Etheostoma Flabellare Research Articles

Behavioural responses to season and adult sex ratio in the fantail darter Etheostoma flabellare

Social behaviours such as competition for mates, which can indicate the strength and direction of sexual selection, may change either directly or indirectly in response to the operational sex ratio (OSR). Field studies indicate flexibility in social behaviours in response to a changing OSR, in particular as the OSR changes across the breeding season. Remaining unclear, however, is the degree to which these behavioural changes are a direct response to an unpredictably varying OSR, or are seasonal, developing in response to seasonal cues. In this experiment, we collected cohorts of male and female fantail darters at regular intervals over the course of two full breeding seasons and placed them in artificial streams in high, moderate and low adult sex ratios (ASRs). We observed streams for 5-day periods, during which we tallied aggressive and sexually solicitous behaviours. Both male and female intrasexual aggression responded to ASR manipulations as predicted, with males increasing and females tending to decrease intrasexual aggression in response to higher male numbers. Changes in intersexual aggression rates were not correlated with changes in intrasexual rates, indicating that these two classes of behaviour varied independently of one another. Male solicitations towards females increased at moderate ASRs, but decreased when the ratio of males to females exceeded the observed natural range. Contrary to predictions, female solicitations towards males increased with increasing male numbers. Male density and hence encounter rate was a confounding factor for interpreting male-directed (but not female-directed) behaviours in response to the ASR, and furthermore negatively affected overall reproductive success. We found no evidence that competitive or solicitous behaviour responds directly to seasonal cues in Etheostoma flabellare; rather, competition over mates and solicitation of mates appear to respond directly to changes in the ASR.

Short‐Term Effects of Formalin and Ethanol Fixation and Preservation Techniques on Weight and Size of Fish Eggs

AbstractPreservative‐induced changes in the weight and size of fish eggs distort information in studies of fecundity and egg production, but the nature of changes that occur during short‐term preservation is not well understood. To determine the nature of these effects and to provide a basis for correcting for such changes after sample processing, we examined the short‐term effects of 10% formalin and 70% ethanol on eggs from gravid female white suckers Catostomus commersonii and fantail darters Etheostoma flabellare collected in two tributaries of the New River, Virginia. A sequential treatment with formalin and then ethanol was also tested to simulate effects expected in a typical fixation and preservation schedule when eggs are fixed and preserved within the fish. Formalin resulted in a significant gain (36%) in egg dry weight during the first 12 h of treatment. Ethanol had no detectable effect on egg dry weight after 9 d of fixation and preservation. Eggs that were fixed in formalin and then preserved in ethanol showed dry weights that were equivalent to those of eggs that were fixed and preserved only in ethanol, implying a reversal of the effect of formalin. We hypothesize that the action of ethanol on egg proteins unbinds the formaldehyde, with the effect of reversing formalin‐induced weight gain in eggs that have been fixed with formalin. Reductions in egg diameter were similar (∼17% after drying) between ethanol and formalin treatments, but there was an additional 5.4% shrinkage when eggs were fixed in formalin and then preserved in ethanol. In comparison with changes in egg diameter, changes in egg weight had a wider range among treatments and less variability within treatments. The experimental results indicate that egg weight is a more reliable indicator of preservation‐induced changes and a more consistent characteristic than egg diameter for comparing egg production among fishes.

