Centrarchid Species Research Articles

Effects of Common Carp on Reproduction, Growth, and Survival of Largemouth Bass and Bluegills

AbstractThe common carp Cyprinus carpio was introduced to North America more than a century ago, but little research has focused on interactions between this invasive species and native fishes. We used large mesocosms (600 m2) within drainable 0.4‐ha ponds to examine the effects of adult common carp on (1) reproduction of largemouth bass Micropterus salmoides and bluegills Lepomis macrochirus and (2) growth and survival of the larvae and juveniles of these centrarchid species. In separate enclosures, adult bluegills or largemouth bass were stocked with or without common carp. In enclosures with common carp, turbidity was substantially higher, but both centrarchid species spawned and the densities and sizes of larval largemouth bass and bluegills were similar to those of larvae in enclosures without common carp. As juveniles grew, largemouth bass survived at a higher rate but were smaller in enclosures containing common carp compared with largemouth bass in enclosures without common carp. In a second experiment, we stocked known numbers of older juvenile centrarchids into enclosures and found decreased growth for both largemouth bass and bluegills. However, survival of largemouth bass was again higher in enclosures with common carp. Although centrarchid spawning was successful and larval growth and survival did not decrease in the presence of common carp, centrarchid growth slowed at the juvenile stage, probably due to food resource limitation resulting from direct competition with common carp for invertebrate forage, high turbidity caused by common carp, or both of these factors.

Substrate choice of territorial male Topeka shiners (Notropis topeka) in the absence of sunfish (Lepomissp.)

Abstract – Topeka shiners (Notropis topeka), an endangered minnow species, typically spawn on or around breedingLepomissunfish (Centrarchidae) nests. Why spawning Topeka shiners are attracted to these nests is unclear, but having the nesting sunfish provide shiner eggs with improved aeration, a lessening of siltation, and protection from egg predators are possibilities. We tested the substrate utilisation of Topeka shiners in outdoor tanks in the absence of sunfish to determine the shiner’s fundamental choice. Shiners were provided with substrate patches of cleaned sand, small gravel, large gravel, and small cobble, and the bare floor of the tank. The substrate above which a male shiner established his territory was used as evidence of choice. A statistically significant choice for sand substrates was demonstrated. This fundamental choice might influence which sunfish nests Topeka shiners use, given that nest substrate characteristics differ both between sunfish species and within species by spawning site location.

Native Fish and Anuran Assemblages Differ between Impoundments with and without Non-Native Centrarchids and Bullfrogs

Abstract Centrarchids (sunfish and bass species) and Bullfrogs (Lithobates catesbeianus) have been introduced into aquatic systems around the world and have the potential to negatively impact native fish and anurans. We surveyed fish and anuran assemblages from 26 impoundments in the New Jersey Pinelands, USA. We excluded non-native species and used ordination analysis to generate four native-species community gradients based on native-fish and anuran presence–absence and abundance data. All four community gradients paralleled an increase in the percentage of upstream-altered land (development and upland agriculture) and an increase in either non-native-centrarchid richness or abundance. Based on presence–absence and abundance data, native-fish and native-anuran assemblages, including restricted species (those generally limited to the Pinelands region) and widespread species (those widely distributed in New Jersey), differed between impoundments with and without non-native centrarchids. Compared to widesp...

Parental care in response to natural variation in nest predation pressure in six sunfish (Centrarchidae: Teleostei) species

