Spatial and Temporal Distribution of the Asian Fish Tapeworm Bothriocephalus acheilognathi (Cestoda: Bothriocephalidea) in the Rio Grande (Río Bravo del Norte)

We quantified the availability and utilization of habitat types by eight small‐bodied cyprinid fish species, including the federally threatened Pecos bluntnose shiner Notropis simus pecosensis, in the Pecos River, New Mexico. The Pecos River is a medium‐sized, sand‐bed river with a highly variable hydrograph and some reaches characterized by historic and recent periods of flow intermittency. Fish habitat was described in four reaches at flows of 0.05–2.29 m3/s by means of a simultaneous, coordinated program of channel topographic surveys, mesohabitat mapping, fish sampling, and measurement of microhabitat and chemical parameters. We determined that fish habitat in this sand‐bed river was effectively described at the mesohabitat scale. Furthermore, mesohabitats were visually distinguishable and separable by means of hydraulic and geomorphic parameters and the relationship between flow and depth, velocity, and velocity : depth ratios. The eight cyprinid species in the Pecos River primarily used four mesohabitat types that were consistently available at the full range of flows examined, including perpendicular and parallel plunges, backwaters, and slackwaters. In winter, five species (red shiner Cyprinella lutrensis, plains killifish Fundulus zebrinus, plains minnow Hybognathus placitus, Arkansas River shiner N. girardi, and sand shiner N. stramineus) shifted to backwaters, where water temperatures were relatively warmer than those of the main channel. Runs, flats, and riffles were generally the most available mesohabitat types, but their availability changed with flow; only four species (red shiner, plains killifish, speckled chub Macrhybopsis aestivalis, and sand shiner) selected these types, and they did so infrequently in summer. The Pecos bluntnose shiner was a habitat specialist that selected primarily rare plunge pools at sandbar faces, whereas species such as the red shiner were habitat generalists that used a variety of mesohabitat types. We found that a range of base flows sustained the preferred habitats of the eight cyprinid species and that no single flow maximized this preferred habitat because of a scaling effect of flow on sand bedforms.

The Asian fish tapeworm (Schyzocotyle acheilognathi) is an important fish parasite with a wide host range that infects over 300 species of fish worldwide.Schyzocotyle acheilognathihas been reported from eastern coastal areas of Australia, but has not been previously reported in Western Australia (WA). During a control program for invasive freshwater fishes in south-western WA, a region with a unique and highly endangered freshwater fish fauna, tapeworms identified asS.acheilognathifrom their distinctive scolex morphology were found at a prevalence of 3.3% in goldfish (Carassius auratus), 37.0% in koi carp (Cyprinus carpio haematopterus) and 65.0% in eastern gambusia (Gambusia holbrooki) in a small suburban lake to the north of Perth. For molecular confirmation, the 18S ribosomal RNA gene was targeted at hypervariable V4 region. Koi carp isolates were 100% identical toS.acheilognathiisolated from varying hosts, including the red shiner (Cyprinella lutrensis) and a human sample. Sequences obtained from two eastern gambusia were identified asS.acheilognathi, but formed a discrete cluster and may represent a novel genotype. Isolates from two other eastern gambusia and two goldfish formed a distinct clade with only 91.9% similarity to previously sequenced isolates ofS.acheilognathi. This emphasizes the importance of molecular identification methods in addition to morphological identification. The presence and potential for transmission of these parasites in south-western WA may threaten the health of native fishes, which are immunologically naïve to this introduced parasite. Immediate control or containment measures should be implemented to halt the spread of these parasites.

Passive integrated transponder (PIT) tags are commonly used to uniquely identify tagged individuals. Much of what we currently know about the feasibility of using PIT tags in fish ecology research has been studied in salmonids. The recent development of smaller tags has prompted research into their effects on small-bodied fishes. In a laboratory setting, I assessed the effects of PIT tags on Red Shiner Cyprinella lutrensis and Sand Shiner Notropis stramineus over 48 days. Survival was high (>97%) for both species. Tag retention was relatively high (82%) for Red Shiner, but low (51%) for Sand Shiner. Logistic regression models testing the effects of length of tagged fishes on survival and tag retention were non-significant. Growth was not affected by the presence of a PIT tag. This study suggests that Red Shiner and Sand Shiner > 45 mm can be successfully tagged with 9 mm PIT tags.

