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The current gill-based Biotic Ligand Model (gbBLM) is an acute-toxicity model used to predict site-specific safe copper (Cu) concentrations. Recent effort to develop a chronic BLM has focused on the olfactory epithelium. To further this effort, the current study looked at the effect of varying Cu concentration and exposure duration on Cu-induced olfactory dysfunction, and whether calcium (Ca) protected against Cu-induced impairment as it does at the gill. Fathead minnows (Pimephales promelas) were treated with five Cu concentrations for varying exposure durations in hard and soft water. A neurophysiological technique, electro-olfactography (EOG), was employed to determine the level of olfactory dysfunction. At the low, ecologically relevant Cu concentrations tested there was significant inhibition of EOG function; however, over time there was at least a partial recovery of olfactory function, despite the continuous Cu exposure. Calcium did not appear to protect against Cu-induced olfactory dysfunction; and even alone, Ca appeared to interfere with the olfactory response to the amino acid L-arginine. Safe copper concentrations as predicted by the gbBLM, chemosensory-based BLMs, the USEPA BLM, and hardness-adjustment equations based on the exposure waters were not entirely protective against olfactory dysfunction.

Crayfish form social hierarchies through agonistic interactions. During formation of social hier- archies, individual crayfish establish dominance by signalling status through olfaction, vision and touch. Our study investigated which of these three sensory modalities played the most impor- tant role in establishing dominance in rusty crayfish (Orconectes rusticus). Olfaction, vision and touch were systematically impaired in staged triadic and dyadic agonistic interactions to determine the relative contribution of each sensory input. Our results suggest that olfaction is the most im- portant sensory modality during the initial formation of dominance hierarchies in rusty crayfish. Using olfaction alone, crayfish were capable of communicating social status with sensory compe- tent crayfish; without full olfactory ability crayfish were unable to effectively establish dominance. Vision and touch were also found to play practical roles in reducing unnecessary risk; with anten- nae for touch, functionally reducing the number of fight initiations, and vision allowing a crayfish under imminent attack to ready itself, strike first, or retreat.

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When fish are exposed to sublethal, environmentally relevant Cu concentrations, olfactory acuity is impaired. The goals of the present study were to investigate the binding dynamics of waterborne Cu in the olfactory epithelium (OE), to examine the influence of calcium (Ca(2+)) on Cu binding, and to link Cu-OE binding to changes in olfactory acuity. Using short-term in vivo waterborne exposures to (64)Cu, we found that Cu accumulates rapidly in the OE, reaching a plateau by 3 h. The binding affinity (log K(Cu-OE)) and binding capacity (B(max)) of (64)Cu in the OE were 6.7 and 10.0 nmol Cu g(-1), respectively. As waterborne Ca(2+) was increased from 50 to 1000 muM L(-1), the B(max) of Cu decreased by approximately 50% while the log K(Cu-OE) remained constant, indicative of noncompetitive inhibition. Using electro-olfactograms (EOG), short-term exposures to 160 and 240 nmol Cu L(-1) were found to reduce olfactory responses to 10(-5) M l-arginine by 72 and 79%, respectively. Short-term exposure to 160 nmol Cu L(-1) also caused a 15-fold reduction in behavioral responses to a food stimulus. Interestingly, increasing waterborne Ca(2+) did not reduce the effects of Cu on EOG or behavioral responses. These results demonstrate that short-term, environmentally realistic concentrations of Cu not only bind to the OE of fathead minnows but also impair their olfactory sensitivity and behavioral responses to olfactory stimuli. Waterborne Ca(2+) reduces Cu-OE binding but does not protect against olfactory impairment.

In this study, we sampled yellow perch from three lakes along a metal-contamination gradient and examined their olfactory ability in response to conspecific chemical alarm cues and metal-binding characteristics of their olfactory epithelium (OE). We measured the electrophysiological response at the OE, tested their antipredator behaviour and measured neuronal density at the olfactory rosette and bulb. Yellow perch from contaminated lakes exhibited significantly larger electrophysiological responses to alarm cues than clean lake fish, but showed no antipredator behaviour contrary to clean lake fish. Neuron density did not differ at either the olfactory rosette or bulb between clean and contaminated fish. Unlike fishes raised under laboratory or aquaculture settings, fish from contaminated lakes possessed a functional OE after metal exposure, but similar to laboratory/aquaculture fishes, yellow perch did not exhibit olfactory-mediated behaviours. Thus, wild fish from contaminated lakes can detect chemical stimuli but olfactory signal processing is disrupted which could alter ecological functioning.

