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Round Goby (Neogobius melanostomus) has invaded high diversity tributaries of the Laurentian Great Lakes, including those supporting multiple species of conservation concern. The extent and magnitude of ecological impacts on benthic riverine fishes is poorly understood, especially changes in diet overlap and feeding strategy. We used a before-after study design to examine the impact of Round Goby on native benthic riverine fishes, including the Threatened Eastern Sand Darter (Ammocrypta pellucida) in the Sydenham River, Ontario, Canada. To evaluate shifts in diet overlap and feeding strategy, fishes were collected with multiple gears and the direct (diet overlap with Round Goby) and indirect (diet overlap among native benthic fishes) impacts of Round Goby were assessed. Prior to the arrival of Round Goby, six ecologically significant diet overlaps occurred among the studied native benthic fishes; whereas, following arrival, 20 ecologically significant diet overlaps occurred, with 6 out of 8 species, including Eastern Sand Darter, showing significant, direct diet overlap with Round Goby. Fishes exhibiting significant diet overlap with Round Goby shifted feeding strategies to become more specialized, a change in feeding consistent with potential competitive effects. Although the long-term consequences of invasion-induced diet and feeding shifts remain poorly understood, increased competitive interactions suggested by diet overlap may be occurring between Round Goby and native benthic riverine fishes and may exacerbate the observed decline of native species.

The Strawberry Darter Etheostoma fragi is endemic to the Strawberry River drainage in northcentral Arkansas, where its distribution and status have not been assessed since the mid-1990s. A status survey was conducted during the summers of 2015 and 2016. Sixty-four sites were sampled (32 each summer) within the Strawberry River drainage. Sites were surveyed 4 times each using a kick-seine. A total of 236 E. fragi were observed during the study. E. fragi were observed at 24 of 64 sites, including 15 tributary and 9 main stem sites. Strawberry Darters were observed at sites with a median (range) dissolved oxygen of 9.2 (5.7–11.9) mg/L, median stream flow of 0.2 (0.1–0.7) m/s, median pH of 8.1 (6.7–9.4), median water temperature of 22.0 (13.9–29.3) °C, and median depth of 0.2 (0.1–0.7) m. Presence/absence data were analyzed with occupancy modeling, which estimates informed occupancy rate (hereafter, occupancy) and probability of detection. The drainage-wide occupancy (± SE) was 0.41 ± 0.06 and the probability of detection was 0.56 ± 0.06. A reach covariate model fit our data the best (209.81 AICc). This model estimated an occupancy of 0.54 ± 0.09 and a probability of detection of 0.64 ± 0.06 in the upper reach, an occupancy of 0.20 ± 0.11 and a probability of detection of 0.51 ± 0.17 in the middle reach, and an occupancy of 0.39 ± 0.31 and a probability of detection of 0.19 ± 0.16 in the lower reach The drainage-wide occupancy was lower (0.32 difference) than an occupancy based on historical data (0.73 ± 0.11). These results suggest a decline in the status of E. fragi and justify conservation measures to preserve this species.

The southeastern United States harbors one of the most diverse temperate freshwater fish faunas of the world. Unfortunately, due to improper land use practices and habitat degradation, many of the species in this region are imperiled and may become extinct without appropriate conservation efforts. This study examined the population dynamics of an endangered endemic darter of southwest Kentucky, the Relict Darter (Etheostoma chienense) and its sister taxon, the undescribed Clarks Darter (Etheostoma cf. oophylax). Mitochondrial sequence data coupled with SNP data were used to infer population structure, gene flow, genetic variation, and effective population sizes of both species. The results from this study, based on 160 individuals from nine localities, indicate that the endangered Relict Darter possesses limited genetic variation based on mitochondrial DNA haplotypes (N = 4). In addition, SNP data (6.8 k markers) further indicates limited genetic structure (K = 1), as well as a low effective population size (143–918), suggesting that the Relict Darter can be managed as a single, panmictic conservation unit. It is suggested that conservation efforts be taken to protect remaining habitats, augment the system with artificial spawning substrates, and, as a last resort (if needed), supplement the natural population with captive reared individuals. Ethesotoma cf. oophylax showed some genetic variation among distant sites, but more samples are needed throughout the range in order to fully understand the population dynamics of this species.

Candy Darters (Etheostoma osburni) and Variegate Darters (E. variatum) are both native to West Virginia and Virginia. The geographic ranges of these two species were historically separated by Kanawha Falls, a natural barrier to fish dispersal located at Glen Ferris, WV. In the early 1980s, Variegate Darters or putative hybrids (E. osburni × E. variatum) were first collected at locations upstream of Kanawha Falls, and have since undergone range expansion. Hybridization with the Variegate Darter was one of the threats that led to the Candy Darter being listed as Endangered under the U.S. Endangered Species Act in 2018. Genetic and morphologic data were examined for individuals from the New, Gauley, and Greenbrier river drainages. Individuals were genotyped using a suite of 5 diagnostic microsatellite loci to investigate potential hybridization. Widespread hybridization was found throughout populations of Candy Darters, with the geographic range of hybridization expanding from 2004 to 2014. A hybrid zone was observed, with the highest levels of Variegate Darter introgression representing the kernel within this zone and the locations of first-generation (F1) hybrids at the periphery. F1 hybrids were morphologically intermediate within and across characters for parental species. Introgressive hybridization threatens the genetic integrity of the Candy Darter, and may lead to population extirpation or extinction.

While population genetic structuring is easily identified, the causes of the structure can be difficult to determine. Habitat fragmentation in aquatic systems has often been identified as a major source of increased population structure and decreased genetic diversity in fish, including benthic resident species such as darters. However, these findings are often not replicated across natural and manmade barriers and come from endangered or threatened populations where the genetic structure is likely already compromised due to small population size. To evaluate the factors involved in structuring a healthy darter population, we genotyped 506 tessellated darters from 18 sites in three different river drainages and one large lake. Sites were all in the same watershed but separated from one another by one or more of three different types of barriers: dams, natural fall lines and causeways. We found that while diversity and allele frequency varied largely by drainage, within drainage variation was minimal even across multiple barriers. No single barrier type appeared to be more formidable than any other. Our results indicate that healthy populations of darters may naturally be structured by drainage, but likely disperse across barriers enough to retain drainage-wide homogeneity.