Life History of the Fluted Kidneyshell Ptychobranchus subtentum

The fluted kidneyshell Ptychobranchus subtentum (Say, 1825) is a candidate for listing under the Endangered Species Act by the US Fish and Wildlife Service. Fecundity, fish hosts, and selected population demographics were determined during 2005–2006 for the fluted kidneyshell in the upper Clinch River, Hancock County, Tennessee. Females were fertilized in Aug. within a 5 d period and contained viable glochidia about 4 wk later. As the embryos began to develop, the marsupium gradually changed color from white to dark brown. Glochidia were contained within conglutinates that resemble Simuliidae pupae likely to attract benthic insectivorous fish and were held over winter and released in May. Fecundity was positively related to mussel length (r2 = 0.81) and ranged from 43,000 to 500,000 glochidia. Eight species of darters (Etheostoma spp. and Percina spp.) were infested with glochidia in the laboratory to examine potential hosts and host suitability. Juveniles transformed on bluebreast darters E. camurum and dusky darters P. sciera and previously reported hosts: rainbow darters E. caeruleum and fantail darters E. flabellare. In addition, fantail darters and rainbow darters were infested with glochidia from two river systems. The median time of glochidial metamorphosis did not differ significantly between the two mussel populations. The observed ratio of adult females to males (1.9∶1) in the Clinch River differed significantly from 1∶1. Based upon thin-sections, individuals live to at least 26 y and females become sexually mature at age five.

Living on the bottom: Kinematics of benthic station‐holding in darter fishes (Percidae: Etheostomatinae)

Darters represent a substantial radiation of freshwater fishes that live in close association with the substrate in North American streams and rivers. A key feature of any darter species is therefore its ability to stay in place or to "hold station" in flowing water. Here, we quantify the station-holding performance of two morphologically divergent darter species, the fantail darter Etheostoma flabellare and the Missouri saddled darter Etheostoma tetrazonum. We also characterize the primary kinematic responses of the two species when holding station in flow speeds ranging from 4 to 56 cm s(-1) in a flow tank on either plexiglas or small rock substrate. We then present a series of hypotheses about the potential hydrodynamic and functional consequences of the observed postural changes and the links among morphology, posture, and station-holding performance. On both substrates, E. tetrazonum was able to hold station at higher flow speeds than E. flabellare. On rocks, E. tetrazonum slipped at an average speed of 55.7 cm s(-1) whereas E. flabellare slipped at 40.2 cm s(-1). On plexiglas, E. tetrazonum slipped at an average speed of 24.7 cm s(-1) whereas E. flabellare slipped at 23.1 cm s(-1). We measured body and fin positions of the two species from individual frames of high-speed video while holding station on rocks and plexiglas. We found that on both substrates, the two species generally exhibited similar kinematic responses to increasing flow: the head was lowered and angled downward, the back became more arched, and the median and caudal fin rays contracted as water flow speed increased. The ventral halves of the pectoral fins were also expanded and the dorsal halves contracted. These changes in posture and fin position likely increase negative lift forces thereby increasing substrate contact forces and reducing the probability of downstream slip.

Taxonomic Status of Etheostoma brevispinum, the Carolina Fantail Darter (Percidae: Catonotus)

Etheostoma flabellare has long been recognized as a geographically variable, polytypic species that contains undescribed species-level diversity. As the first phase of a long-term study, morphological comparisons were made on one historically recognized subspecies, E. f. brevispinum, to examine variation and determine its distribution and taxonomic status within the E. flabellare complex. Examination and analyses of meristic, morphometric, and pigmentation variables from nine river drainages (Atlantic Slope and Mississippi River Basin) revealed that Etheostoma brevispinum, the Carolina Fantail Darter, is diagnosable based on a combination of characteristics and is restricted to the Savannah, Santee, and Yadkin (upper Pee Dee River) rivers of North Carolina, South Carolina, and Virginia. Data do not support recognition of New and Roanoke River populations of E. flabellare as intergrade zones between E. brevispinum and E. flabellare as previously suggested. A potential contact zone between E. brevispinum and other forms of the E. flabellare complex was identified in the Pee Dee River; however, no intermediate populations suggestive of an intergrade zone were identified.