1.†Inducible defences may be temporary and favoured where predation is intermittent and have been demonstrated in several invertebrates and vertebrates when prey detect chemical cues (kairomones) released by predators. Daphnia pulex (a water flea) exposed to Chaoborus (midge larvae) kairomones produce small neckteeth on the dorsal surface of the head as a defence against this gape-limited predator and survive better in the presence of Chaoborus. Recent studies have shown that waterborne copper (Cu) impairs the induction of neckteeth which could lead to lower survival. 2.†Here, we examined the effects of Cu on morphological changes and shifts in life-history traits in D. pulex exposed to kairomone from Chaoborus americanus. We exposed D. pulex mothers to chemical cues of C. americanus fed on either D. pulex neonates or on brine shrimp Artemia salina, the same Chaoborus cues combined with an environmentally relevant concentration of copper (10†03BCg†L22121), or dechlorinated tap water. We examined several morphological characteristics of neonates and life-historical characteristics of adults as well as assessing survival of neonates by staging encounters with predators. 3.†Neonates from mothers exposed to kairomone plus copper had fewer and shorter neckteeth than neonates from mothers exposed to kairomone alone. Moreover, neonates exposed to Cu had lower survival during encounters with predators than neonates exposed to kairomone without Cu. 4.†Adult female Daphnia exposed to kairomones released more neonates within the first 24†h of brood release and emptied their brood pouches quicker than mothers not exposed to kairomones, irrespective of the presence of Cu. 5.†Impairment by metals of morphological defences in zooplankton could lead to a decline in population density and alter community structure.

Parental care is an energetically demanding activity that ensures genes are efficiently passed from one generation to the next. According to evolutionary theory, the greatest energetic investment should be directed towards offspring that are most closely related to the parent. Male fathead minnows, Pimephales promelas, provide this parental investment to developing embryos but not newly hatched larvae. Therefore, selection should favour recognition of embryonic kin to ensure energetic expenditure is optimally invested. In this study, adult male fathead minnows were tested using behavioural assays, with egg cannibalism as an endpoint, to determine whether adult males could discriminate between related and unrelated embryos. Egg cannibalism was highest when adult male fathead minnows were presented with unrelated eggs, and lowest when presented with eggs fertilized by the test subject (related eggs). The degree of cannibalism was also a function of breeding status. Unrelated males in breeding condition showed an intermediate response between the low cannibalism demonstrated by related males, and the high cannibalism demonstrated by unrelated males in a non-breeding condition. These results suggest that although male fathead minnows can discriminate between unrelated and related embryos, at least some component of parental investment is a simple function of breeding status.

This review summarizes some of the main findings of our work with the Metals in the Environment Research Network examining seasonal and regional effects on metal accumulation, growth, condition, and physiology in wild yellow perch (Perca flavescens ) from 10 lakes comprising two metal contamination gradients in the indus- trial regions of Sudbury, Ontario and Rouyn-Noranda, Qu ´ ebec, Canada. The specific objectives of this review are: (1) to propose threshold tissue metal concentrations to discriminate between fish from contaminated and reference sites; (2) to identify factors that can influence metal accumulation and fish condition; and (3) to define an experimental approach for measuring metal effects in wild yellow perch. Using tissue thresholds appeared useful not only for discriminating fish from clean or con- taminated environments, but also provided a simple approach to examine metabolic consequences of tissue metal accumulation. Overall, fish from Sudbury grew faster, expressed higher aerobic capacities, and died younger, but also appeared better at limiting accumulation of some metals than Rouyn-Noranda fish. The condition of the latter fish was clearly more affected by metals than Sudbury fish. Finally, our dataset allows us to propose that yellow perch are highly suitable for ecological risk assessment studies of metal effects in wild fish, but that fish size, season, and re- gion must be considered in sampling design and that several reference sites must be studied for meaningful conclusions to be reached.

Recent evidence suggests that offspring viability is related to maternal characteristics in fishes, possibly because ova quality is dependent upon these maternal traits. Provisioning of ova with particular constituents may vary with the age, size, and current condition of the female. We examined patterns of within- and among-population variation in ova concentrations of seven essential metals (Ca, Co, Cu, Fe, Mg, Mn, Zn) in four walleye (Sander vitreus) and one lake whitefish (Coregonus clupeaformis) populations. Within populations, among-female variability in ova metal concentrations was lowest for Zn (CVs 6.2-11%), and highest for Mn (CVs 26-88%). However, ova metal concentrations were not consistently related to maternal age, size, or indices of body condition. Mean ova metal concentrations varied significantly among walleye populations for five of the seven metals examined; variability was lowest for Ca and Co, and highest for Mg and Mn. Walleye and lake whitefish from the same waterbody, Lake Ontario, also differed significantly in ova metal concentrations. Lake whitefish produced ova with significantly higher concentrations of Ca, Fe, Mn, and Zn. Ova metal concentrations observed in this study were generally lower than those reported in earlier studies. Metal provisioning of ova in walleye and lake whitefish does not appear to be related to the ontogenetic or nutritional state of the female.