Play with objects by birds is recorded usually for nestlings and juveniles. This behaviour is regarded as important for motor development and practice of essential skills, mostly foraging and breeding. Play is recorded for the Anhinga (Anhinga anhinga) in North America. For the remaining three recognised species play with objects seems unreported. Herein I present events of play with objects by a maturing individual of the Australasian Darter (Anhinga novaehollandiae) recorded at the urban area of Sydney, southeastern Australia. In one of the play events, the darter played with a stick it broke from a partly submerged tree it was resting on. In another event, the bird picked a floating pod, tossed it into the air and caught it again. As the Australasian Darter maturing individual possibly was a male, it could be practicing to gather sticks for nest construction, whereas playing with the pod is related to prey handling.

The process of speciation is often synonymous with the evolution of reproductive isolation, and the tempo at which reproductive barriers evolve can provide insight into the underlying mechanisms of divergence. Darters are a diverse group of North American freshwater fish in which behavioral isolation appears to evolve rapidly; however, little is known about hybrid sterility among darter species. Here, six allopatric pairs of darter species were hybridized via in vitro fertilization and offspring were reared to reproductive age. Hybrid sterility appears more pronounced in male hybrids. Additionally, levels of hybrid sterility increase with genetic distance across species pairs. Understanding sex determination and sex-specific gene expression in darters will provide further insight into the evolution of hybrid sterility.

Headwater fishes in the southeastern United States make up much of the fish biodiversity of the region yet many are imperiled. Despite this, the specific habitat requirements of imperiled headwater fishes in lowland Coastal Plain streams have rarely been quantified. Using data collected over three years of seasonal sampling we provide estimates of the microhabitat requirements of the imperiled Yazoo darter (Etheostoma raneyi Suttkus and Bart), a small benthic insectivore. Our results indicate that the species is a microhabitat specialist and that optimum microhabitat within degraded contemporary streams consists of a narrow range of water depths (about 20–30 cm), current velocity ≥ 0.25 m·s−1, complex stable debris piles, rooted macrophytes, and likely coarse substrate. No pronounced or generalized seasonal shifts in microhabitat use occurs, and no evidence exists for intraspecific partitioning of microhabitat. Though stable and complex instream cover is one of the most important variables explaining variation in microhabitat use by Yazoo darters, such cover is rare in the degraded streams within the range of the species. Current conservation classifications of the Yazoo darter by governmental agencies and nongovernmental organizations as well as associated management plans that are based on the assumption that Yazoo darters are habitat generalists should be reviewed in recognition of the increased risk of decline because Yazoo darters are microhabitat specialists. These considerations should also be extended to other closely related imperiled species of snubnose darters.

The importance of competition among stream salamanders and other stream vertebrates in headwater systems is understudied. We conducted a replicated artificial stream experiment to evaluate competitive interactions among three common vertebrates. In this experiment, we measured change in body condition of salamanders in the black-bellied dusky complex (Desmognathus quadramaculatus/folkertsi) in the presence of two different fish species, Common Creek Chub (Semotilus atromaculatus) and Coosa Darter (Etheostoma coosae). There was no statistically significant change in body condition between the control and darter present treatments. However, salamander body condition was significantly reduced in the presence of the creek chubs suggesting an asymmetric competitive interaction between those two species. While predation is often cited as a potential mechanism limiting the distribution of stream species, the role of interspecific competition may be just as vital. Overall, our results highlight that competition, and not solely predation, may explain why some stream salamanders are restricted to headwater reaches.

The threatened Okaloosa darter (Etheostoma okaloosae) is found almost exclusively in the Choctawhatchee Bay of Florida, and its habitat is threatened by natural disasters and water pollution. In this study, the complete mitochondrial genome of E. okaloosae has been determined by polymerase chain reaction method for the first time. The overall base composition of E. okaloosae mitogenome is 26.1% for A, 28.2% for C, 18.2% for G and 27.5% for T. The percentage of G+C content is 45.7%. The mitogenome is a circular DNA molecule of 16,616 bp in length with a D-loop region and contains 22 transfer RNA (tRNA) genes, two ribosomal RNA (rRNA) genes and 13 protein-coding genes (PGCs). Phylogenetic analysis suggests that E. okaloosae is closely related to Etheostoma nigrum and Etheostoma radiosum. The mitochondrial genome sequencing of E. okaloosae in this study provides important molecular data for conservation genetic studies.

Sexual dimorphism is hypothesized to be the result of differential selection pressures between the sexes. Dimorphic traits can serve as indicators of mate quality, altering mate preferences in the opposite sex in favor of a conspicuous trait. Common indicators of mate quality include color and size, with traditional assumptions and evidence predicting a preference for more colorful and/or larger sized mates in many species. Both male and female preferences for more colorful and larger mates within a species are rarely examined simultaneously, however. We examined a sexually dichromatic freshwater fish, Percina roanoka and found that male coloration is positively correlated with size, suggesting color may function as an indicator of viability. We tested preferences for coloration and size in both sexes in a dichotomous mate choice setup in which only visual signals were exchanged. Neither females nor males exhibited a color or size preference in individuals of the opposite sex. Visual cues alone therefore appear to be insufficient to elicit a significant preference in both sexes of this species. Male coloration in P. roanoka does not appear to be driven solely by female preference.