Responses of Three Darter Species (Genus Etheostoma) to Chemical Alarm Cues from Conspecifics and Congeners

Several species of darters of the genus Etheostoma possess a chemical alarm substance, but it is not known how widespread this substance is within the genus. We performed behavioral bioassays on Fantail Darters (E. flabellare), Rainbow Darters (E. caeruleum), and Redfin Darters (E. whipplei). Redfin Darters reacted with a fright response upon exposure to skin extracts from conspecifics and Rainbow Darters. Rainbow Darters, which are known to respond to conspecific extracts, responded to skin extracts from Redfin Darters. Neither Rainbow Darters nor Redfin Darters showed a significant response to Fantail Darter extract, and Fantail Darters did not respond to skin extracts from either congeners or conspecifics. Percid alarm substance is hypothesized to originate from epidermal sacciform cells. Histological examination of epidermal tissue demonstrated that sacciform cells were present in all three species. Our results demonstrate that chemical alarm signals are not ubiquitous for the genus Etheostoma, and that the presence of sacciform cells does not always predict the presence of the alarm response.

Movement Responses of Stream Fishes to Introduced Corridors of Complex Cover

AbstractAlthough the efficacy and design of terrestrial movement corridors have received considerable attention, the potential role of corridors in connecting stream habitats has not. We studied the movements of three benthic species of fish, fantail darters Etheostoma flabellare, riverweed darters E. podostemone, and Roanoke darters Percina roanoka, among suitable mesohabitat patches (i.e., riffles) through adjacent, less suitable pools in the South Fork Roanoke River, Virginia. We constructed movement corridors of overhead cover in four pools and compared rates of movement through these pools with those through four control pools without corridors. Movement rates were significantly greater through pools with corridors than through control pools for riverweed and Roanoke darters but equivalent through connected and unconnected pools for fantail darters. Interspecific differences in microhabitat use may have been responsible for the observed variability in corridor effects. Our results suggest that intact movement corridors can enhance the persistence of stream fish populations by connecting patchily distributed favorable habitats but that the characteristics of functional corridors may vary, even between closely related species.

Diel Periodicity of Drift of Larval Fishes in Tributaries of Lake Ontario

ABSTRACT Diel patterns of downstream drift were examined during mid-June in three tributaries of Lake Ontario. Larval fishes were collected in drift nets that were set in each stream for 72 consecutive hours and emptied at 4-h intervals. Fantail darter (Ethostoma flabellare) and blacknose dace (Rhinichthys atractulus) were the two most abundant native stream fishes and were two of the three species collected in the ichthyoplankton drift. Fantail darter larvae comprised 100%, 98.9%, and 70.2% of the ichthyoplankton in the three streams. Most larval fishes (96%) drifted at night with peak catches occurring at 2400h in Orwell Brook and Trout Brook and 0400h in Little Sandy Creek. Based on stream temperatures, peak spawning and larval drift of blacknose dace probably occurred later in the season.

Status and Life-history Aspects of Villosa constricta (Conrad 1838) (Notched Rainbow), in the Upper Neuse River Basin, North Carolina

We report the findings of stream-survey data, a length-at-age study, and host-fish determination for Villosa constricta (notched rainbow). Visual surveys were done for freshwater mussels at 44 bridge crossings in the upper Neuse River basin in North Carolina. Three surveyors, each searching a 1-m wide lane, covered a 600-m long stream reach at each site. All mussels found were identified to species and measured, and females were checked for gravidity. Of the 24 sites where V. constricta occurred, the median number found was 3.5 (range = 1-54). We cut thin- sections of 71 individual shells collected from middens at 1 survey site and counted growth lines to determine mussel age. Shell ages ranged from 3 to 14 years. Lab trials determined that Etheostoma flabellare (fantail darter) served as a suitable host for this species.