Abstract – Parental care is an important, energetically costly component of the life history of many fishes. Despite this importance, little is known about how different species of fish vary parental care in response to natural nest predator burdens. In this study, underwater videography was used to quantify parental care activity of six species of syntopic nesting male centrarchid fishes in Lake Opinicon, Ontario, in response to natural predators. This approach was used to test the hypothesis that as offspring develop from eggs to wrigglers, parental care activity should decrease or remain static for fish guarding nests with low predator burden and increase for those with high predator burden, reflecting different external risks. Principal components analysis (PCA) was used to derive common aeration and nest defence variables. Aeration and predator defence activity of the fish varied extensively among species. Parental care behaviours indicative of defence and vigilance (e.g., turning, departures, time away from nest, displays) tended to be highest for species that had the most predation attempts, although this was not entirely consistent. There was also a positive relationship between the defence PCA metric and attempted predation. Defence did not vary with stage of offspring development, although interactions between defence and developmental stage were noted for several species. A trade‐off between aeration and defence was not observed. In fact, species that provide high levels of aeration also simultaneously provide high levels of defence. Stage‐specific patterns of defence in this study were less apparent than those documented by studies using responses to staged predator intrusions making it unclear as to the extent that fish were responding to the level of the risk to offspring than to the value of the brood. Therefore, combined use of observational and experimental assessments of parental care investment may be most appropriate for refining current theoretical paradigms.

A molecular genetic examination of the mating system of pumpkinseed sunfish reveals high pay‐offs for specialized sneakers

Intrasexual variation in reproductive behaviour and morphology are common in nature. Often, such variation appears to result from conditional strategies in which some individuals (e.g. younger males or those in poor condition) adopt a low pay-off phenotype as a 'best of a bad job'. Alternatively, reproductive polymorphisms can be maintained by balancing selection, with male phenotypes having equal fitnesses at equilibrium, but examples from nature are rare. Many species of sunfish (genus Lepomis) are thought to have alternative male reproductive behaviours, but most empirical work has focused on the bluegill sunfish and the mating systems of other sunfish remain poorly understood. We studied a population of pumpkinseed sunfish (Lepomis gibbosus) in upstate New York. Field observations confirm the existence of two male reproductive strategies: 'parentals' were relatively old and large males that maintained nests, and 'sneakers' were relatively young and small males that fertilize eggs by darting into nests of parentals during spawning. The sneaker and parental male strategies appear to be distinct life-history trajectories. Sneaker males represented 39% of the males observed spawning, and sneakers intruded on 43% of all mating attempts. Microsatellite analyses revealed that sneaker males fertilized an average of 15% of the eggs within a nest. This level of paternity by sneaker males appears to be higher than seen in most other fishes, and preliminary analyses suggest that the two male reproductive strategies are maintained as a balanced polymorphism.

Evaluating the potential effectiveness of harvest restrictions on riverine sunfish populations in Georgia, USA

Abstract The effects of minimum length limits (MLLs) on bluegill, Lepomis macrochirus Rafinesque, redbreast sunfish, Lepomis auritus (Linnaeus), and redear sunfish, L. microlophus (Günther), fisheries in 13 river sections located across Georgia were evaluated. A Beverton–Holt equilibrium yield model was used to predict and compare the response of these fisheries to three MLL scenarios: 100 (i.e. no size limit), 125 and 150 mm. Model results indicated that natural mortality rates of all sunfish species examined in this study were low enough to allow harvest restrictions to be effective if growth was fast. If sunfish reached 203 mm in <4.0 years, then MLLs were generally effective in increasing size structure without decreasing yield or causing unacceptable declines in the number of fish available for anglers to harvest. Harvest restrictions resulted in minimal increases in size structure, declines in yield and a large decrease in the number of fish harvested by anglers if time to reach 203 mm was ≥ 8.0 years. Response to MLLs was more variable when fish grew to 203 mm in 4.0–6.5 years. Examination of mortality caps largely supported the results from the model, but there was indication that empirical rates of total annual mortality may have been biased high in some instances.