Speciation research focuses on the evolutionary mechanisms responsible for the origin of species, and recent treatments have distinguished ecological and mutation-order speciation as distinct evolutionary processes. Using a research framework that considers ‘speciation phenotypes’ (sensu Shaw and Mullen in Genet 139(5):649–661, 2011) and a modified hierarchy of speciation models, we address whether speciation in benthic fishes commonly called darters proceeds under divergent ecological selection or a mutation-order process. We examined neutral genetic divergence, sexual signal (male color) divergence, environmental differences, and geographic distance in 66 species pair comparisons. Modified Mantel tests detected significant relationships between genetic distance and overall male color differences, as well as geographic distance and overall male color differences; however, after accounting for the correlation of male color and geographic distance with genetic distance using a partial Mantel test, no relationship was observed between male color and geographic distance. Neither microhabitat nor climatic measures of environmental differences correlated with overall male color differences. Color difference scores for discrete color categories (i.e., red/orange/yellow, black, and blue/green) differed in their correlations with explanatory variables, implying different selection regimes may be influencing each component of darter color patterns. Our results do not support a primary role for divergent ecological selection shaping early divergence of darter sexual signals. Instead, a model of mutation-order speciation may best explain the clock-like manner of changes in male color among darter species.

While extensive empirical and theoretical work has focused on the evolution of costly cooperation (particularly in group-living species), less attention has been paid to more low-risk or immediately beneficial forms of cooperation. In some non-group-living darters, alloparental care (or allocare) by subordinates has been noted to result from by-product benefits as small territorial (subordinate) males adopt and provide care to the abandoned eggs of large territorial (dominant) males. In the tessellated darter (Etheostoma olmstedi), allocare also results from sneak fertilization. However, information on the rate of allocare by tessellated darters is contradictory: prior behavioral work suggested that it is very common, while a genetic examination showed males to primarily care for their own young. We found behavioral and genetic evidence of very high levels of allocare at our study location. The relative size of the assigned fathers of young to the alloparental male is consistent with the idea that initial allocare primarily results from sneak fertilization (“cuckoldry-based allocare”), but later allocare results from subordinate males caring at previously abandoned nests (“adoption-based allocare”). Larger males appeared to breed more frequently at different nests, but did not father more individual offspring than smaller males. Finally, low relatedness between abandoning and alloparenting males suggests that kin selection does not contribute to alloparental care. We discuss how variation in nest availability may explain the inconsistent findings of the rate of alloparental care in the tessellated darter, and how increased research in this and similar systems can expand our understanding of the evolution of cooperation.

Imperiled Okaloosa darters (Etheostoma okaloosae) are small, benthic fish limited to six streams that flow into three bayous of Choctawhatchee Bay in northwest Florida, USA. We analyzed the complete mitochondrial cytochrome b gene and 10 nuclear microsatellite loci for 255 and 273 Okaloosa darters, respectively. Bayesian clustering analyses and AMOVA reflect congruent population genetic structure in both mitochondrial and microsatellite DNA. This structure reveals historical isolation of Okaloosa darter streams nested within bayous. Most of the six streams appear to have exchanged migrants though they remain genetically distinct. The U.S. Fish and Wildlife Service recently reclassified Okaloosa darters from endangered to threatened status. Our genetic data support the reclassification of Okaloosa darter Evolutionary Significant Units (ESUs) in the larger Tom’s, Turkey, and Rocky creeks from endangered to threatened status. However, the three smaller drainages (Mill, Swift, and Turkey Bolton creeks) remain at risk due to their small population sizes and anthropogenic pressures on remaining habitat. Natural resource managers now have the evolutionary information to guide recovery actions within and among drainages throughout the range of the Okaloosa darter.

In the present study, five species of Contracaecum Railliet & Henry 1912 (Nematoda: Ascaridida), including Contracaecum bancrofti, Contracaecum microcephalum, Contracaecum variegatum, Contracaecum eudyptulae, and Contracaecum ogmorhini, were redescribed using light and scanning electron microscopy. In addition, in order to elucidate their taxonomic status, first and second internal transcribed spacers (ITS-1 and ITS-2, respectively) of nuclear ribosomal DNA of each morphospecies were characterized. Analyses of sequence and morphological data sets suggested that C. bancrofti, infecting the Australian pelican Pelecanus conspicillatus, is a valid species and is distinct from C. micropapillatum reported from pelicans in the northern hemisphere. C. microcephalum from cormorants Phalacrocorax melanoleucos and C. variegatum from the darter Anhinga melanogaster and from P. conspicillatus as well as C. eudyptulae from the little penguin Eudyptula minor were also considered as distinct species, which can be differentiated from one another morphologically based on the lengths of spicules and genetically based on the sequences of ITS-1 and ITS-2. Comparison of sequence data of ITS-1 and ITS-2 for the members of C. ogmorhini sensu lato from pinnipeds with those of previous studies suggested that only ITS-2 can be used for differentiation between C. ogmorhini sensu stricto and Contracaecum margolisi, occurring in the southern and northern hemispheres, respectively. Analyses of the ITS-1 and ITS-2 sequence data of Contracaecum spp. in the present study supported the distinction among species of Contracaecum based on morphological data and were useful in confirming the taxonomic status of individual species in Australia.

Extensive research has focused on understanding the evolution of parental care, with fishes providing important model systems for understanding patterns of variation within and between species. Classic theory predicts that individuals will care for offspring when the fitness benefits through increased offspring survival and growth outweigh the cost to the parents through decreased future reproductive opportunities. Yet, a puzzling observation not explained by this basic theory is the fact that in some species individuals defend and provision unrelated offspring and thus exhibit alloparental care. The tessellated darter, Etheostoma olmstedi, represents one of the first known examples of allopaternal care in fishes. In this species, males often clean and guard eggs fertilized but deserted by other males. Allopaternal care has been argued to occur in the tessellated darter because of competition for a limited number of mating sites where less dominant males accept territories with eggs when other breeding sites are not available. Here, we test this hypothesis using male territory choice experiments. When allowed to choose between two otherwise identical territories either containing eggs fertilized by another male or with no eggs, males spent significantly more time at territories with eggs. This demonstrates that competition for mating territories is not the primary factor explaining the existence of allopaternal care in the tessellated darter. Instead, males of this species may exhibit allopaternal care to dilute predator pressure on their own eggs or because females prefer to mate with males whose territories contain eggs.