An abundance exchange model of fish assemblage response to changing habitat along embayment–stream gradients of Lake Ontario, New York

A spatially explicit abundance exchange model (AEM) was developed to predict distribution patterns of five fish species in relation to their population characteristics and habitat preferences along two embayment–stream gradients associated with Lake Ontario, New York. The five fish species were yellow perch ( Perca flavescens), bluegill ( Lepomis macrochirus), logperch ( Percina caprodes), bluntnose minnow ( Pimephales notatus), and fantail darter ( Etheostoma flabellare). Preference indexes of each target fish species for water depth, water temperature, current velocity, cover types (aquatic plants, algae, and woody debris), and bottom substrates (mud, sand, gravel-cobble, and rock-bedrock) were estimated from the field observations, and these were used to compute habitat preference (HP) of the associated fish species. Fish HP was a key variable in the AEM to quantify abundance exchange of an associated fish species among habitats on each study gradient. According to the results, the AEM efficiently determined local distribution ranges of the fish species on one study gradient. Results from the model validation showed that the AEM with its estimated parameters was able to quantify most of the fish species distributions on the second gradient. Overall, the AEM is rigorous for quantifying the distribution patterns of the target species along the changing habitat gradients. With its flexible structure that is applicable for array functions and differential equations from both static and dynamic components, the AEM can be modified to determine patterns of organism distribution in complex systems with different environments and geography.

Spatiotemporal variability of stream habitat and movement of three species of fish

Relationships between environmental variability and movement are poorly understood, due to both their complexity and the limited ecological scope of most movement studies. We studied movements of fantail (Etheostoma flabellare), riverweed (E. podostemone), and Roanoke darters (Percina roanoka) through two stream systems during two summers. We then related movement to variability in measured habitat attributes using logistic regression and exploratory data plots. We indexed habitat conditions at both microhabitat (i.e., patches of uniform depth, velocity, and substrate) and mesohabitat (i.e., riffle and pool channel units) spatial scales, and determined how local habitat conditions were affected by landscape spatial (i.e., longitudinal position, land use) and temporal contexts. Most spatial variability in habitat conditions and fish movement was unexplained by a site's location on the landscape. Exceptions were microhabitat diversity, which was greater in the less-disturbed watershed, and riffle isolation and predator density in pools, which were greater at more-downstream sites. Habitat conditions and movement also exhibited only minor temporal variability, but the relative influences of habitat attributes on movement were quite variable over time. During the first year, movements of fantail and riverweed darters were triggered predominantly by loss of shallow microhabitats; whereas, during the second year, microhabitat diversity was more strongly related (though in opposite directions) to movement of these two species. Roanoke darters did not move in response to microhabitat-scale variables, presumably because of the species' preference for deeper microhabitats that changed little over time. Conversely, movement of all species appeared to be constrained by riffle isolation and predator density in pools, two mesohabitat-scale attributes. Relationships between environmental variability and movement depended on both the spatiotemporal scale of consideration and the ecology of the species. Future studies that integrate across scales, taxa, and life-histories are likely to provide greater insight into movement ecology than will traditional, single-season, single-species approaches.

A holistic approach to taxonomic evaluation of two closely related endangered freshwater mussel species, the oyster mussel Epioblasma capsaeformis and tan riffleshell Epioblasma florentina walkeri (Bivalvia: Unionidae)

Species in the genus Epioblasma have specialized life history requirements and represent the most endangered genus of freshwater mussels (Unionidae) in the world. A genetic characterization of extant populations of the oyster mussel E. capsaeformis and tan riffleshell E. florentina walkeri sensu late was conducted to assess taxonomic validity and to resolve conservation issues for recovery planning. These mussel species exhibit pronounced phenotypic variation, but were difficult to characterize phylogenetically using DNA sequences. Monophyletic lineages, congruent with phenotypic variation among species, were obtained only after extensive analysis of combined mitochondrial (1396 bp of 16S, cytochrome-b, and ND1) and nuclear (515 bp of ITS-1) DNA sequences. In contrast, analysis of variation at 10 hypervariable DNA microsatellite loci showed moderately to highly diverged populations based on FST and RST values, which ranged from 0.12 to 0.39 and 0.15 to 0.71, respectively. Quantitative variation between species was observed in fish-host specificity, with transformation success of glochidia of E. capsaeformis significantly greater ( P , 0.05) on greenside darter Etheostoma blennioides, and that of E. f. walkeri significantly greater ( P , 0.05) on fantail darter Etheostoma flabellare. Lengths of glochidia differed significantly ( P , 0.001) among species and populations, with mean sizes ranging from 241 to 272 mm. The texture and colour of the mantle-pad of E. capsaeformis sensu stricto is smooth and bluish-white, whereas that of E. f. walkeri is pustuled and brown, with tan mottling. Based on extensive molecular, morphological and life history data, the population of E. capsaeformis from the Duck River, Tennessee, USA is proposed as a separate species, and the population of E. f. walkeri from Indian Creek, upper Clinch River, Virginia, USA is proposed as a distinct subspecies.