The gut microbiome is a highly intricate ecosystem that exerts a pivotal influence on the host’s physiology. Characterizing fish microbiomes is critical to understanding fish physiology and health, but little is known about the ecology and colonization dynamics of microorganisms inhabiting fish species. In this study, we investigated the bacterial communities of two small-bodied fish species, Cyprinella lutrensis (red shiner) and Notropis stramineus (sand shiner), two fish species where gut microbiomes have not been investigated previously and surrounding waters, collected from rivers in Nebraska, USA. Our study focused on evaluating microbial diversity in small-bodied fish and identifying autochthonous microbes present within these species irrespective of location to better understand bacterial community composition and possible roles of such bacterial species. Our results revealed that both red shiner and sand shiner exhibited gut bacterial communities dominated by typical bacterial phyla found in freshwater fish. The phylum Bacteroidota was minimally abundant in both species and significantly lower in relative abundance compared to the surrounding water microbial community. Furthermore, we found that the gut microbiomes of red shiner and sand shiner differed from the microbial community in the surrounding water, suggesting that these fish species contain host-associated bacterial species that may provide benefits to the host such as nutrient digestion and colonization resistance of environmental pathogens. The fish gut bacterial communities were sensitive to environmental conditions such as turbidity, dissolved oxygen, temperature, and total nitrogen. Our findings also show bacterial community differences between fish species; although they shared notable similarities in bacterial taxa at phyla level composition, ASV level analysis of bacterial taxa displayed compositional differences. These findings contribute to a better understanding of the gut bacterial composition of wild, freshwater, small-bodied fish and highlight the influence of intrinsic (host) and environmental factors on shaping the bacterial composition.

The Blue Sucker Cycleptus elongatus is an imperiled North American catostomid in need of management and protection. No hard structures are validated for aging this species, but past studies focused on somatic structures such as fin rays and scales. Calculated parameters (mortality, recruitment, growth) that inform management decisions are directly influenced by the accuracy and precision of the hard structure used to estimate age. We identify the most precise and credible structure with which to age Blue Suckers while also completing the first in‐depth investigation of their otoliths. We collected Blue Suckers (n = 168) from the lower Wabash River and compared ages estimated from scales, opercles, pectoral fin rays, and lapillus otoliths but were unsuccessful in estimating ages from cleithra. We identified structure bias between all structures and found scales (n = 67; maximum = 11 years, mean = 8.2 years) and opercles (n = 65; maximum = 15 years, mean = 8.3 years) to be substantially less precise than pectoral fin rays and lapillus otoliths. We found that otoliths (n = 128; maximum = 42 years, mean = 13.5 years) were more precise than fin rays (n = 167; maximum = 20 years, mean = 9.6 years) and yielded a much higher range of ages. We could not identify any range of ages or total lengths in which (nonlethal) fin ray age could be accurately corrected to (lethal) otolith age. Thin‐sectioned otoliths are the gold standard for aging most fishes, including numerous age‐validated catostomids, and the credibility of Blue Sucker otolith age estimates was additionally supported by a strong correlation between whole lapillus mass and estimated age (R2 = 0.89). Overall, evidence indicates that Blue Sucker lapillus otoliths yield more precise and credible age estimates than other hard structures.

Fishes were collected in four mainstem reaches and eight tributary reaches in the Keya Paha River basin during May and June 2002. Most reaches were characteristically run habitats with sand substrates and riparian pastures. Data were combined with historical records to construct a basin-wide ichthyofaunal list which comprised 38 species from seven families. Dominant species were sand shiners (Notropis ludibundus; 47%), red shiners (Cyprinella lutrensis; 37%), and brassy minnows (Hybognathus hankinsoni; 8%). Dominant game species were bluegill (Lepomis machrochirus) and channel catfish (Ictalurus punctatus). We found one species previously listed as rare in South Dakota -plains topminnow (Fundulus sciadicus), and four species not previously found in the Keya Paha River—silver chub (Macrhybopsis storeriana), river carpsucker (Carpiodes carpio), northern pike (Esox lucius), yellow perch (Perca flavescens).