Temporal variation in cuckoldry and paternity in two sunfish species (Lepomis spp.) with alternative reproductive tactics

Male alternative reproductive tactics have been described in many mating systems. In fishes, these tactics typically involve a territorial male that defends a spawning site or nest and a parasitic male that uses sneaking or female mimicry to steal fertilizations from the territorial male. In this paper, we use molecular genetic markers to examine the success of males that adopt alternative reproductive tactics in two sunfishes, comprising the bluegill ( Lepomis macrochirus Rafinesque, 1819) and the pumpkinseed ( Lepomis gibbosus (L., 1758)). In sunfishes, the tactics are referred to as parental (territorial male) and cuckolder (parasitic male). We show that cuckoldry rates peak in the second trimester of the breeding season in bluegill, whereas cuckoldry rates are lowest during this period in pumpkinseed. We also show that paternity of parental male bluegill is positively correlated with body condition, but not body length or mass. No relationship between these phenotypic variables and paternity in pumpkinseed was found. We discuss the patterns of cuckoldry in relation to differences between the species in mating opportunities, parental male defence ability, and cuckolder density. Finally, we discuss how the paternity data can be used to differentiate between two mechanisms underlying the expression of alternative reproductive tactics, comprising the condition strategy and alternative strategies.

Swimming Performance of Five Warmwater Stream Fish Species

AbstractSwimming ability of fish species may help explain their persistence or absence in flood‐disturbed streams. We used two artificial stream channels with low‐complexity (smooth Plexiglas) and high‐complexity (rocks glued onto Plexiglas) substrates to determine critical swim speeds (Ucrit, cm/s) and examine flood resistance behavior of central stonerollers Campostoma anomalum, cardinal shiners Luxilus cardinalis, orangethroat darters Etheostoma spectabile, green sunfish Lepomis cyanellus, and longear sunfish L. megalotis. In the low‐complexity treatment, central stonerollers and cardinal shiners had significantly higher Ucrit than the other species, and orangethroat darters had significantly higher Ucrit than the sunfish species did. In the high‐complexity treatment, the Ucrit of central stonerollers was significantly higher than that of green sunfish, whereas those for all other species did not differ significantly. Flood resistance behavior was measured using relative velocity (i.e., a fish's chosen velocity relative to the average flume velocity). Cardinal shiners and longear sunfish chose velocities that were significantly lower than the average flume velocity in the smooth flume at Ucrit. Orangethroat darters and green sunfish chose lower‐than‐average velocities in the complex‐substrate flume at one‐half of Ucrit. No other species exhibited significant patch selection within the flume. Our results suggest that the swimming ability of central stonerollers may give them an advantage over other species during high flows in low‐complexity substrates, whereas sunfishes and orangethroat darters are better able to use high‐complexity substrates as velocity refugia during high flows.

Analyzing nested variation in the body form of Lepomid sunfishes

Phylogenetic hierarchies are often composed of younger diverging lineages nested within older diverging lineages. Comparing phenotypic variation among several hierarchical levels can be used to test hypotheses about selection, phenotypic evolution and speciation. Such hierarchical comparisons have only been performed in threespine stickleback, and so here we use a hierarchical pattern of divergences between near-shore littoral and off-shore pelagic habitats to test for selection on the evolution of body form in Lepomis sunfish in lakes. We compare variation in external body form between fish from littoral and pelagic habitats at three levels: among ecomorphs within individual lake populations (intrapopulation), among populations of the same species in different lakes (interpopulation), and between bluegill and pumpkinseed sunfish species (interspecifically). Using geometric morphometric methods, we first demonstrate that interpopulation variation in mean body form of pumpkinseed sunfish varies with the presence of pelagic habitat. We then incorporate these results with existing data in order to test the similarity of phenotypic divergence between littoral and pelagic habitats at different hierarchical levels. Parallel relationships between certain body form traits (head length, caudal length and pectoral length) and habitat occur at all three levels suggesting that selection persistently acts at all levels to diversify these traits and so may contribute to species formation. For other traits (caudal depth and pectoral altitude), divergence between habitats is inconsistent at different hierarchical levels. Thus, nested biological variation in Lepomid body form reflects a history of deterministic selection and historical contingency, and also identifies traits that likely have likely influenced fitness and so serve important functions.

Distribution of the non-native fish species, pumpkinseed Lepomis gibbosus (Linnaeus, 1758), in Turkey

The North American centrarchid species, Lepomis gibbosus (Linnaeus, 1758), is a freshwater fish native to eastern and central North America. The species is now established in at least 28 countries of Europe and in Turkey the species’ spread has been especially rapid between 2001 and 2006, with its distribution including the following areas: Kemer Reservoir, Akcay river catchment and inland waters of the Aegean and Anatolian regions. This is the first report in a new locality of the species in Asia Minor.

