Cadmium affects the social behaviour of rainbow trout,Oncorhynchus mykiss

The present study investigated both the effects of cadmium on the social interactions of rainbow trout and the differential accumulation of waterborne cadmium among social ranks of fish. Fish exposed to waterborne cadmium concentrations of 2 microg l(-1) for 24 h, followed by a 1, 2 or 3 day depuration period in clean water, had a decreased ability to compete with non-exposed fish. However, the competitive ability of exposed fish given a 5 day depuration period was not significantly impaired. Cadmium accumulated in the olfactory apparatus of fish exposed to waterborne cadmium for 24 h and decreased significantly only after 5 days depuration in clean water. Among groups of ten fish held in stream tanks, where all fish were exposed to cadmium, there were significant effects on social behaviour and growth rate. Dominance hierarchies formed faster among fish exposed to cadmium than among control fish, and overall growth rates were higher in the cadmium treatment. In groups of ten fish, social status also affected tissue accumulation of cadmium during waterborne exposure, with dominant fish accumulating more cadmium at the gill. In conclusion, exposure to low levels of cadmium, affects the social behaviour of fish, in part due to accumulation in the olfactory apparatus, and dominant fish accumulate more gill cadmium than subordinates during chronic waterborne exposure.     

Trophic transfer and dietary toxicity of Cd from the oligochaete to the rainbow trout

Dietary toxicity of metals on fish is often studied using commercial pellet food, and there is a lack of investigation on the toxicity of metals that are biologically incorporated into the natural food from the aquatic environment. In this study, we investigated the toxicity of dietborne Cd from the oligochaete Lumbriculus variegatus to the rainbow trout Oncorhynchus mykiss. The oligochaete worms were exposed to waterborne Cd (0.1, 5, 20, and 200 microgL(-1)) for 1 week and the fish were fed this food exclusively (daily ration=3.5% body wet weight) for 1 month. Cd concentrations in the worms averaged 0.1, 0.6, 2.2, and 30.3 microgg(-1) wet weight respectively, whereas the whole fish accumulated 0.002, 0.005, 0.019, and 0.387 microg Cd g(-1) wet weight respectively, after feeding upon control or Cd-contaminated worms for 4 weeks. Highest concentrations of Cd were retained in the gut, followed by the kidney and liver of the fish, with the latter two increasing over time; however, gut tissue accounted for >80% of whole body Cd burdens at all times. The trophic transfer efficiency of Cd was low (0.9-6.4%) although higher than in previous studies using Cd-spiked commercial diets, and was only weakly correlated to the internal Cd storage in the worms. The level of Cd in the contaminated worms did not affect Cd trophic transfer efficiency, but was reduced over the dietary exposure period. Dietborne Cd did not interfere with whole body Ca uptake from the water or alter plasma [Ca], but reduced growth by 50% in the trout exposed to the highest Cd dose. Cd stored in the metallothionein-like proteins of the fish gut tissue increased while that in the heat-denaturable proteins was reduced, suggesting detoxification over time. This study suggests a higher bioavailability and toxicity of Cd from the natural diets than from the commercial diets used in previous studies.     

Physiological effects of copper in the euryhaline copepod Acartia tonsa: waterborne versus waterborne plus dietborne exposure

The physiological effects of waterborne and waterborne plus dietborne copper exposure were determined in the euryhaline copepod Acartia tonsa at different salinities (5, 15 and 30ppt). Copepods were exposed (48h) to a reported 48-h LC50 for copper (CuCl(2)), which had been previously determined under the same experimental conditions. Whole body copper accumulation, ion concentrations (Na(+), Cl(-), Mg(2+)), and Na(+), K(+)-ATPase activity were the endpoints measured in all experimental groups. Feeding rate was also measured in fed experimental groups. In copper-exposed copepods, whole body copper accumulation was dependent on salinity, decreasing as salinity increased. However, it was similar in copepods exposed to waterborne and waterborne plus dietborne copper, irrespective the salinity tested. Waterborne copper exposure induced a disturbance of the whole body Na(+) concentration in all salinities tested. This effect was characterized by an increased whole body Na(+) concentration in seawater (salinity 30ppt) and a decreased whole body Na(+) concentration at lower salinities (5 and 15ppt). The ionoregulatory imbalance in low salinity (5ppt) was associated with an inhibition of the whole body Na(+), K(+)-ATPase activity, as observed in freshwater fish and crustaceans. When copepods were exposed to waterborne plus dietborne copper, the physiological effects described were only observed at a low salinity (5ppt) and were associated with a marked inhibition of the feeding rate. Taken altogether, the data suggest that the physiological effects induced by waterborne copper exposure in A. tonsa acclimated to higher salinities (15 and 30ppt) are due to a combined effect of food restriction and copper exposure. Differential physiological responses to waterborne and waterborne plus dietborne copper cannot be ascribed to differences in whole body copper burden.     