The antipredator responses of adult and larval fathead minnows Pimephales promelas to chemical alarm cues prepared throughout ontogeny were tested using various behavioural assays. Larval epidermis was also examined during ontogeny using standard haematoxylin and eosin staining techniques. Adults elicited an antipredator response to chemical alarm cue made from larvae as young as 8201317 days post-hatch. Interestingly, larvae did not possess visible club cells until 28201337 days post-hatch and did not respond to conspecific chemical alarm cue until 48201357 days post-hatch. These results suggest that chemical alarm cue may not be contained within club cells and that the components of larval and adult chemical alarm cue may be similar throughout ontogeny.

Rainbow trout (Oncorhynchus mykiss) are often used to estimate important biotic ligand model (BLM) parameters, such as metal-binding affinity (log K) and capacity (Bmax).  However, rainbow trout do not typically occupy metal-contaminated environments, whereas yellow perch (Perca flavescens) are ubiquitous throughout most of North America.  This study demonstrates that dynamic processes that regulate Cu uptake at the gill differ between rainbow trout and yellow perch.  Rainbow trout were more sensitive to acute aqueous Cu than yellow perch, and toxicity was exacerbated in soft water relative to similar exposures in hard water.  Whole body Na loss rate could account for acute Cu toxicity in both species, as opposed to new Cu uptake rate which was not as predictive.  Time course experiments using radiolabelled Cu (64Cu) revealed that branchial Cu uptake was rather variable within the first 12 h of exposure, and appeared to be a function of Cu concentration, water hardness, and fish species.  After 12 h, new branchial Cu concentrations stabilized in both species, suggesting that metal exposures used to estimate BLM parameters should be increased in duration from 3 h to 12+ h. In rainbow trout, 71% of the new Cu bound to the gill was exchangeable (i.e., able to either enter the fish or be released back to the water), as opposed to only 48% in yellow perch.  This suggests that at equal exposure concentrations, proportionally more branchial Cu can be taken up by rainbow trout than yellow perch, which can then go on to confer toxicity.  These qualitative differences in branchial Cu handling between the two species emphasize the need to develop BLM parameters for each species of interest, rather than the current practice of extrapolating BLM results derived from rainbow trout (or other laboratory-reared species) to other species.  Data reported here indicate that a one-size-fits-all approach to predictive modeling, mostly based on rainbow trout studies, may not suffice for making predictions about metal toxicity to yellow perch—i.e., a species that inhabits metal-contaminated lakes around northern Canadian industrial operations.

Maternal size influenced egg fatty acid profiles in Lake Ontario walleye but not in those from Lake Winni- peg. Maternal somatic parameters had few predictive influences on egg metal concentrations and these were not consistent between the populations.

The influences of metal contamination, fish size, season, and region on tissue metabolic capacities and protein concentrations were examined in yellow perch from two metal gradients (Sudbury, Ontario, and Rouyn-Noranda, Qu ´ ebec, Canada) in two seasons (spring and summer). In general, increased tissue Cu and Cd contamination was associated with lower aerobic capacities, suggesting direct metal inhibition of aerobic enzymes. However, our data also revealed that tissue Ni contamination positively affected aerobic capacities, possibly due to oxidative damage to mitochon- drial membranes leading to compensatory increases in the activity of mitochondrial enzymes. Tissue aerobic capacities decreased, but anaerobic capacities increased, with size. Tissue protein concentrations and metabolic capacities were also influ- enced by season. A novel finding of this study is that size-corrected tissue enzyme activities can differ markedly in yellow perch sampled in the same season in similar lakes, but separated by a few hundred kilometers. Overall, the results from this large dataset support that tissue metabolic capacities are under seasonal and regional influences, but are also affected by metal contamination. Our study indicates that tissue metabolic enzyme activities should be considered as a tool for ecological risk assessment studies aiming at detecting metal stress in wild fish. However, fish should be sampled over a short period, and reference sites should be close to contaminated sites.