Power transfer theory (PTT), a useful paradigm in electrofishing, asserts that the threshold power density (Dt, μW/cm3) transferred from water to fish for immobilization is dependent on the conductivity (μS/cm) of the water (σw) and of the fish (σf). Larger differences between the two conductivities require higher applied power densities and may make capture more difficult. Over a range of water conductivities, Dt as a function of σw will form a U-shaped curve, and the minimum provides an estimate of σf and Dm (the lowest value of Dt that occurs when σw and σf are equal). Studies have demonstrated a narrow range of σf (56–160 μS/cm) relative to the conductivity of natural waters (10–5,000 μS/cm). However, these σf values are for larger species. Electrofishing may also be directed at the capture of smaller species or diverse communities. In an experimental tank, we estimated Dm and σf for a small cyprinid, the Red Shiner Cyprinella lutrensis (TL = 35–64 mm) and a smaller poeciliid, the Western Mosquitofish Gambusia affinis (TL = 23–46 mm). We estimated Dm and σf to be 120 μW/cm3 and 23 μS/cm, respectively, for Red Shiners (n = 72) and 143 μW/cm3 and 23 μS/cm, respectively, for Western Mosquitofish (n = 23). These values for σf are less than half the minimum of previously reported values, and our Dm estimates are less than those that have been reported for game species of similar length (200–300 μW/cm3). Our results serve to explain why smaller species require higher applied power densities and are more difficult to capture from an assemblage of various species and sizes.

We examined survival, competition, and recruitment among cyprinids that were subjected to interspecific and intraspecific competition and chronic heat stress in large, outdoor experimental streams. The study was conducted in 2011 during the hottest summer (also one of the driest summers) recorded in Texas. We measured survival of Red Shiners Cyprinella lutrensis, Blacktail Shiners Cyprinella venusta, and Central Stonerollers Campostoma anomalum stocked at varying densities to examine competitive interactions. Trophic interactions among Blacktail Shiner density treatments were assessed with stable isotope analysis (SIA), and mitochondrial markers were used to examine the lineage of young‐of‐the‐year shiners spawned during the study. Stocking survival was significantly greater for Red Shiners, and both shiner species demonstrated higher overall survival rates than Central Stonerollers. Although SIA results were variable among replicate streams, more generalist foraging patterns were observed for Blacktail Shiners in the high‐density treatment (intraspecific competition; no Red Shiners present) relative to the low‐density Blacktail Shiner treatment. Less trophic redundancy was observed in the interspecific competition treatment (Blacktail Shiners and Red Shiners co‐occurring) compared with the same density of Blacktail Shiners only (high‐density treatment). Despite the potentially lethal water temperatures, including 4 d on which water temperatures exceeded 37°C, mitochondrial sequences showed that both Red Shiners and Blacktail Shiners were able to spawn during the study. These results collectively highlight potential mechanisms for explaining fish assemblage responses at local and landscape scales, such as the Red Shiner's recent range expansion and increased abundance in some areas of Texas. Our findings are relevant for forecasting regional changes in fish species distributions in response to more frequent droughts and warmer summers due to climate change.Received March 1, 2013; accepted March 11, 2014

Human disturbance increases the invasibility of lotic ecosystems and the likelihood of hybridization between invasive and native species. We investigated whether disturbance contributed to the invasion of red shiner (Cyprinella lutrensis) and their hybridization with native blacktail shiner (C. venusta stigmatura) in the Upper Coosa River System (UCRS). Historical records indicated that red shiners and hybrids rapidly dispersed in the UCRS via large, mainstem rivers since the mid to late 1990s. We measured the occurrence and abundance of parental species and hybrids near tributary-mainstem confluences and characterized populations at these incipient contact zones by examining variation across morphological traits and molecular markers. Red shiners represented only 1.2% of total catch in tributaries yet introgression was widespread with hybrids accounting for 34% of total catch. Occurrence of red shiners and hybrids was highly correlated with occurrence of blacktail shiners, indicating that streams with native populations are preferentially colonized early in the invasion and that hybridization is a key process in the establishment of red shiners and their genome in new habitats. Tributary invasion was driven by post-F1 hybrids with proportionately greater genomic contributions from blacktail shiner. Occurrence of red shiners and hybrids and the relative abundance of hybrids significantly increased with measures of human disturbance including turbidity, catchment agricultural land use, and low dissolved oxygen concentration. Red shiners are a significant threat to Southeast Cyprinella diversity, given that 41% of these species hybridize with red shiner, that five southeastern drainages are invaded, and that these drainages are increasingly disturbed by urbanization.

