeding). I found no difference between substrate preference (p = 0.26). Results for feeding trials 1, 2, and 3 revealed a preference for Nitzschia palea (p < 0.01). Trial 4 revealed a preference for N. paleaformis (p < 0.01). Navicula veneta was the preferred diatom species in feeding trial 5. Nitzschia cf. intermedia was preferred in trial 6 (p < 0.03). Results from these feeding trials proved that H. amarus larvae learn quickly and can be trained to feed on diatom cultures after only one 30-min exposure. Pre-conditioned H. amarus arrived at diatoms cultures in 49 sec ± 39 sec compared to non-conditioned H. amarus, which arrived at diatom cultures at 250 sec ± 550 sec.

Uniquely tagged animals provide an opportunity to study changes in population demographics and movement. Passive integrated transponder (PIT) tags are used to monitor growth, movement, and survival of fishes. Laboratory studies of tag retention and mortality in small-bodied, warmwater cyprinids after insertion of PIT tags are rare. Mortality induced by two PIT tag implantation methods was compared, and tag retention after implantation was assessed. Relations between standard length and tag retention and between standard length and survival in Rio Grande silvery minnow Hybognathus amarus were examined. Fish were randomly selected and PIT-tagged with 12.5-mm tags via surgical incision or needle injection and were held in laboratory aquaria for 32 d. Mean (±SE) survival on day 32 was 99 ± 1% for control fish, 87 ± 6% for fish that received tags by incision, and 50 ± 5% for fish that received tags by injection. We also tagged 280 fish by incision and held them in aquaria for 49 d. On day 49, survival...

Diatoms consumed by Rio Grande silvery minnows (Hybognathus amarus) collected 104 years apart were used to deduce ecological requirements of this endangered species and to infer a possible cause of its decline based on environmental conditions in the Rio Grande. In 1874, foraged diatoms were largely motile, silt tolerant generalist and epipelic species (e.g. Navicula capitatoradiata, Navicula cryptotenella, Nitzschia palea, Sellaphora pupula) somewhat tolerant to pollution and indicative of eutrophic conditions, low dissolved oxygen, and high biological oxygen demand (BOD). In contrast, diatoms foraged in 1978 were mainly nonmotile epipsammic species (Fragilariaceae) sensitive to pollution and characteristic of low nutrient, oligotrophic conditions with high dissolved oxygen and low BOD. The large-scale difference in composition of the foraged diatom assemblages is consistent with a decline in nutrients and a shift in trophic state commonly associated with river regulation by dams. The results suggest that facilitating allochthonous input of detritus and nutrients into the Rio Grande ecosystem to meet foraging requirements for algivorous and detritivorous fish species such as H. amarus would be a good river restoration strategy.

The Rio Grande silvery minnow, Hybognathus amarus, is a federally endangered cyprinid now confined to the middle Rio Grande, New Mexico, in a fraction of its former range. The precipitous decline of the remaining wild population and lack of recruitment in the summer of 2000 prompted collection and placement of eggs and wild fish in propagation facilities. The aim of this study was to assess the genetic effects of hatchery propagation in the Rio Grande silvery minnow using 10 microsatellite loci and partial mitochondrial ND4 sequences. Three hatchery stocks (2001, 2002, and 2003) and the wild source population (collected in 2001–2002) were considered. Principal findings were; (i) captively spawned and reared Rio Grande silvery minnow had depleted levels of allelic diversity but similar levels of heterozygosity to the wild population, and (ii) fish raised from wild-caught eggs maintained similar levels of allelic diversity but had higher inbreeding coefficients than the wild source stock. With the repatriat...

The Rio Grande silvery minnow (Hybognathus amarus) was historically an abundant and widespread species in the Rio Grande Basin. Its decline to endangered status had many probable causes and has spanned more than a century. Specimens of H. amarus collected in July 1874 at San Ildefonso, near Santa Fe, New Mexico, allowed a retrospective assessment of the ecology and morphology of the species and the environmental conditions of the Rio Grande in areas foraged by these minnows. Analysis of diatoms from the gut showed that H. amarus foraged mainly in nutrient-enriched areas on mud substrates in 1874 and to lesser extents on periphyton associated with plant, sand, and rock substrates. Gut contents included a considerable amount of fine-grained sediment and a wide variety of organic materials including detritus, pine pollen, cyanobacteria, algae, and diatoms. Scale annuli showed that H. amarus was once a relatively long-lived minnow; all age classes from 1 to 5 were present in 1874. The presence of multiple ind...