Wild yellow perch (Perca flavescens) were sampled from five lakes in each of two metal contamination gradients in Sudbury, ON (n = 1324) and Rouyn-Noranda, QC (n = 1125) in the spring and summer of 2002 and 2003, respectively, in order to examine growth patterns, longevity, and the single and combined influences of season, region, and position along each metal contamination gradient on fish condition. Growth patterns varied by contamination gradient; fish from Rouyn-Noranda began rapid growth at a young age, whereas fish from Sudbury lakes showed slow growth rates between ages 0-3, after which growth rates improved. Slopes of double-log plots of fish weight and lengths varied between the two study regions when all fish were considered together and when the analysis was restricted only to non-contaminated reference lakes. Fish from contaminated lakes grew faster and died younger than fish from reference lakes in both contamination gradients. Observed growth patterns are likely due to increased food consumption in metal-contaminated lakes, as a compensatory means of replacing lost electrolytes from chronic metal exposure. Fish from Sudbury had lower condition than those from Rouyn-Noranda, higher condition occurred in the summer than in the spring, and fish from contaminated lakes had lower condition than those from cleaner lakes. However, when condition was studied at the level of individual lakes within each contamination gradient, condition variability was too high to draw any meaningful conclusions. Tissue Zn accumulation appeared to correlate with fish condition. However, tissue Zn concentrations demonstrate strong temporal stability, and it is more likely that Zn covariates, such as Cd or Cu (both of which are much less temporally stable in fish tissues) actually influenced condition. These results suggest that long-term processes are more important than short-term processes for establishing growth patterns, longevity, and fish condition in metal-contaminated systems.

This study examined relationships among water, sediment, diet and fish tissue metal (Cd, Cu, Ni, Se and Zn) concentrations in yellow perch from metal gradients in two regions (Sudbury (S), Ontario and Rouyn-Noranda (RN), QuÈbec Canada) in two seasons (spring and summer). The objectives of this study were (i) to examine the influences of aqueous and dietary metal contamination on yellow perch liver and kidney metal accumulation; (ii) to compare the seasonal and regional variations in gut content and tissue metal concentrations along the two gradients studied; and (iii) to investigate the potential of metals for tissue accumulation under conditions of life-long chronic exposure. Contaminated RN lakes were characterized by elevated concentrations of Cd, Cu and Zn in water and sediment, while contaminated Sudbury lakes were characterized by elevated concentrations of Cd, Cu and Ni in water, and Cu and Ni in sediment. Dietary metal contamination largely reflected water and sediment contamination for Cd and Cu and to a lesser extent for Ni and Zn, but not for Se. Liver and kidney concentrations of Cd and Cu, and to a lesser extent Ni, Se and Zn, also correlated with dietary contamination, indicating that both aqueous and dietary sources are significant contributors for these metals. Dietary metal concentrations often decreased, but never increased, with size, suggesting that metal exposure through diet generally decreases in larger yellow perch. Although Cd accumulated in the tissues of older fish from some lakes in the RN region, overall, metals did not accumulate with age in liver or kidney of fish from either region. Seasonal variations in tissue metal concentrations were inconsistent between regions, and sometimes also between tissues. Our data suggests that S fish, having been historically exposed to high concentrations of Cu and Ni, may have evolved better capacities for the regulation of tissue concentrations of these metals compared to RN fish. Finally, of all the metals examined, Zn appeared to be the most regulated, and Cd the least. This data clearly highlights the importance of repeated sampling for assessing effects of metal contaminants in wild fish, and further suggests that yellow perch from Sudbury may have adapted to metal exposure.

Branchial binding kinetics and gastro-intestinal uptake of copper and cadmium where examined in yellow perch (Perca flavescens) from a metal-contaminated lake (Hannah Lake, Sudbury, Ontario, Canada) and an uncontaminated lake (James Lake, North Bay, Ontario, Canada). An in vivo approach was taken for gill binding comparisons while an in vitro gut binding assay was employed for gastro-intestinal tract (GIT) uptake analysis. By investigating metal uptake at the gill and the gut we cover the two main routes of metal entry into fish. Comparisons of water and sediment chemistries, metal burdens in benthic invertebrate, and metal burdens in the livers of perch from the two study lakes clearly show that yellow perch from Hannah L. are chronically exposed to a highly metal-contaminated environment compared to a reference lake. We found that metal-contaminated yellow perch showed no significant difference in gill Cd binding compared to reference fish, but they did show significant decreases in new Cd binding and absorption in their GITs. The results show that gill Cd binding may involve low-capacity, high-affinity binding sites, while gastro-intestinal Cd uptake involves binding sites that are high-capacity, low-affinity. From this we infer that Cd may be more critically controlled at the gut rather than gills. Significant differences in branchial Cu binding (increased binding) were observed in metal-contaminated yellow perch. We suggest that chronic waterborne exposure to Cu (and/or other metals) may be the dominant influence in gill Cu binding rather than chronic exposure to high Cu diets. We give supporting evidence that Cd is taken up in the GIT, at least in part, by a similar pathway as Ca(2+), principally that elevated dietary Ca(2+) reduces Cd binding and uptake. Overall our study reveals that metal pre-exposure via water and diet can alter uptake kinetics of Cu and Cd at the gill and/or the gut.