We determined seasonal foraging modes of four sympatric darter species, Etheostoma lynceum, E. stigmaeum, E. swaini and Percina nigrofasciata, from Beaverdam Creek, Mississippi (USA) at two scales of taxonomic resolution: (1) chironomid prey identified to family and (2) chironomid prey identified to genus/species. When chironomids were identified to family, high proportional similarity (PS) and low niche breadth (NB) values suggested the darters fed opportunistically on a relatively small number of available prey taxa. In contrast, when chironomids were identified to genus/species, concordant low PS and NB values suggested the darters fed like classic specialists, selecting a small number of prey taxa relative to prey availability in the resource base. The darters selected just one to four chironomid taxa from 52 available taxa across seasons. Our study shows that the scale of taxonomic resolution used to identify darter prey may influence the characterization of darter foraging modes.

The channel darter, Percina copelandi, is a small benthic fish with a wide but disjunct distribution across central North America. The development of conservation and recovery strategies for Canadian populations is limited by a lack of knowledge regarding ecology, population size and other factors that affect its distribution and abundance. We sampled five rivers in the Lake Ontario basin to test whether the distribution of P. copelandi reflected riffle habitat characteristics or landscape-scale factors such as surficial geology and natural barriers (waterfalls). At most sites yielding P. copelandi, riffles flowed into deep sand bottomed run or pool habitats. Despite a lack of association with local surficial geology or riffle habitat characteristics, both the upstream limits of P. copelandi occurrence and distribution of suitable habitats reflected the distribution of waterfalls, chutes and bedrock outcroppings. In contrast to P. copelandi, distributions of Etheostoma flabellare, P. caprodes and Rhinichthys cataractae reflected among site differences in riffle habitat.

We examined channel and point bar changes over time in the Pearl River, a meandering, Coastal Plain stream in Mississippi and Louisiana. We interpreted extreme changes in bar area as evidence of channel instability and related this to the diversity and abundance of darters in the river. Darters were less diverse and abundant in more disturbed reaches in comparison with relatively undisturbed reaches. Darter abundance was positively correlated with proximity to extreme bar-area changes. The relationship between channel instability and darter abundance observed here points to the importance of landscape level approaches to in-stream habitat management. The results suggest that river management practices that prevent or mitigate extreme changes in channel or sediment dynamics should be adopted for the benefit of benthic communities.

In two laboratory experiments we tested juvenile yellow perch, Perca flavescens, for behavioural responses to alarm cues of injured conspecifics and several prey guild members: adult perch, Iowa darters, Etheostoma exile and spottail shiners, Notropis hudsonius. Spottail shiners are phylogenetically distant to yellow perch whereas Iowa darters and perch are both members of the Family Percidae. Groups of juvenile yellow perch increased shoal cohesion and movement towards the substrate after detecting conspecific alarm cues when compared to cues of injured swordtails, Xiphophorus helleri, a species phylogenetically distant from perch. Individual juvenile perch increased shelter use and froze more when exposed to chemical alarm cues from both juvenile and adult perch, shiners and darters compared to exposure to injured swordtail cues or distilled water. The response to cues of darters may indicate that alarm cues are evolutionarily conserved within percid fishes or that perch had learned to recognize darter cues. The response to spot tail shiners likely represents learned recognition of the cues of a prey guild member.

Local, short-term dispersal by the U.S. federally-threatened leopard darter, Percina pantherina, was examined in the field and in the laboratory to assess the possible effects of natural versus man-made barriers on movement. Mark-resight studies were conducted in two summers at sites in the Glover River (southeastern Oklahoma, U.S.A.). At one site, patches of 'preferred' habitat were separated by a natural riffle; at the other site, by a low-water road crossing with culverts. At the Natural Riffle site, darters moved downstream across the riffle, but also moved upstream into deeper water when water temperatures exceeded 29°C in the `preferred' habitat. Use of deeper, cooler waters by this species in late summer suggests that thermal refugia may be important habitats for the long-term management of leopard darters. At the Road Crossing site, all documented movement was in a downstream direction, and at least two darters traversed culverts in the low-water bridge. Laboratory studies of movement across several types of culverts suggested that culverts significantly decrease the probability of movement among habitat patches.

The distribution of the swim bladder was examined in 20 species representing all four genera (Percina, Etheostoma, Crystallaria, and Ammocrypta) of darters (Etheostomatini). Including data on species examined in other studies, swim bladders have been found in 15 of 17 species of Percina, but were absent in Crystallaria asprella, Ammocrypta pellucida, and the 18 species of Etheostoma examined. Relative swim bladder length in Percina was shown to be positively correlated with body size. Although not statistically significant, swim bladder size also correlates with habitat (riffle, run, or pool) and swimming behavior (midwater or benthic).

We describe eight tetra-nucleotide microsatellite markers for the leopard darter (Percina pantherina), a federally threatened percid fish endemic to Oklahoma and Arkansas. We tested these markers on 42 individuals from two localities and provide summary statistics on population variability. Eight loci yielded 2–12 alleles per locus. These markers contribute to the availability of markers for programs aimed at monitoring and managing the genetic resources of P. pantherina and related taxa.