Nonlethal Sampling of Sunfish and Slimy Sculpin for Stable Isotope Analysis: How Scale and Fin Tissue Compare with Muscle Tissue

AbstractWe found that the sampling of tissues that do not result in the death of the fish, such as scale and fin tissue, may be substituted for muscle tissue in stable isotope analysis (SIA) of fishes. Comparisons were made between the values of δ13C and δ15N found in muscle tissue with the corresponding scale tissue of three sunfish species (bluegill Lepomis macrochirus, pumpkinseed L. gibbosus, and redbreast sunfish L. auritus) and with caudal fin tissue of slimy sculpin Cottus cognatus. The fish showed strong linear correlation in δ13C values between their nonlethally sampled scale or fin tissue and their muscle tissue (combined sunfish: r = 0.97; slimy sculpin: r = 0.84). Sunfish δ13C values were higher in scale tissue than in muscle tissue and required a correction factor for converting the scale values to the muscle values (regression equation: y = 1.1673x + 1.0531). Slimy sculpin δ13C fin and muscle values were similar and did not require a correction factor. The correlation of δ15N values between the tissues was also strong in both sunfish (r = 0.94) and slimy sculpin (r = 0.90). A correction factor was needed to convert δ15N values from scale to muscle in the three sunfish species (y = 0.8504x + 2.6698) and from fin to muscle in slimy sculpin (y = 1.2658x − 3.3234). Results of this study and other literature support the use of nonlethally sampled tissues for SIA of fish. These methods may be used for investigations of rare and endangered species and also allow for analysis of archived fish scales.

Threatened fishes of the world: Elassoma okatie Rohde and Arndt 1987 (Elassomatidae)

Conservation status: Threatened and protected by state law in North Carolina (NWRC 2004). State threatened in South Carolina (SCDNR 2003). Listed by the Federal Endangered Species Act as a species of concern, as followed by the American Fisheries Society (Williams et al. 1989; NWRC 2004). Internationally recognized as nearly threatened (Gimenez Dixon 1996). Identification: D IV/8-12; A III/5-8; C 14; P1 14-17; P2 I/5; L1 2430; mouth terminal and upturned. Lateral line absent. Sympatric species of pygmy sunfishes have head scales or humeral spots and ocular bars. Elassoma boehlkei normally has 12–14 vertical bars along the body, alternating with iridescent interbars of approximately equal width (Rohde and Arndt 1987). In the spawning season males become dark brown to black, with bright blue-green interbars. Interbars are brown and indistinct in females. Lacks humeral spots and preocular and postocular bars as seen in E. zonatum. Grows to 3.3 cm (Rohde et al. 1994). Illustration by Ellen S. Strack-Heiler. Distribution: Lumber and Cape Fear drainages of North Carolina. E. boehlkei is an associate of the evolutionarily distinct Lake Waccamaw fauna, endemic to the lake and surrounding areas (Hubbs and Raney 1946). In northeastern South Carolina a population is found in old ricefield ditches near Georgetown. Several populations occur in tributary ditches of the Waccamaw River near Conway. A genetically distinct, disjunct population occurs in the Santee drainage. Further sampling is necessary to determine distributional limits within the Santee (Quattro et al. 2001). Abundance: Irregular and localized. South Carolina populations seem stable. Populations near Lake Waccamaw (Brunswick and Columbus co., NC) seem to be in decline. At times relatively common in known habitat patches. Populations either use alternate habitats or fluctuate substantially with the seasons. Habitat and ecology: Pygmy sunfishes are generally cryptic, solitary animals. Elassoma boehlkei feeds on microcrustaceans and other small invertebrates. This species is not limited by water chemistry, as specimens are collected from M. Sandel (&) AE P. M. Harris Department of Biological Sciences, University of Alabama, Tuscaloosa, AL 35487, USA e-mail: kwksand@yahoo.com Environ Biol Fish (2007) 78:289–290 DOI 10.1007/s10641-006-9100-x