Zinc is an essential micronutrient for freshwater fish but can be toxic to them at elevated concentrations. Therefore, the regulation of zinc uptake is important in maintaining homeostasis when fish are chronically exposed to elevated zinc in nature. This study examined the kinetics of in vivo branchial and in vitro intestinal zinc uptake in wild yellow perch (Perca flavescens) from metal-contaminated and reference lakes in northern Ontario. The results showed that the branchial zinc uptake involves high affinity transport sites whereas the intestinal zinc uptake involves low affinity transport sites. Interestingly, significant alterations in the branchial zinc uptake (reduced affinity, increased maximum transport rate) but no apparent changes in the intestinal zinc uptake characteristics were observed in the metal-impacted yellow perch population relative to the reference population. Subsequently, no differences in zinc concentrations of gill, liver and whole body were recorded between reference and metal-impacted yellow perch populations. Overall, our study indicated that the gill, not the gut, likely plays a critical role in maintaining the zinc homeostasis in wild fish under chronic exposure.

DOI: 10.1080/10807030701340995 Gregory G. Pyle a & Reehan S. Mirzaa pages 492-505. Available online: 11 May 2007. ...

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Fish rely on chemosensation to alert them of nearby predators. Recent evidence suggests that metals disrupt this chemical communication system. Our objective was to determine the chemical alarm response of juvenile fathead minnows after embryonic copper (Cu) exposure. Embryos were randomly assigned to one of two treatments: clean water or water containing 10 [mu]g/L Cu. Once hatched, half of the Cu-exposed embryos were transferred to clean water (after hatch), while the other half remained in the Cu-contaminated water. Fish were tested using a triumvirate maze at the age of 84-96 d post-hatch. Fish reared in clean water significantly avoided the alarm cue. However, fish reared under continuous Cu exposure and those that were only exposed to Cu during embryonic development were unable to respond to the chemical alarm stimulus. Fish from all treatments did not respond to two control stimuli. Results from this study suggest that fish exposed to elevated Cu concentrations during embryonic development is sufficient to impair chemosensory function during later life stages. This could result in an inability to detect nearby predators by olfaction, which could lead to important ecological perturbations in populations inhabiting metal-contaminated systems.

The purpose of this study was to examine relationships among water, sediment, and fish tissue metal concentrations as they relate to fish diversity, tissue metal accumulation, and fish morphometric and reproductive condition. Fish were captured in 12 lakes near Sudbury, Ontario, Canada, that ranged in their degree of metal contamination. In general, metal concentrations in water and sediment decreased with increasing distance from industrial operations. However, only Cu and Ni demonstrated this trend in sediments. Although 20 fish species were identified in the 12 lakes, only one species, yellow perch (Perca flavescens), was common to all 12 lakes. Fish diversity was only associated with sediment metals, suggesting that short-term processes are much less important than long-term processes for fish community recovery in metal-contaminated lakes. Multivariate characterization of water metal concentrations resulted in three lake clusters: Group 1 consisted of reference lakes; Group 2 lakes had high alkalinity, conductivity, hardness, pH, waterborne metals (especially Se), and sediment Cu and Ni concentrations; Group 3 lakes had high pH, waterborne and sediment Cu, and sediment Ni, intermediate alkalinity, conductivity, and waterborne metals (except Al and Fe), and low hardness and waterborne Al and Fe. Liver Cd, Cu, Ni, Pb, and Zn, muscle Zn, and intestinal Cd and Zn were highest, and muscle Cu and male gonadosomatic index (GSI) were lowest, in Group 3 fish. Liver, muscle, and intestinal Se concentrations, and Fulton's condition factor (FCF), hepatosomatic index (HSI), and male GSI were highest in Group 2 fish. Group 1 fish had the highest muscle Hg concentrations and female GSI. Muscle Se appeared to have an antagonistic effect on muscle Hg accumulation as a function of distance from smelting operations. Neither Cu nor Ni, both metals of concern in the Sudbury area, was useful for predicting fish condition, probably because of homeostatic regulatory control. Liver Cd accumulation, which was negatively related to FCF (r=-0.16; P), exhibited strong, nonlinear inhibition (r2=0.99; P) as a function of water hardness. Because Cd was not detected in water samples in this study, we suspect that branchial Ca2+ uptake may play some role in reducing dietary Cd uptake in hard water lakes. Selenium has received relatively little attention in the contaminated systems around Sudbury, yet our results demonstrated that tissue Se was related to all condition metrics studied. Moreover, evidence was provided that suggests that there is a gender-specific interaction between dietary Se and Cu uptake that may contribute to decreased female reproductive condition in wild yellow perch.