Much has been written about the influence of exotic or nonindigenous species on natural habitats and communities of organisms, but little is known of the physical or biological conditions that lead to successful invasion of native habitats and communities by exotics. We studied invasivity factors in headwater streams of the Susquehanna River West Branch, which drains portions of the northern Appalachian Plateau. A replicated (two major tributaries) 3 × 3 factorial design was used to determine landscape effects of size (stream order) and quality (land use) on abiotic (physical and chemical) and biotic (fish community structure and function) stream attributes. Seven (21%) of thirty-four fish species (brown trout, common carp, mimic shiner, bluegill, smallmouth bass, fantail darter, and banded darter) collected in the eighteen streams sampled were nonindigenous to the basin. Watershed size (stream orders 1, 3, and 5) significantly affected stream geomorphologic and habitat variables (gradient, width, depth, current velocity, diel water temperature, bank overhang, canopy cover, and woody debris density) but not water-quality variables, while land use in watersheds (conservation, mining, and agriculture) significantly affected measured water-quality variables (alkalinity and concentrations of manganese, calcium, chloride, nitrate, and total dissolved solids) but not stream physical or habitat quality. Both watershed size and land use affected fish-community variables such as presence of particular species, species density, species diversity, tolerance diversity, and mean fish size, but in both cases the effect was transparent to native-origin status of fish species. No relationships were found between occurrence of nonindigenous species in watersheds and trophic structure or functional diversity. Therefore, the hypothesis that reduced species diversity increases vulnerability to nonindigenous species was not supported. However, the spatial variation associated with both water-quality and habitat-quality factors was greater in streams with mixed (those with nonindigenous species) than with exclusively native assemblages. These findings suggest that the mechanism for successful invasion by nonindigenous or exotic species is through change in water or habitat quality associated with human or natural disturbances, such as agriculture and mining activities in watersheds. Biotic factors appear to play no or a lesser role in the invasibility of northern Appalachian lotic systems.

Although benthic insectivorous fishes such as darters and sculpins represent a significant component of riffle communities, few studies have compared the habitat use of these non-related but ecologically similar fishes. The objectives of this study were to examine the habitat use of Etheostoma olmstedi (tessellated darter) compared to Cottus bairdi (mottled sculpin) in Nescopeck Creek and Cottus cognatus (slimy sculpin) in Jack's Creek, Pennsylvania through underwater observation. Etheostoma olmstedi occupied habitats with significantly deeper waters than those available, whereas adult and young of the year Cottus occupied habitats with significantly faster water velocities than those available. Canonical discriminant analysis revealed microhabitat partitioning between E. olmstedi and each Cottus species. Cottus bairdi and C. cognatus occupied significantly shallower habitats with faster water velocities than E. olmstedi. Sculpin species were observed most frequently under substrate whereas E. olmstedi occurred most frequently on the top surface of the substrate. Hurlbert's standardized niche breadth values indicated that C. bairdi and C. cognatus were habitat specialists with regard to water velocity measures, but exhibited generalistic patterns of depth and substrate size use. Etheostoma olmstedi was a habitat specialist with respect to depth, but exhibited generalistic patterns of resource use for substrate size. Differential habitat use by these benthic fishes is consistent with the hypothesis that resource partitioning facilitates species coexistence among stream fishes.

Species recovery efforts generally focus on in situ actions such as habitat protection. However, captive breeding can also provide critical life history information, as well as helping supplement existing or restoring extirpated populations. We have successfully propagated nine species in captivity, including blackside dace, spotfin chubs, bloodfin darters, and boulder darters. Threatened blackside dace, Phoxinus cumberlandensis, were induced to spawn in laboratory aquaria by exposing them to milt from a reproductively mature male stoneroller, Campostoma anomalum or river chub, Nocomis micropogon. The latter are nest-building minnows, with which Phoxinus may spawn in nature. Eggs are broadcast among gravel and pebbles. Blackside dace individuals reared in captivity were used for translocation. Threatened spotfin chubs, Cyprinella monacha, fractional crevice spawners, deposited eggs in laboratory aquaria in the spaces created between stacks of ceramic tiles. Captively produced spotfin chubs were used as part of a larger stream restoration and fish reintroduction project in the Great Smoky Mountains National Park. The bloodfin darter, Etheostoma sanguifluum, was first used as a surrogate to develop techniques for spawning a closely related species, the endangered boulder darter, E. wapiti. Both darter species mated in a wedge created between two ceramic tiles. Our efforts have had variable but generally high success, with survival rates of 50–90% of eggs deposited. Captive production of nongame fishes can aid recovery of rare species or populations, aid in watershed restoration, and can help to refine water quality standards. In addition, captive breeding allows discovery of important behavioral or life history characteristics that may constrain reproduction of rare species in altered natural habitats.

Microhabitat use and habitat partitioning for 10 darter species (Percidae: Etheostomatini) were studied by direct observation (snorkeling) at five sites in the Elk River drainage, West Virginia, U.S.A. We used canonical discriminant analysis and univariate tests to determine microhabitat variables that were important in segregating species. Darter species were segregated by depth, substrate size, and water velocity. In addition, Percina typically occurred in the water column, whereas species of Etheostoma were benthic and segregated by occurring under, between, and on top of rocks.

The biology, microhabitat use and migratory behaviour of the greenside darter, Etheostoma blennioides, was studied at the Mannheim Weir on the Grand River, Ontario during the summer of 1995 and 1996. Officially listed as vulnerable in Canada, greenside darters reached maturity at age 1 and lived up to 4 years. They were found in riffle habitats that consisted of cobble and loose boulders, with large mats of Cladophora. This type of unembedded substrate is uncommon in the Grand River watershed. However, local abundance of greenside darters immediately downstream from the Mannheim Weir was likely due to high water velocities from weir discharge, freshets and ice scour which help maintain unembedded riffle areas. Trap data indicated that greenside darters temporally partition this habitat with the stonecat, Noturus flavus. Other darter species were not commonly found in areas with greenside darters, whose depth selection and habitat choices were influenced by predators and morphology. Denil fishways at the Mannheim Weir rarely passed greenside darters due to prohibitively high water velocities and exclusion by larger fish.