Influence of riffle characteristics, surficial geology, and natural barriers on the distribution of the channel darter, Percina copelandi, in the Lake Ontario basin

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.

An Ethological Analysis of the Breeding Behavior of the Fantail Darter, Etheostoma flabellare

Abstract We observed the behaviors in six fantail darter spawning events and produced a model describing the probability of any sequence of behaviors between an egg's deposition and its fertilization. Of the 12 different behaviors we observed, “quiver” and “rest” were the most common for both males and females. Courtship and spawning behaviors may be ritualized, as there was no apparent variation in how the behaviors were performed by different individuals. This could also result from a limited sample size. However, breeding pairs differed with respect to the order in which the behaviors were performed. In addition, we found that courtship behaviors occurred through all phases of the spawning events and that the largest males in the study were the only males to successfully mate with females.

Post-Impoundment Changes to the Speed River Fish Assemblage

Changes to the Speed River fish assemblage were investigated 27 years after the creation of the Guelph Lake reservoir. Electro-fishing and seine haul data collected during 2003 were compared to pre- (1975) and post-impoundment (1976 and 1978) surveys. Since its creation, the Guelph Lake fish assemblage has predictably shifted from one dominated by fluvial specialists (fantail darter and creek chub) to one dominated by habitat generalists common to lakes and reservoirs (bluntnose minnow, pumpkinseed sunfish and black crappie). Since 1975, species richness and diversity have increased at un-impounded sites along the Speed River. The occurrence of new species in Guelph Lake and upstream along the Speed River is attributed to the stocking of non-native species. Reductions in the distribution and abundance of certain fluvial specialists (fantail darter and northern hogsucker) are attributed to the flooding of riverine habitat and changes to downstream habitat conditions. Observed long-term changes to fish assemblage were not evident from earlier post-impoundment surveys.

Life history and propagation of the endangered dromedary pearlymussel (Dromus dromas) (Bivalvia:Unionidae)

The reproduction, demography, and propagation of the endangered dromedary pearly- mussel (Dromus dromas) (Lea, 1834) were studied in the Clinch and Powell rivers, Tennessee. Viable populations of the dromedary pearlymussel now occur only in the Clinch and Powell rivers; the species has been extirpated from the remaining portions of its range in the Cumberland and Ten- nessee river drainages. Females are long-term winter brooders, and they are gravid from October to June. Glochidia are contained in conglutinates that are red to white and resemble freshwater leeches or flatworms. Conglutinates are 20 to 40 mm long and are released through the excurrent aperture. Estimates of fecundity based on 7 gravid females collected from the Clinch River were 55,110 to 253,050 glochidia/mussel. The ages of 66 valves of D. dromas were determined by thin-sectioning and ranged from 3 to 25 y. Annual growth averaged 5 mm/y until age 10 and decreased to ;1.2 mm/ y thereafter. Nineteen fish species were tested for suitability as hosts for glochidia. Ten were confirmed as hosts through induced infestations of glochidia: black sculpin (Cottus baileyi), greenside darter (Etheostoma blennioides), fantail darter (Etheostoma flabellare), snubnose darter (Etheostoma simoterum), tangerine darter (Percina aurantiaca), blotchside logperch (Percina burtoni), logperch (Percina caprodes), channel darter (Percina copelandi), gilt darter (Percina evides), and Roanoke darter (Percina roanoka). Juveniles produced from these hosts were cultured in dishes held in nonrecirculating aquaculture systems containing fine sediment (,105 mm) and were fed the green alga Nannochloropsis oculata every 2 d. Survival of 2810 newly metamorphosed juveniles was 836 (29.7%) after 1 to 2 wk.