This study evaluated the >400-fold tolerance to acute waterborne Cd of a metal-tolerant fish, yellow perch (YP, Perca flavescens), relative to a sensitive model fish, rainbow trout (RBT, Oncorhynchus mykiss), from the perspective of the acute Cd biotic ligand model (BLM). Three-hour gill binding characteristics for Cd and its competitor, Ca, in both species exhibited only small quantitative differences, but gill Cd accumulations at 3 h and 24 h, which were associated with 50% lethality at 96 h (3- and 24-h LA50s), were 52- to 60-fold higher in YP relative to RBT. However, the acute Cd BLM cannot be extended from RBT to YP by simple adjustments of LA50 values because unlike RBT, in YP, LA50s (3 and 24 h) were 26- to 47-fold greater than the capacity of the characterized set of Cd-binding sites. Moreover, 3-h gill Ca and Cd binding characteristics in wild YP, collected from one clean (Geneva) and two metalcontaminated softwater lakes (Hannah and Whitson) around Sudbury region, northern Ontario, revealed that chronic waterborne factors like hardness and Cd preexposure can influence both Cd and Ca binding in fish gills and could have major implications for the future refinement of the acute Cd BLM approach.

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doi: 10.1139/Z04-034 © 2004 NRC Canada 694 Received 26 August 2003. Accepted 2 March2004. Published on the NRC Research Press Web site at http://cjz.nrc.ca http://cjz.nrc.ca on 22 June 2004. TDMcPherson and GG Pyle.1 Department of Biology, Nipissing University, PO Box 5002 ...

The objective of this study was to evaluate the effects of copper exposure on swimming performance and gill-binding characteristics of wild yellow perch (Perca flavescens), a species endemic to metal-contaminated lakes of the Sudbury region in northern Ontario. Yellow perch were collected from lakes varying in the degree of metal contamination (Cu = 1-21 microg/l), on two separate occasions for the investigation of swim performance and the analysis of gill-binding characteristics. Swim performance tests indicated that yellow perch from the contaminated lake had slightly greater endurance in a fixed velocity sprint test than fish from reference lakes, although the analysis of critical swimming speeds (U(crit)) did not reveal this same distinction between the groups. Differential sprint performance was in part due to differences in fish size within contaminated and reference lakes. Yellow perch from the contaminated lake also had higher resting levels of muscle glycogen and greater lactate production during high intensity exercise compared to yellow perch from the reference site. Acclimation occurred in the metal-contaminated yellow perch, as seen by the significantly elevated time to death (LT50) during an acutely lethal challenge to 600 microg Cu/l. However, gills from perch from the contaminated lake accumulated about three times more copper at death. In contrast, at a lower exposure range of water-copper (10-400 microg/l), the gills of fish from the contaminated lake tended to saturate with copper at lower concentrations than gills of fish from the reference lake (approximately 8 microg versus 23 microg Cu/g of gill tissue). In addition, perch from the contaminated lake exhibited a lower rate of sodium loss during the acute exposure to copper at approximately 10 to 600 microg Cu/l. This study suggests that the amount of copper bound to (or accumulated within) the gills may not be diagnostic of acute toxicity for wild yellow perch from metal-contaminated lakes.

Ours is the first study to demonstrate an influence of dietary sodium on waterborne copper uptake in fish. We examined possible interactions between dietary sodium and the response of freshwater rainbow trout (Oncorhynchus mykiss) to waterborne copper in light of recent evidence of interactions between sodium and copper metabolism in the gills. Trout were maintained for 6 days on one of four diets of increasing sodium concentration (0.25 mmol g(-1), 0.51 mmol g(-1), 0.76 mmol g(-1) and 1.27 mmol g(-1), which corresponds to 0.6%, 1.2%, 1.8% and 3% sodium by mass, respectively). At the end of 7 days, fish were exposed for 6 h to waterborne copper spiked with (64)Cu to determine if the dietary sodium affected responses to a subsequent short-term waterborne copper exposure. The radiotracer allowed us to distinguish between Cu occurring in fish tissues before the experiment and 'newly accumulated' Cu arising from the experimental exposure. Dietary sodium concentrations of 1.8% or 3% reduced newly accumulated copper concentrations in gill (from 93.9 ng g(-1) in control to 38.9 ng g(-1) and 20.0 ng g(-1) in fish fed 1.8% or 3% Na(+)-supplemented diets, respectively), liver (from 64.3 ng g(-1) to 23.1 ng g(-1) and 7.5 ng g(-1), respectively), kidney (from 29.3 ng g(-1) to 11.7 ng g(-1) and 7.8 ng g(-1), respectively), plasma (from 64.7 ng g(-1) to 21.5 ng g(-1) and 10.7 ng g(-1), respectively) and gut (from 6.8 ng g(-1) to 3.4 ng g(-1) and 2.2 ng g(-1), respectively) by 50.0-88.2%. The 3% Na(+)-supplemented diets also increased plasma and gut sodium concentrations by 38.1% (from 137.1 micromol g(-1) to 189.3 micromol g(-1)) and 104.3% (from 56.5 micromol g(-1) to 115.4 micromol g(-1)), respectively, relative to fish maintained on untreated diets. Whole body uptake rates of both sodium and copper were significantly reduced, and highly correlated (r=0.97) with one another, in fish fed high-sodium diets relative to controls. Moreover, sodium efflux was 12% and 38% higher in fish fed 1.8% and 3% sodium-enriched diets, respectively. Fish fed high-sodium diets also drank more water, but the contribution of drinking to waterborne copper uptake was negligible. From these results, we speculate that, at least in part, aqueous sodium and copper share a common branchial uptake route, probably through an apical sodium channel. According to this hypothesis, as the channel is downregulated with increasing internal sodium concentrations, both sodium and copper uptake from the water are inhibited.