A sweepstakes–mismatch process whereby reproduction is poorly coordinated with appropriate resources for larval development and recruitment can result in large variance in reproductive success among individuals and spawning aggregations. This process has been proposed to explain low ratio of genetic effective population size (Ne) to adult census size (N) ratios in marine species with high fecundity, pelagic spawning, and extensive mortality in early life stages. This process is also hypothesized to also account for very low Ne/N (≈ 0.001) observed in the federally endangered Rio Grande silvery minnow, Hybognathus amarus. This species is a freshwater fish that shares life-history features with marine pelagic spawners. We tested two key predictions of the sweepstakes–mismatch hypothesis using molecular data: (i) that temporally distinct samples of eggs differ in genetic composition and, (ii) that egg samples do not comprise a random subset of potential adult breeders. We present genetic data that supports both predictions and that are consistent with the hypothesis that high variance in reproductive success among adult breeders is an important factor that lowers Ne/N in H. amarus. This study highlights the importance of understanding the interaction of early life history and fragmentation in devising conservation plans for endangered aquatic organisms.

We assessed spatial and temporal patterns of genetic diversity to evaluate effects of river fragmentation on remnant populations of the federally endangered Rio Grande silvery minnow (Hybognathus amarus). Analysis of microsatellite and mitochondrial DNA detected little spatial genetic structure over the current geographic range, consistent with high gene flow despite fragmentation by dams. Maximum-likelihood analysis of temporal genetic data indicated, however, that present-day effective population size (NeV) of the largest extant population of this species was 78 and the ratio of effective size to adult numbers (NeV/N) was ∼ 0.001 during the study period (1999 to 2001). Coalescent-based analytical methods provided an estimate of historical (river fragmentation was completed in 1975) effective size (NeI ) that ranged between 105 and 106. We propose that disparity between contemporary and historical estimates of Neand low contemporary Ne/N result from recent changes in demography related to river fragmentation. Rio Grande silvery minnows produce pelagic eggs and larvae subject to downstream transport through diversion dams. This life-history feature results in heavy losses of yearly reproductive effort to emigration and mortality, and extremely large variance in reproductive success among individuals and spawning localities. Interaction of pelagic early life history and river fragmentation has altered demographic and genetic dynamics of remnant populations and reduced Neto critically low values over ecological time. Resumen: Estimamos los patrones espaciales y temporales de diversidad genetica para evaluar los efectos de la fragmentacion del rio sobre poblaciones remanentes del pez Hybognathus amarus federalmente en peligro. El analisis de ADN microsatelite y mitocondrial detecto escasa estructura genetica espacial en su rango de distribucion actual, lo que es consistente con un alto flujo genico a pesar de la fragmentacion por presas. Sin embargo, los analisis de probabilidad maxima de datos geneticos temporales indicaron que el tamano poblacional efectivo actual (NeV) de la poblacion mas grande era 78 y la relacion tamano efectivo – numero de adultos (NeV/N) fue ∼ 0.001 durante el periodo de estudio (1999 – 2001) Metodos analiticos coalescentes proporcionaron una estimacion del tamano efectivo historico (NeI ) (la fragmentacion del rio termino en 1975) que vario entre 105 y 106. Proponemos que la disparidad entre las estimaciones historicas y contemporaneas de Ney la baja Ne/N contemporanea resultan de cambios recientes en la demografia relacionados con la fragmentacion del rio. Hybognathus amarus produce huevos y larvas pelagicas que son transportadas rio abajo a traves de presas de desvio. Esta caracteristica de la historia de vida resulta en fuertes perdidas de esfuerzo reproductivo por emigracion y mortalidad, y en una varianza extremadamente amplia en el exito reproductivo entre individuos y sitios de desove. La interaccion de la historia de vida pelagica y la fragmentacion del rio ha alterado la dinamica demografica y genetica de las poblaciones remanentes y ha reducido a Nea valores criticamente bajos en tiempo ecologico.

Museum records indicate that Hybognathus placitus was introduced into the Pecos River, New Mexico during the early 1960s. Approximately 10 years later, a congener, Hybognathus amarus, was extirpated from the system. We used microsatellite and mtDNA data, ecological data and modelling, and a computer simulation approach to reconstruct the history of invasion and species replacement. To identify the potential role of hybridization and introgression, we genetically screened H. amarus (n = 389) from the Rio Grande, New Mexico, and H. placitus (n = 424) from the Pecos River, New Mexico using four nuclear microsatellites and a partial fragment of the mtDNA ND4 gene. Assignment tests excluded hybridization as a primary factor in species replacement and suggested a role for interspecific competition. Genetic analyses showed that H. placitus were introduced into the Pecos River from at least two genetically distinct source populations in the Canadian and Red rivers, Oklahoma. Lotka–Volterra models of interspecific competition indicated that the number of founding individuals could have been as few as 20 for H. placitus to have competitively displaced H. amarus in the Pecos River in 10 to 15 generations. Observed differences of allele frequencies between source and founder populations indicated that between 32 and 115 H. placitus individuals founded the Pecos River. Genetic and ecological data suggest that interspecific competition could have led to species replacement in this arid-land river system.