Differences in Population Metrics between Bluegill and Redear Sunfish: Implications for the Effectiveness of Harvest Restrictions

AbstractBluegills Lepomis macrochirus and redear sunfish L. microlophus were collected and aged from three reservoirs in Georgia and Alabama in 2003–2004 to describe population metrics and investigate the potential of harvest restrictions to maintain or improve the size structure of these populations. Redear sunfish grew faster and lived longer than bluegills in all three reservoirs, and estimated natural mortality was greater for bluegills than for redear sunfish; however, total annual mortality was similar between the species in two of the three reservoirs. Population dynamics models did not predict any significant benefits to bluegill size structure and yield from minimum length or bag restrictions. In contrast, redear sunfish populations in each study reservoir showed significant increases to size structure and minimal decline in yield from various harvest restriction scenarios. Because of higher mortality and slower growth in bluegills, harvest restrictions probably will not positively affect their size structure without an unacceptable decline in yield. However, our results indicated that harvest restrictions may have greater potential in managing redear sunfish populations. For redear sunfish, yield was not drastically affected by minimum length limits, but after implementation of harvest restrictions the number of larger, preferred‐length (≥230‐mm) fish could increase by over an order of magnitude in moderately to highly exploitative fisheries. Finally, results of this study have demonstrated that the common practice of managing sunfish as a homogenous group may not be appropriate, particularly if the fishery is composed of a diverse array of sunfish species that are targeted by anglers.

Relationship between Habitat and Sport Fish Populations over a 20‐Year Period at West Lake Tohopekaliga, Florida

AbstractRelationships between environmental variables and sport fish population parameters were investigated for West Lake Tohopekaliga from 1983 to 2002. Through time, the lake has undergone a process of cultural oligotrophication as indicated by reductions in nutrient and chlorophyll‐a concentrations because of improvements in wastewater treatment and the establishment of hydrilla Hydrilla verticillata in the system. With this decline in trophic state, angler catch and catch rate increased for largemouth bass Micropterus salmoides, but harvest and harvest rate decreased for black crappie Pomoxis nigromaculatus. Furthermore, the angler base of the lake shifted almost exclusively to those fishing for largemouth bass. Although angling effort for largemouth bass has increased through time with reductions in trophic state, angling effort for black crappies and sunfish species Lepomis spp. has declined. The growth of largemouth bass less than age 5 has also declined since the late 1980s, and the proportion of memorable‐sized fish in electrofishing catches decreased with decreases in total phosphorus. Areal coverage of hydrilla varied dramatically throughout this 20‐year period, and angler catch rate of largemouth bass as well as angler harvest rate of black crappies were positively correlated with hydrilla coverage. We believe the current level of nutrients and intermediate levels of vegetation (20–40%) should be maintained to balance the needs of both the angling and nonangling communities and to maximize the economic potential of the lake.

Centrarchid Assemblages in Mississippi State‐Operated Fishing Lakes

AbstractWe evaluated electrofishing catch per effort in 27 state‐operated fishing lakes in Mississippi to identify patterns of centrarchid community composition and to determine whether those patterns were related to selected environmental characteristics and to artificial nutrient enrichment. Ordination with detrended correspondence analysis recognized two major axes accounting for 77% of the variability in species ordination. Axis 1 showed a distinct separation between the body sizes of various species. A notable exception was the density of small (<30 cm) largemouth bass Micropterus salmoides, which aligned with the large individuals of other centrarchid species. This pattern suggested that through predation, high densities of small largemouth bass exerted significant control over the size structure of fish communities. Axis 2 separated species of crappies Pomoxis spp., suggesting that conditions other than strong species interactions also moderated the composition of crappies in the assemblages. However, neither lake morphometry nor watershed composition exhibited a major influence over axes 1 or 2. In small, intensively managed lakes with low habitat complexity, the regulatory importance of biotic interactions may overwhelm that of abiotic factors. Nutrient enrichment influenced community structure by changing the densities of bluegill Lepomis macrochirus and largemouth bass substantially but had a minor or no effect on other species. The management techniques used in these state‐operated lakes are usually targeted toward a particular species without adequately considering the other species within the community. Our results show that attention to community‐level interactions could provide valuable insight into factors that affect the quality of the fishery, insight that is not available through traditional population‐level assessments.