Juvenile rainbow trout were fed diets containing control (0.26 mmol/g) or elevated (1.3 mmol/g) dietary Na1 in combination with either background (19 nmol/L) or moderately elevated levels (55 or 118 nmol/L) of waterborne Cu for 21 d. Unidirectional waterborne Na1 uptake rates (measured with 22Na) were up to four orders of magnitude higher than those of Cu (measured with 64Cu). Chronic exposure to elevated dietary Na1 alone or in combination with elevated waterborne Cu decreased whole-body uptake rates of waterborne Na1 and Cu. Accumulation of new Cu and Na1 at the gills was positively and highly significantly correlated and responded to the experimental treatments in a similar fashion, suggesting that Na1 and Cu have common branchial uptake pathways and that dietary Na1 preexposure modifies these pathways. Chronic exposure to elevated waterborne Cu significantly increased Cu concentrations in the liver but caused only modest increases in total Cu concentrations in the whole body and gill. Chronic exposure to elevated dietary Na1 slightly decreased whole-body Cu concentration on day 14 and greatly reduced liver Cu concentration on days 14 and 21; new Cu accumulation in whole-body, gill, and internal organs was reduced on all days. Chronic exposure to elevated waterborne Cu or dietary Na1 alone reduced short-term gill Cu binding at low waterborne Cu concentrations. At high waterborne Cu concentrations, chronic exposure to elevated waterborne Cu had no effect, while elevated dietary Na1 increased Cu binding to the gills. Combined chronic exposure to elevated dietary Na1 and waterborne Cu decreased gill Cu binding over the entire range of Cu concentrations tested. Clearly, chronic exposure to elevated dietary Na1 and waterborne Cu appears to modify gill Cu-binding characteristics and may be important considerations in future development of a chronic biotic ligand model for Cu.

Nickel (Ni) is an ubiquitous, naturally occurring metal that is associated with metal mining and other industrial activities. Despite elevated Ni concentrations reported for many industrial receiving waters, Ni receives little research attention addressing factors influencing its toxicity to freshwater fish. This study examined the influence of water hardness, pH, and total suspended solids (TSS) in soft, reconstituted water on Ni toxicity to larval fathead minnows (Pimephales promelas). Increasing water hardness from 20 to 140 mg/L (as CaCO3) reduced acute Ni toxicity by 5-fold (96-h LC50s 0.45 and 2.27 mg Ni/L, respectively). Low pH had a slight protective effect against Ni toxicity relative to neutral pH conditions. At pH 5.5, the 96-h LC50 was 0.69 mg Ni/L, compared to 0.54 mg Ni/L at pH 7.0. However, Ni toxicity was significantly reduced at pH 8.5 where the 96-h LC50 was 2.21 mg Ni/L. These results were explained on the basis of Ni speciation. Total suspended solids also reduced Ni toxicity (expressed as 96-h LC50s) from 0.35 to 1.12 mg Ni/L over a TSS range of 10 to 100 mg/L. This reduction of toxicity due to TSS is significant because mine effluents often have a combination of elevated TSS and metals. The ameliorative effect of TSS was not as significant as high hardness or pH probably because there is a TSS threshold, after which physical irritation to fish gills counteracts any protective effect conferred by TSS. This finding is relevant to choices made in design of mine effluent treatment systems; i.e., there may be an optimum range of TSS concentrations that protect aquatic biota against effects of metals that remain after treatment.