We studied variation in clutch and egg size of the banded darter, Etheostoma zonale, using museum specimens representing three geographically separated populations from central and northern Arkansas. We found significant differences in standard length-adjusted mean clutch size and mean ovum mass. Clutch size varied by more than three hundred percent between sites, and egg mass by approximately twenty percent, demonstrating that comparative studies of interspecific variation in life history based upon a single population for each species may be misleading.

Common name: Diamond Darter. Conservation status: Listed as a “species of special concern” by West Virginia Division of Natural Resources. Extirpated from Tennessee (Etnier and Starnes 1993), Kentucky (Burr and Warren 1986), and Ohio (Trautman 1957). Systematics: Sister species of Crystallaria asprella (Wood and Raley 2000; Morrison et al. 2006). Identification: C. cincotta is overall translucent with silvery white ventral side of the body and head and four wide olive-brown saddles on the back and upper side. Preorbital blotch and 12–14 mid-lateral blotches along side (Welsh and Wood 2008). Longest known individual is 77 mm SL (Welsh and Wood 2008). D1 11–13 (12), D2 11–15 (13), A I, 11–13 (13), lateralline scales 83–93 (87), cheek scale rows 1–4 (2), opercle scale rows 1–4 (2). Pelvic fins with falcate posterior margin. Drawing by SAW, 75 mm SL male, Elk River, WV. Distribution: Extant population in the Elk River of Kanawha River drainage, WV (Cincotta and Hoeft 1987; Welsh and Wood 2008). The range previously included the Muskingum River, OH, Ohio River, OH, Green River, KY, and the Cumberland River drainage, KY and TN. Abundance: Rare, known from 12 individuals (Welsh and Wood 2008). Habitat and ecology: Collected from riffles and pools with

Common name: Maryland darter. Conservation status: Federally endangered (U.S. Fish & Wildlife Service 1967), critical habitat designated 29 August 1984 (U.S. Fish & Wildlife Service 1984). Also considered endangered by the State of Maryland. Identification: Diagnosed from all other darters by an asymmetrical caudal fin base and broad head, and from members of the subgenus Etheostoma by a short flattened genital papilla in females and narrowly connected branchiostegal membranes (Page 1983). No other darter on the middle Atlantic Slope has four dark, forwardly directed, oblique saddles across the back and incomplete dark bars of pigment on the lower half of the body below the lateral line (Knapp 1976). Maximum length 70 mm SL. Distribution: Known only from three sites in the vicinity of the Fall Line, at head of Chesapeake Bay. Described from a single specimen taken in Swan Creek in 1911. In 1965 E. sellare was also found in Swan Creek and its largest tributary, Gasheys Run. All recent records (post 1965) are from the lower-most riffle on Deer Creek, immediately above its confluence with the Susquehanna River in Harford County, Maryland. Prior to impoundment by Conowingo Reservoir in 1928, the mainstem Susquehanna River in this area was characterized by rocky shoals and ledges, with many shallow raceways and runs, which likely would have provided optimal habitat for E. sellare. Abundance: During 1965, 110 specimens were taken from the Deer Creek population. This species has not been found in such numbers since, and no specimens have been observed since 1989, despite extensive recent survey efforts (Raesly, pers. comm. and Maryland Biological Stream Survey). Habitat and ecology: The riffle on Deer Creek that supported the largest known population ranges from 12 to 25 m wide, with rubble near the head of the riffle and increasing amounts of silt and gravel toward the sides and foot. Rooted aquatic plants, mostly Podostemum ceratophyllum, are seasonally abundant. Swan Creek and Gasheys Run are much smaller streams with a limited amount of suitable habitat. Swan Creek is now severely degraded with extensive silt deposits. Diet of 35 individuals taken on 10 November 1965 included large numbers of snails (Knapp 1976). The only other darter taxa known to consume snails in quantity are the members of the Percina subgenus Imostoma. The broad head and wide gape of E. sellare may facilitate ingestion of snails. Reproduction: Spawning is believed to occur in late April or early May (Knapp 1976). Females develop a swollen white pad on the urogenital papilla, while the male papilla is short and shows little seasonal variation. Nuptial tubercles are not developed. Threats: Urban/suburban development related to proximity to the Baltimore–Philadelphia metropolitan complex, with associated changes in sediment and nutrient loading, flow and thermal regimes. Observed declines during the 1980s were correlated with increased sediment deposition (Raesly, pers. comm.). Impoundment of Conowingo Reservoir (and subsequent manipulation of flows downstream) reduced potential habitat in the mainstem Susquehanna. Introduced populations of E. blennioides and E. zonale have recently expanded in the lower Susquehanna drainage, and may compete with E. sellare for resources. Conservation action: Maryland DNR and the U.S. Fish & Wildlife Service have implemented a recovery plan (U.S. Fish & Wildlife Service 1985) with goals of managing streamside buffer zones to reduce sedimentation and agricultural pollution, maintenance and improvement of water quality. Intensive surveys of the basin have not documented specimens since 1988. The last remaining habitat that has not been thoroughly surveyed is the mainstem Susquehanna River below Conowingo Reservoir. The extreme flow fluctuations produced by Conowingo Reservoir make this habitat difficult to sample effectively. Survey work in the mainstem should be a top priority. Recent efforts to delist the darter are ill-founded without additional survey work.