A Comparison of Fish and Aquatic Plant Assemblages to Assess Ecological Health of Small Wisconsin Lakes

ABSTRACT Biological monitoring uses assemblage structure to assess condition of ecological systems. Taxa that effectively integrate impacts within the system of interest are useful for biological monitoring, whereas taxa that do not demonstrate predictable responses can provide ambiguous or misleading indicators. We compared the effectiveness of aquatic plant and fish assemblages for biological monitoring in 16 small lakes (< 80 ha). The lakes were limnologically similar but differed in extent of lakeshore development and type of watershed land-cover. Linear regression analysis revealed that the quality of the aquatic plant community declined with increasing lakeshore development (number of dwellings per km of shoreline), which is the primary source of impacts within this group of northern Wisconsin lakes. As lakeshore development increased, we observed a decrease in the Floristic Quality Index (FQI) of a lake, number of plant species per lake, number of highly intolerant plant species per lake, and the species richness and frequency of occurrence of floating vegetation. Conversely, fish species richness, centrarchid species richness, number of small benthic fish species, intolerant fish species richness and the proportion of the total catch of intolerant and vegetative-dwelling fish were not related to lakeshore development. These results indicate that, within the range of conditions observed, aquatic plant communities are more sensitive to lakeshore development than fish communities. Neither aquatic plant species composition nor fish assemblage variables were correlated with watershed land cover types; however all the watersheds were relatively small and undisturbed. In small lakes with few fish species, aquatic plants can be used as biological indicators for monitoring ecological conditions.

Mitochondrial genomes and phylogeny of the ocean sunfishes (Tetraodontiformes: Molidae)

We determined the complete nucleotide sequences of the mitochondrial genomes for the three currently recognized species of ocean sunfish: Mola mola, Masturus lanceolatus, and Ranzania laevis (Tetraodontiformes: Molidae). Each genome contained the 37 genes as found in teleosts, with the typical gene order in teleosts. Bayesian, maximum-likelihood, and maximum-parsimony analyses were conducted with the data set comprising concatenated nucleotide sequences from 36 genes (excluding the ND6 gene) of three molids and four outgroups (three tetraodontiforms plus a caproid). The resultant trees supported monophyly of the Molidae and its intrarelationships ((Mola, Masturus), Ranzania), which were congruent with previous morphology-based hypotheses.

A provisional fish index of biotic integrity for assessing Ouachita Mountains streams in Arkansas, U.S.A.

Multimetric indices are often used to monitor aquatic-resource conditions. We used existing fish-collection data from streams to develop an Index of Biotic Integrity (IBI), which is a multimetric index, for the Ouachita Mountains ecoregion in Arkansas, U.S.A. Each fish-collection site was categorized as reference or non-reference. We examined 62 candidate IBI metrics, and selected 12 non-redundant metrics that differentiated best between reference and non-reference sites. The selected metrics were: Percent (of individuals) as Black Bass; Percent as Benthic Feeders; Percent as Centrarchids; Percent as Cyprinids; Percent as Ictalurids; Percent as Mineral, Site-Prep Spawners; Percent as Mineral, Site-Prep, Parental-Care Spawners; Percent as Simple, Mineral Substrate Spawners; Percent as Miscellaneous, Site-Prep, Parental-Care Spawners; Total Number of Centrarchid Species; Total Number of Arkansas Department of Environmental Quality (ADEQ) Ouachita Mountains Indicator Species; and Total Number of ADEQ Ouachita Mountains Key Species. We standardized each metric to score from 0 to 10 by using linear equations and threshold limits. Some selected IBI metrics had their scoring criteria adjusted to account for watershed size (i.e., stream size). We standardized the IBI to score from 0 to 100. In addition, we determined that our Percent as Black Bass and Percent as Benthic Feeders metrics contributed most to IBI scores in reference conditions, but their contributions decreased with decreasing stream conditions. Reproductive metrics contributed most in degraded stream conditions. Furthermore, we identified relations between IBI metrics and water-quality and land-use variables; some relations were counterintuitive. Unexpected relations may be random observations explained by limited ranges of land-use and water-quality variables. When select water-quality and land-use variables were included in a principal component analysis, a composite Land Use Intensity variable explained most of the model variance. Although the IBI has not been independently validated, the PCA, as well as other superficial analyses, indicated that the IBI should be able to differentiate stream conditions.