The upstream effects of reservoirs on stream fish assemblages were highly localized in 3rd- through 5th-order streams in the Great Plains, USA. Streams that differed in connectivity to reservoirs were sampled at their confluences with a river or reservoir and between the confluence and the stream's origin. Sites at confluences had higher total, nonnative, and reservoir species richness than middle sites. Variability in fish assemblage structure upstream of reservoirs was influenced by catchment area, stream size, gradient, and reservoir connectivity. Confluence sites connected to reservoirs were correctly classified based on the presence of red shiners (Cyprinella lutrensis) and bluntnose minnows (Pimephales notatus) and the absence of sand shiners (Notropis stramineus); middle sites on connected streams were classified by the absence of redfin shiners (Lythrurus umbratilis). Intensive sampling across pool habitats within two streams isolated by a reservoir indicated that abundance of common reservoir species was related to pool size, turbidity, and canopy cover, but not proximity to the reservoir. These data suggest that streams connected to reservoirs can maintain diverse native fish communities with minimal invasions by reservoir-dwelling species, but a fraction of the community either has been lost or occurs at low abundance (e.g., sand shiners and redfin shiners).

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...

Relations between annual abundance of three introduced fishes and body condition of an endangered piscivore, Colorado pikeminnow Ptychocheilus lucius, in the upper Colorado River were assessed to aid prioritization of non-native fish control efforts. Relative condition (Kn: mass at a given length) was monitored during spring, 1991–2013. Positive and significant relations were found between annual mean Kn and backwater densities of two common non-native, small-bodied, cyprinid species in downstream reaches of the 293 km study area. High mean Kn in spring followed years when fall densities of fathead minnow Pimephales promelas and red shiner Cyprinella lutrensis were high. No such relation was found with a third species, sand shiner Notropis stramineus. These three species have dominated zero-velocity habitats since their introduction in the 1960s. No relation was found between mean Kn prior to spawning and subsequent abundance of Colorado pikeminnow young-of-the-year (YOY) 3 months post spawning, suggesting mean Kn was not a driver of fall YOY abundance. Based on predatory interactions with larval native fishes documented in the literature, red shiners were deemed detrimental to Colorado pikeminnow despite their food value. Sand shiners appeared benign: non-predatory and less important as food. Fathead minnows, however, might be beneficial. They appear non-predatory on fish larvae while providing an important food source for various Colorado pikeminnow life stages. Managers need to weigh these benefits when considering control efforts.

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.

Over 50% of imperiled fish species in Texas are endemic to the Rio Grande drainage. Bothriocephalus acheilognathi was recently collected from the Rio Grande and might pose further risk for these species. We examined the impact of this exotic tapeworm on fish condition and reproduction using a surrogate species, Cyprinella lutrensis. Fish were collected from two mainstem sites and one tributary site within Big Bend National Park from February through December 2006. Adjusted mean Fulton condition was higher for uninfected fish than infected fish. No differences were detected between uninfected fish for gonadosomatic indices, number of vitellogenic oocytes, number of late vitellogenic oocytes, late vitellogenic occyte maximum diameters, or proportion of late vitellogenic oocytes to total number of oocytes. These findings suggest that C. lutrensis is investing energy in reproduction at the expense of somatic growth, but energy invested in reproduction was not affected by tapeworm occurrence.

Seasonal movements cued by environmental variables are a critical component of riverine fish life history. Life‐history events for species such as blue sucker Cycleptus elongatus are likely cued by discharge and temperature and may be disrupted if those life‐history events and environmental regimes are mismatched. However, this effect may be dependent upon the habitat occupied when environmental cues are received by individuals. We tracked telemetered blue sucker in the Colorado River, Texas, USA, from 2015 to 2017 and modelled the relative effects of discharge, temperature and habitat structure on seasonal movement patterns. Tagged fish varied in their propensity to move, although most returned to their original tagging locations. Decreasing temperatures and increasing discharge resulted in increased seasonal movements. Temperature and discharge had the largest effect on movement behaviour, but the magnitude of movements was largely dependent on the year. Temperatures between 12 and 19°C and discharges between 10 and 240 m3s−1 resulted in greater probabilities of spawning movements. Spawning was most probable in 2015 and reduced or halted in 2016 and 2017. Future climate scenarios suggest North America will experience increased drought, warmer temperatures and more variable weather patterns. These future scenarios could negatively impact blue sucker by disrupting environmental cues and habitat availability for seasonal life‐history events. Our results suggest temperature and discharge are critical cues for the species, but that their combined effect is largely dependent on the occupied habitat.