Common names: Perca (dardo, dardito) de toba (S), Perca (dardo, dardito) de Cuatro Cienegas (S), Tufa darter (E). Conservation status: Endangered (Williams et al., 1989), listed as ‘dardo de Cuatro Cienegas, Etheostoma sp.’ which confounded this darter with E. segrex Norris & Minckley (1997). Identification: Small darter, rarely exceeding 35 mm SL. Seven pairs of branchiostegal rays. Nuptial males with orange dorsal and anal fins, scattered orange spots on body and blue throat. Photograph by SMN, adult male (above) and female (below). Distribution: Restricted to the spring fed and formerly isolated Rio Mesquites drainage in western Cuatro Cienegas basin in Coahuila, Mexico, in southern headwaters of the Rio Salado de los Nadadores, tributary to Rio Bravo del Norte (Rio Grande). Abundance: There are no hard data regarding abundance. Tufa darters occur in low densities in preferred habitat. Habitat and ecology: This species occupies unvegetated bottoms of gravelto cobble-sized fragments of tufa and tufa stromatolites. Natural channels where E. lugoi has been observed and caught are from 1.5 to 15 m wide and 30 cm to 1.2 m deep with moderate currents. Tufa darters feed on invertebrates. This small darter is remarkably cryptic in its preferred habitat. Reproduction: Little is known. Nuptial males have been collected and apparent spawning acts observed in April (Norris & Minckley 1997). Threats: Natural range of the tufa darter is highly restricted (one of the smallest natural ranges for any darter), in habitat dependant on consistent spring flow. Habitat in significant portions of its range is relatively intact; however, water extraction for human use (both through wells and canals) remains the prime threat. In August 1996, the cichlid Hemichromis guttatus was first observed in an isolated system in the basin and has since been spreading (D.A. Hendrickson & M. Stephens personal communication, Contreras-Balderas 2001). This indefensible and inexplicable introduction underlines the constant danger from alien organisms faced by inhabitants of isolated systems such as those in the Cuatro Cienegas basin. Conservation action: The floor of the Cuatro Cienegas basin, including all the aquatic systems, has been designated as a biological preserve (Secretaria de Desarrollo Social 1994); this may alleviate some potential threats. Conservation recommendations: An ecological and status survey must be conducted to determine distribution and life history-parameters of this darter. Lacking specific data, current water quality and flow levels should not be altered. Introduction of alien organisms must be halted. Remarks: The western Cuatro Cienegas basin – a series of formerly independent spring-fed systems – holds a diverse and highly endemic aquatic fauna (including fishes, molluscs and crustaceans) (Minckley 1992 and works cited therein). Basin inhabitants are threatened by careless development within the basin, particularly extraction of its water resources and introduction of exotic species.

The early development of rainbow darter, Etheostoma caeruleum, was examined from an ecological perspective. Steps and thresholds of ontogeny to completion of body squammation are defined, and related to environmental factors. Rainbow darter eggs are about 2 mm diameter, considerably larger than those of related logperch (Percina caprodes). The embryonic vitelline respiratory plexus is much more extensive. The pelagic interval characteristic of logperch and ancestral percids is eliminated and onset of exogenous feeding is delayed. The larger larvae of the rainbow darter can begin feeding directly on aquatic insects, and complete their life cycle in streams. Therefore, shifts in the timing of important thresholds (e.g. exogenous feeding) are ecologically important. Furthermore, early maturation and/or delayed bone and scale formation may be responsible for reductions in the lateralis system and scalation in this and other darter species.

During 1982 and 1983, seining, fyke netting, and SCUBA observation were used to determine the depth distribution, abundance, and mortality of small littoral-zone fishes (bluntnose minnows, shiners [primarily mimic shiners], yellow perch, logperch, johnny darters, Iowa darters, and mottled sculpins) in Sparkling Lake, a small moderately-productive lake in northern Wisconsin. During the summer cyprinids, darters, and mottled sculpins were most abundant in areas shallower than 1 m, while yellow perch were most abundant at depths of 2 to 4 m. Between August and October cyprinids and yellow perch moved to water 1 to 2 m deeper, while the depth distributions of darters and mottled sculpins generally remained unchanged. Large within- and between-year variations in abundances and mortality rates were evident for all species. In 1982, most of the mortality of cyprinids and darters occurred during a short period in late spring and early summer, with relatively little afterwards. In 1983, this pattern was reversed for cyprinids and Iowa darters, but not logperch and johnny darters. Between-year differences in abundance were greatest for young-of-the-year yellow perch; they were 400 times more numerous in 1983 than in 1982. Darters had their lowest mortality rates and highest reproductive success in 1983, while the opposite was true for cyprinids. This lack of synchrony between darters and cyprinids suggests that these two taxa responded differently to changes in environmental conditions in Sparkling Lake. Predation may have accounted for much of the variability in darter population parameters, but appeared to be a less important source of variation for cyprinid population parameters.

Large male tessellated darters, Etheostoma olmstedi, defend flat-bottomed rocks, the undersides of which serve as spawning substrates. Because females attach eggs directly onto bare stone, a spawning bout necessarily decreases the surface area available for further breeding at a nest. In apparent response to the female preference of ovipositing on rocks with the most bare surface, fathers abandon nests with their attached offspring to search for rocks with more uncovered surface. Egg abandonment also results after roving fathers intercept and spawn with ripe females and remain at a different rock to care for a new clutch. In essence, large males appear to maximize the number of eggs they fertilize by sequentially monopolizing breeding patches that are temporarily most desirable to females. The costs to a father of abandoning his eggs appear to be low for two reasons: (1) non-territorial males, created by a scarcity of suitable rocks, readily occupy vacant nests, and clean and aerate the abandoned eggs; and (2) after water hardening, eggs are less vulnerable to cannibalism. The maintenance of eggs by nonparental males may be both incidental to scrubbing the ceiling for their own breeding and adaptive in that viable eggs stimulate females to spawn; neither would appear to involve parental investment costs. Thus, allopaternal care in the tessellated darter may have evolved because it is performed in the selfish pursuit of spawning opportunities while entailing little, if any, of the costs normally subsumed within parental investment.