Similar morphology and confused historical taxonomy of Hybognathus hankinsoni (brassy minnow) and Hybognathus placitus (plains minnow) have made determination of their historic distributions and conservation status unclear in eastern Colorado basins. We developed logistic regression models from morphometric measurements to predict species identity of Hybognathus collections from Colorado and adjacent counties (n = 1154 specimens in 134 lots). A model based on orbit diameter, standard length, and eye position correctly predicted 98% of the specimens examined and 100% of the museum lots. Hybognathus hankinsoni have larger eyes centered on a horizontal line through the tip of the snout, whereas H. placitus have smaller eyes centered above the tip of the snout. The two species were historically sympatric in the Platte, Republican, and Smoky Hill River basins, whereas H. placitus was allopatric in the Arkansas River basin. The taxonomic characters defined here will allow accurate identification of fut...

Geomorphic changes resulting from the construction of dams, irrigation diversion structures, and flood control levees has separated the Rio Grande from its floodplain contributing to the decline of native fish species including the endangered Rio Grande silvery minnow (Hybognathus amarus). The species is currently restricted to 280-km of the river in New Mexico. Since 2006, the New Mexico Interstate Stream Commission has constructed 121 ha of floodplain habitat between the river levees to improve habitat. To determine if constructed habitats were being utilized by the Rio Grande silvery minnow and the fish community, a presence/absence study was conducted on eight constructed floodplains during 2008 and 2009, and one natural floodplain in 2008. A total of 14 481 fish were captured in fyke nets during both years: 3528 fish were captured from constructed floodplains and 8410 were captured from the natural floodplain in 2008: 2543 fish were captured from the constructed floodplains in 2009. Of this total, 11 602 of the fish were Rio Grande silvery minnow: 2180 Rio Grande silvery minnow were collected from constructed floodplains and 7356 from the natural floodplain in 2008; 2057 Rio Grande silvery minnow were collected from constructed floodplains in 2009. Gravid female and male expressing milt were collected both years. A total of 1173 unidentified larval fish and 363 Rio Grande silvery minnow eggs were also collected during the surveys. The results show that the Rio Grande silvery minnow and the fish community utilized the constructed and natural floodplains during the spring spawning season. Copyright © 2013 John Wiley & Sons, Ltd.

Ten years of river restoration at the Pueblo of Santa Ana have included projects focused on bioengineering, native plantings, and habitat creation for the federally listed endangered Rio Grande silvery minnow (Hybognathus amarus). When a natural river meander threatened to erode bankline adjacent to ageing cottonwoods and flank an instream grade control structure in the Rio Grande, the Pueblo and Bureau of Reclamation collaborated to create an ecologically based solution. A modified bendway weir project was implemented which included a series of 13 earthen-buried weirs. Earthen material was used to reestablish 2,000 linear feet of bankline from a 10 feet vertical height, 50 feet in length, to meet the water’s edge. During construction, a large scour pool associated with the vertical bank was filled. Additionally, the channel was moved toward the opposite bank and a spoil pile berm was removed that increased floodplain overbank inundation. Both scour pools and floodplain overbank inundation are important habitats during the silvery minnow’s life history leading the Pueblo to ask “how did reestablishing the bankline change the river channel at the project site and what were the short-term effects on river habitat and the fish community? Localized geomorphic and hydrologic changes were identified using channel cross-section surveys before (2008), immediately following (2009), and after construction (2010, 2011). The Pueblo used relative comparisons of the project site to reference sites for habitat change analyses based on ecological criteria described for the silvery minnow. Channel characteristics (thalweg location, habitat type, flow, depth, and sediment type) were evaluated for short-duration effects from project implementation. Fish community survey data was collected three times per year (March, July, November), before and after construction. Minnow catch per unit effort, fish species richness and diversity were analyzed using non-parametric statistics to identify differences. Lastly, the five most abundant fish species were compared for dominance before and after construction. The Pueblo’s analyses indicated that the project produced localized changes to the river channel resulting in a two year shift of the river’s thalweg. This resulted in some generally positive changes related to the silvery minnow’s preferred habitat and overall fish community. Despite these changes, the silvery minnow population was relatively unaffected leading the Pueblo to determine that the project successfully met the bankline reengineering objectives while minimizing disturbance to the species. 2637 World Environmental and Water Resources Congress 2012: Crossing Boundaries © ASCE 2012