Effects of incremental increases in silt load on the cardiovascular performance of riverine and lacustrine rock bass, Ambloplites rupestris

Rock bass ( Ambloplites rupestris) are a widespread centrarchid species with both riverine and lacustrine populations. After precipitation events, rivers often carry elevated silt loads, where as lakes generally remain free from suspended silt and sediment. To examine the physiological effects of silt on rock bass, we conducted a series of experiments using fish from Lake Opinicon and the Grand River in Ontario. Ultrasonic Doppler flow probes were surgically affixed around the ventral aorta to monitor cardiovascular performance. After recovery from surgery replicated treatment groups were exposed to incremental increases in silt load (made from bentonite slurry), while cardiac output and its two components, heart rate and stroke volume, were measured simultaneously. Although both groups of rock bass responded significantly to low concentrations of silt (10 NTU), the response by riverine rock bass was rapidly extinguished by acclimation or physiological adjustment. Compensatory mechanisms to minimize cardiac (and respiratory) disruption attributable to increases in suspended silt appear to be inherent in rock bass of riverine origin. These fish appear to fully compensate for interference in gas exchange at the gill surfaces 60 min after initial exposure. In contrast, individual lacustrine rock bass were highly variable in their response to elevated silt concentrations. Changes in stroke volume and cardiac output suggested no clear compensatory mechanism or strategy to cope with increased silt levels.

Development of a Multimetric Index for Assessing the Biological Condition of the Ohio River

The use of fish communities to assess environmental quality is common for streams, but a standard methodology for large rivers is as yet largely undeveloped. We developed an index to assess the condition of fish assemblages along 1,580 km of the Ohio River. Representative samples of fish assemblages were collected from 709 Ohio River reaches, including 318 “least-impacted” sites, from 1991 to 2001 by means of standardized nighttime boat-electrofishing techniques. We evaluated 55 candidate metrics based on attributes of fish assemblage structure and function to derive a multimetric index of river health. We examined the spatial (by river kilometer) and temporal variability of these metrics and assessed their responsiveness to anthropogenic disturbances, namely, effluents, turbidity, and highly embedded substrates. The resulting Ohio River Fish Index (ORFIn) comprises 13 metrics selected because they responded predictably to measures of human disturbance or reflected desirable features of the Ohio River. We retained two metrics (the number of intolerant species and the number of sucker species [family Catostomidae]) from Karr's original index of biotic integrity. Six metrics were modified from indices developed for the upper Ohio River (the number of native species; number of great-river species; number of centrarchid species; the number of deformities, eroded fins and barbels, lesions, and tumors; percent individuals as simple lithophils; and percent individuals as tolerant species). We also incorporated three trophic metrics (the percent of individuals as detritivores, invertivores, and piscivores), one metric based on catch per unit effort, and one metric based on the percent of individuals as nonindigenous fish species. The ORFIn declined significantly where anthropogenic effects on substrate and water quality were prevalent and was significantly lower in the first 500 m below point source discharges than at least-impacted sites nearby. Although additional research on the temporal stability of the metrics and index will likely enhance the reliability of the ORFIn, its incorporation into Ohio River assessments still represents an improvement over current physicochemical protocols.