Aggression by nest-guarding male johnny darters, Etheostoma nigrum, against intruding crayfish was investigated in laboratoy experiments and field observations. In the laboratory, darter success in chasing crayfish, Orconectes rusticus, from the nest site was inversely related to crayfish size. Small crayfish (less than 15 mm carapace length) were routinely evicted from the nest area by nips directed at the posterior end of the abdomen. Although such aggressive behavior was less successful against larger crayfish, even the largest crayfish tested (carapace length 30–32 mm) were chased from the nest area in 33% of the trials. Those large crayfish that entered nests often remained despite repeated attacks by the male johnny darter and egg predation was observed. In a small Ohio stream, openings to johnny darter nests were generally between 7 and 13 mm. Thus crayfish with a carapace height greater than 13 mm (corresponding to a carapace length greater than 29 mm) would not be able to enter johnny darter nests. In field observations, male Johnny darters successfully defended nests against another crayfish species (Orconectes sanborni, carapace length 12–29 mm). Together, aggressive behavior and small size of nest entrances allow the johnny darter to successfully reproduce in areas with abundant crayfish.

Winterkill lakes often have a characteristic fish community, presumably composed of species able to survive winter hypoxia. Our research on a small winterkill lake in northern Wisconsin indicates that fishes common in winterkill lakes have behavioral adaptations for tolerating or avoiding winter hypoxia. We examined the distribution of fishes within the lake during one winter (December through May), and fish migrations into and out of the lake for two consecutive years. As DO within the lake declined in late fall, adult-sized fishes of four species, brook stickleback, finescale dace, redbelly dace, and fathead minnow, moved to the ice-water interface where DO levels were highest. Stickleback, and to a lesser extent, fathead minnows, also moved toward the more highly oxygenated water near the inlet. During the first year, young-of-the-year fishes of blacknose shiner, Iowa darter, redbelly dace, and fathead minnow, avoided hypoxic conditions by emigrating from the lake via the outlet stream in late fall and early winter while DO within the lake was still relatively high. Blacknose shiner, redbelly dace, and fathead minnow returned to the lake in spring. Almost no fishes were trapped leaving the lake in the second fall-winter season. Central mudminnows neither moved to the ice-water interface nor emigrated from the lake as DO dropped. Mudminnows survive winter hypoxia by breathing oxygen-containing bubbles trapped beneath the ice. These relatively simple behavioral adaptations allow fishes to survive or avoid hypoxic conditions lethal to other species and may help explain the consistency in fish communities of winterkill lakes.

Patterns of ecotopic variation in the population structure of two common and relatedPercina species were examined among seven central Gulf-Coast stream sites by Kendall's concordance tests, revealing four complexes of variables with significant covariation from a total of 18 population and habitat variables. The first complex comprised three interrelated habitat variables, implying that mid-stream surface current varied inversely with both instream cover and substrate heterogeneity. The second complex of five interrelated variables revealed (1) that darter abundance was better correlated with the area of instream cover than with total area, and (2) that site density [number m-2] varied inversely with site area. Along with three other variables, cover density (number per square meter of instream cover) formed a third complex, demonstrating resource complementarity between instream cover and macroinvertebrate abundance. Variables within the fourth complex all increased concomitantly with the key variable of mean darter size, including body-size diversity, biomass, relative abundance of the two darter species and mid-stream depth. Within the study region, local ecological factors largely regulate distributions, abundances and size-structures ofPercina populations, apparently even outweighing the effects of stochastic and historical factors

Predator-prey interactions were studied among a small prey fish (the johnny darter Etheostoma nigrum) and two predators (crayfish Orconectes rusticus and smallmouth bass Micropterus dolomieui) with complementary foraging behaviors. When only smallmouth bass were present, darters reduced activity to 6% of control rates and spent most of the time hiding under tile shelters. When only crayfish were present, darter activity and shelter-use were similar to controls. When both crayfish and bass were present, an interaction occurred. Darters, normally inactive in the presence of bass, were often forced to move by approaching crayfish and thus activity increased to 19% of control rates. Also, darters were often evicted from shelters by intruding crayfish. Thus, crayfish increased the vulnerability of small fish to bass by evicting them from shelters and causing increased activity. Conversely, bass increased the vulnerability of small fish to crayfish by forcing these fish to seek cover under shelters occupied by crayfish. Intimidation effects of bass on darters last for some time. After a 30-min exposure to bass, darters showed reduced activity and increased shelter use lasting at least 24 h after the bass was removed. Thus predators, throught intimidation, can influence prey behavior even though the predators are no longer present.

THESE studies comprise more or less beautiful photographic pictures of the red-headed woodpecker, Egyptian goose, sacred ibis, stone curlew (thicknee), little green-backed heron, sandpiper, rufus-necked nightjar, bateleur eagle, darter, cormorant, black and white African chats, paradise fly-catcher, hagadash ibis, whydah finch, black-headed shrike, crowned crane, and pied kingfisher. The last-named is an excellent picture. That of the crowned cranes is also of interest as showing the appearance of the immature bird at a stage not usually illustrated in museums. The red-headed woodpeckers are also fine pictures. There are some charming studies of ibis and of the little green heron on its nest with eggs; of the darters on their nests amongst the trees, and an excellent figure of their white, downy young; and a characteristic representation of the black chat with a white splash across the wing, which is such a constant and charming feature in Uganda landscapes. Studies of Bird-life in Uganda. By Dr. R. A. L. van Someren V. G. L. van Someren. (London: John Bale, Sons, and Daniellson, Ltd., 1911.) Price 1l. 11s. 6d. net.

The darter goby, Gobionellus boleosoma, sieves meiofaunal organisms from ingested sediment bites. Gut contents of darter gobies were compared with available food items as determined from core analysis. Copepods (the most numerous item in guts), and ostracods were significantly selected for by the gobies. Nematodes occurred in the same relative numbers in guts as in cores. Foraminifera (the most numerous item in cores) were significantly selected against.

The two subspecies considered in this study, E. o. olmstedi and E. o. atromaculatum, have been separated previously by characters of squamation and lateral-line scale counts. Extensive collecting and an examination of museum collections pointed out difficulties in assigning subspecific names to some populations of E. olmstedi in southeastern Virginia. This study is intended to indicate some of the practical and theoretical taxonomic problems encountered.