The major histocompatibility complex (MHC) is a critical component of the adaptive immune response in vertebrates. Due to the role that MHC plays in immunity, absence of variation within these genes may cause species to be vulnerable to emerging diseases. The freshwater fish family Cyprinidae comprises the most diverse and species-rich group of freshwater fish in the world, but some are imperiled. Despite considerable species richness and the long evolutionary history of the family, there are very few reports of MHC sequences (apart from a few model species), and no sequences are reported from endemic North American cyprinids (subfamily Leuciscinae). Here we isolate and characterize the MH Class II beta genes from complementary DNA and genomic DNA of the non-model, endangered Rio Grande silvery minnow (Hybognathus amarus), a North American cyprinid. Phylogenetic reconstruction revealed two groups of divergent MH alleles that are paralogous to previously described loci found in deeply divergent cyprinid taxa including common carp, zebrafish, African large barb and bream. Both groups of alleles were under the influence of diversifying selection yet not all individuals had alleles belonging to both allelic groups. We concluded that the general organization and pattern of variation of MH class II genes in Rio Grande silvery minnow is similar to that identified in other cyprinid fishes studied to date, despite distant evolutionary relationships and evidence of a severe genetic bottleneck.

The influence of salinity on survival, specific gravity, and size of eggs of the endangered Hybognathus amarus (Rio Grande silvery minnow) was studied to provide insight into factors affecting their potential dispersal and fate. Under low salinity conditions egg specific gravity declined significantly in the first hour after spawning as the perivitelline space of the egg filled with water. Egg specific gravity achieved a minimum value approximately 1 h post-spawning and remained approximately constant until hatching, which occurred near 48 h post-spawning at 20°C. Specific gravity of the egg depended on the salinity of the water surrounding the egg: hardened eggs changed rapidly in diameter and specific gravity when exposed to water of higher salinity. Size and specific gravity of H. amarus eggs also differed when the eggs were incubated in different groundwater sources. Experiments indicated that calcium chloride saline solution had a greater effect on egg specific gravity and size than did solutions of sodium or potassium chlorides. Survival of H. amarus eggs declined sharply at salinity greater than 3 (practical salinity units, PSU) and was only 5% at a salinity of 8. Habitat restoration to benefit H. amarus should consider the salinity of habitats in which eggs incubate. El efecto de la salinidad sobre la supervivencia, gravedad específica y talla de los huevos del ciprínido puesto en peligro de extinción, Hybognathus amarus, fue estudiado para proporcionar información sobre los factores que afectan la dispersión y el destino de los huevos. Bajo condiciones de salinidad baja la gravedad específica del huevo disminuyó de forma significativa durante la primera hora después de la puesta, a medida que el espacio del perivitelino del huevo se fue llenando de agua. la gravedad específica del huevo alcanzó un valor mínimo 1 hora después de la puesta y quedó aproximadamente constante hasta eclosión, que ocurrió alrededor de 48 horas tras la puesta a 20˚C. la gravedad específica del huevo dependió de la salinidad del agua que le rodeaba. los huevos con corion endurecido cambiaron rápidamente en diámetro y gravedad específica cuando fueron expuestos a agua de salinidad más alta. El tamaño y la gravedad específica de los huevos de H. amarus también se diferenciaron cuando los huevos fueron incubados en diferentes fuentes de agua subterránea. Los experimentos indicaron que la solución salina del cloruro de calcio tuvo un mayor efecto sobre la gravedad específica del huevo que las soluciones de los cloruros del sodio o del potasio. Expuestos a soluciones de salinidad de más de 3 (PsU), la supervivencia de los huevos de H. amarus disminuyó claramente, bajando a sólo el 5% en la solución de 8. la restauración del hábitat con el objetivo de beneficiar a H. amarus debe considerar la salinidad de los hábitats en los cuales el huevo incuba.

A spatially intensive survey in 1989 of 52 sites in the Red River drainage in southwest Oklahoma and surveys in all years from 1978 to 1987 on four sites in the drainage provided evidence that construction of Altus Dam on the North Fork of the Red River caused major changes in fish community structure in the river above the dam. Pre-impoundment data on the fish communities were scanty, but the inferences they allowed were similar to those obtained by comparing fish assemblages in the North Fork above the dam with assemblages elsewhere in the drainage, particularly along Salt Fork, which had similar habitat characteristics. Twenty-five species were collected in the North Fork above Altus Dam, compared to 33 in the Salt Fork and 34 in the North Fork below the dam. The speckled chub Macrhybopsis (formerly Hybopsis) aestivalis and the chub shiner Notropis potteri were absent in the North Fork above Altus Dam but fairly common in similar streams elsewhere in the area. The plains minnow Hybognathus pla...