Predator Feeding Preferences for a Benthic Stream Fish: Effects of Visible Injected Marks

ABSTRACT Externally visible injected marks provide valuable information to scientists, but their presence may increase an individual's susceptibility to predation. In a laboratory experiment, we evaluated the feeding preferences of rock bass (Ambloplites rupestris) and smallmouth bass (Micropterus dolomieu) for unmarked, green-VIE-marked, and yellow-VIE-marked fantail darters (Etheostoma flabellare). Although neither predator exhibited significant selectivity for a particular treatment (ANOVA, p>0.05), smallmouth bass appeared to prefer green-marked over control or yellow-marked darters. Contrasting diel feeding strategies may explain these preferences. In a mark/recapture field study, we examined the influences of mark color and mark location on predation rate by examining variation in darter recapture rates. Again, no significant differences were detected among treatments (ANOVA, p>0.05), but dorsal-marked darters had slightly lower recapture rates than did ventral-marked ones. The effects of mark color were insignificant and opposite to those found in the laboratory study, indicating that experimental preference may not equate to increased predation rate in the wild.

Life history and population biology of the endangered tan riffleshell (Epioblasma florentina walkeri) (Bivalvia: Unionidae)

AbstractThe tan riffleshell (Epioblasma florentina walkeri) is listed by the US Fish and Wildlife Service as endangered, and is restricted to only 1 reproducing population in Indian Creek of the upper Clinch River, Virginia. We investigated its fish hosts, efficacy of infestation methods, suitability of host populations, and population demographics. Fish were collected and infested with tan riffleshell glochidia to examine potential hosts. Juveniles transformed on at least 5 of the tested species: fantail darter (Etheostoma flabellare), greenside darter (E. blennioides), redline darter (E. rufilineatum), snubnose darter (E. simoterum), and 1 or 2 cottids: banded sculpin (Cottus bairdi) or mottled sculpin (C. carolinae). Fantail darters from 4 drainages were collected and infested with glochidia to compare the suitability of various populations of the most successful host. The number of juvenile mussels obtained from fantail darters collected from Indian Creek (x ± 1 SD = 59.22 ± 10.01) was significantly ...

Landscape Determinants of Nonindigenous Fish Invasions

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.

Interspecific Competition and Qualitative Competitive Asymmetry between Two Benthic Stream Fish

The mottled sculpin, Cottus bairdi, and the fantail darter, Etheostoma flallellare, are benthic fish common in small streams over much of eastern North America. Both juveniles and adults of these two species are closely associated in low elevation headwater streams in western Virginia. I explored the effects of competition between juveniles of the two species, and the effects of heterospecific adults on juvenile performance, in a controlled, replicated experiment in artificial streams. Effects of competition were determined for three measures of juvenile performance that can be potentially related to reproductive output, and hence, to population dynamics: survival, growth and relative condition. Juveniles of C. bairdi and E. flabellare competed at densities well within the range observed in their natal streams. Adult E. flabellare had a positive effect on the survival of juvenile C. bairdi, the origin of which is unknown. Adult C. bairdi had no effect on juvenile E. flabellare. The most interesting result was that competition between juveniles of the two species was characterized by a qualitative asymmetry; C. bairdi responded with a reduction in growth, both in total length and mass, while E. flabellare responded with a decrease in relative condition, but no decrease in growth. These differences in response were clearly reflected in mass/length regressions. Unless responding variables can be precisely translated into quantitative effects on population dynamics, such qualitative asymmetries in competitive interactions greatly complicate the determination of competitive symmetry and the possible prediction of competitive outcomes, especially in species where r is difficult to determine directly.