Elevated concentrations of arsenic, nickel, and molybdenum in aquatic systems around northern Saskatchewan uranium mines are an environmental concern. Early life stage fathead minnows were used to assess toxicity from several aquatic systems near the Key Lake and Rabbit Lake uranium operations. Hatching success of fish embryos exposed to waters receiving contaminants associated with uranium ore milling was reduced by 32-61% relative to controls. Mortality differed in two lakes receiving mill effluents because of opposing factors influencing metal toxicity (i.e. low pH and high hardness). In one mill receiving water (Fox Lake), larval mortality was 0%, whereas mortality was 85% in water collected from a downstream location (Unknown Lake). Fish embryos exposed to open-pit dewatering effluent receiving waters, or water from a flooded open pit (i.e. pit waters), hatched 26-39% earlier than those exposed to reference or control water. The combination of low water hardness and elevated nickel concentrations in pit waters contributed to the early hatching. Egg hatchability and hatching time were more sensitive indicators of toxicity than 'standard' endpoints, like larval mortality and growth. Current regulatory emphasis on single contaminants and standard toxicological endpoints should be re- evaluated in light of the complex interaction among confounding variables such as pH, hardness. conductivity, and multi-metal mixtures.

The effects of chronic exposure to waterborne Cd and elevated dietary Ca, alone and in combination, were examined in juvenile rainbow trout, Oncorhynchus mykiss. Fish were chronically exposed to 0.05 (control) or 2.56 microg/l Cd [as Cd(NO3)2*4H2O] and were fed 2% body mass/day of control (29.6 mg Ca/g) or Ca-supplemented trout food (52.8 mg Ca/g as CaCl2*2H2O). Cd accumulated mainly in gill, liver, and kidney. Waterborne Cd inhibited unidirectional Ca uptake from water into the gill and induced hypocalcemia in the plasma on day 40. Waterborne Cd also induced an elevated Ca concentration on day 20 in the gill tissue of trout fed the Ca-supplemented diet and a decreased Ca concentration on day 35 in the gills of trout fed the control diet. Dietary Ca protected against Cd accumulation in gill, liver, and kidney, but did not protect against the inhibition of Ca uptake into the gill or plasma hypocalcemia. When fed Ca-supplemented diet and exposed to waterborne Cd, fish showed 35% mortality, compared to 0-2% in control fish and in the Cd-exposed fish with normal Ca in the diet. Growth, on the other hand, was not affected by any treatment.

Larval fathead minnows (Pimephales promelas) were placed at four exposure sites for 7 days in each of five lakes surrounding the Key Lake uranium mine in northern Saskatchewan, Canada. Fish placed in lakes receiving Mo-contaminated mill effluent demonstrated higher mortalities than those placed in lakes receiving Ni-contaminated mine-dewatering effluent, which was not significantly different from reference sites. No significant differences were detected in fish growth among the study lakes because of the high (90%) mortality in Fox and Unknown lakes. Principal components analysis characterized exposure sites by total- and dissolved-metal concentration. Stepwise multiple regression of fish mortality on principal components (PCs) generated from total-metal data showed that PC1 could account for 84% of the variance associated with fish mortality. Careful examination of the metals that correlated strongly with PC1 and with fish mortality suggested that dietary Se toxicity probably resulted in the differential fathead minnow mortality observed among study lakes.

Equilibrium conditions are often assumed in dose and risk calculations based on the simple linear concentration factor model, a commonly used model in the study of contaminant flow through ecosystems. It has been argued that by using a power function model to describe radionuclide retention in fish, equilibrium may never be achieved under natural conditions, thereby violating the equilibrium requirement in the concentration factor model. Our results demonstrate uranium-series radionuclide equilibria in a natural population of common white sucker (Catostomus commersoni). Concentration factors indicated that 226Ra, 232Th, 230 Th, and 228Th preferentially deposited in bone over muscle. Although 226Ra had the highest concentration in bone, 228Th yielded the highest concentration factors for water-to-bone transfer. 232Th may not be in equilibrium because of a growth dilution effect.

Uptake of 226Ra, 232Th , 23OTh, and 228Th from water, sediment, and diet sources to bone and muscle of white suckers (Catostomus commersoni) was studied in sixteen lakes in the uranium-mining district of Ontario, Canada. Fish tissues did not increase linearly with environmental concentrations. The best relationship appears to be a power function. This has implications for the accuracy of radiological dose and risk estimates for uranium mining impacts, which are often based on a linear model.

Equilibrium conditions are assumed in the simple linear concentration factor model commonly used in simulations of contaminant flow through ecosystems and in dose and risk calculations. Predictions derived from a power function model have suggested that if the time scale of the food-chain transfer is less than six years in fish, radium226 equilibrium will not be achieved in nature, thereby violating the equilibrium requirement in the concentration factor model. Our results indicate "Ra equilibrium is achieved in a natural population of lake herring (Coregonus artedii), contrary to predictions of the power function model.