Preliminary investigations on the comparative chronic toxicity of four dietary arsenicals to juvenile rainbow trout (Salmo gairdneri R.)

Juvenile rainbow trout were fed semi-purified diets in eight-week growth trials to compare the toxicity of four dietary arsenicals: arsenic trioxide (AT); disodium arsenate heptahydrate (DSA); dimethylarsinic acid (DMA); and arsanilic acid (AA). Toxicity responses of reduced growth and feed consumption, and altered feeding behaviour, were noted at all levels of supplementation of AT and DSA (137–1477 μg As/g diet). In contrast, even at the highest levels of supplementation (1497 μg As/g diet as DMA, and 1503 μg As/g diet as AA) the organic arsenicals did not result in these toxicity signs.Carcass arsenic concentration showed a dose-response relationship to dietary arsenic concentration and exposure rate, for each of the arsenicals investigated. At lower levels of exposure, dietary DSA yielded the highest carcass arsenic concentrations, while at higher levels, dietary AT yielded the highest residues.The ‘no observed effect concentration’ (NOEC) for dietary arsenic lies between 1 and 137 μg As/g diet for DSA, between 1 and 180 μg As/g diet for AT, and is at least 1497 μg As/g diet for DMA and AA. It was concluded that disodium arsenate was the most toxic to juvenile rainbow trout of the four dietary arsenicals studied.     

Effects of chronic copper exposure on the nutritional composition of Hyalella azteca

The toxicity of dietborne metals currently is a topic of high interest in aquatic toxicology. We hypothesized that, in addition to causing direct physiological effects when ingested by organisms, dietborne metals might also cause indirect foodweb effects. One such indirect effect might be alteration of the nutritional content of prey, leading to decreased growth and (or) survival of consumers. Because dietborne and waterborne metal exposures usually occur concurrently in aquatic ecosystems, we exposed two generations of a representative grazer species-the freshwater amphipod Hyalella azteca-to dietborne copper (Cu) concurrent with waterborne Cu in the laboratory for a total of 27 days (first generation) and 45-57 days (second generation). The aqueous Cu concentrations were 0.0099 (control), 0.054 and 0.11 microM (0.6, 3.4 and 7.0 microg Cu per l, respectively) at 24 degrees C, pH 7.5-8.3, alkalinity of approximately 3 mEq/l and hardness of approximately 4 mEq/l; whereas the dietborne Cu exposures were via biofilm growing on cotton gauze in the same exposure aquaria. In a preliminary test, we demonstrated that the highest Cu concentrations were at the threshold for adversely affecting survival and reproduction. In the two-generation test, first- and second-generation amphipods exposed to the intermediate and high aqueous Cu concentrations accumulated significantly higher amounts of Cu than control amphipods. However, none of the traditional nutritional composition categories (protein, total lipid, ash and 'other') differed among the treatments. The only significant difference in nutritional composition was an elevated concentration of linolenic acid (18:3 n-3) in the second-generation amphipods exposed to 0.054 microM Cu.     

The physiological effects of a biologically incorporated silver diet on rainbow trout (Oncorhynchus mykiss)

Silver was biologically incorporated into a diet by exposing rainbow trout for 7 days to 100 mg/l of waterborne silver as silver thiosulphate. These fish were processed into a fine powder (trout meal) and pelleted to form a nutritionally balanced feed which was then fed to juvenile rainbow trout (Oncorhynchus mykiss). Fish were fed either a diet containing 3.1 microg/g biologically incorporated silver (an environmentally relevant concentration), or one of three control diets containing approximately 0.05 microg/g Ag for 128 days. All dietary treatments were fed to satiation once daily. Dietary silver did not significantly affect mortality, growth, food consumption, or food conversion efficiency. Furthermore, ion regulation (plasma Na(+) levels and Na(+) influx rates), hematological parameters (hematocrit, plasma protein, hemoglobin levels), plasma glucose, metabolism (oxygen consumption, ammonia and urea excretion rates) and intestinal Na/K-ATPase and amylase activities were all unaffected. Based on the physiological parameters investigated here, this dietary silver exposure appeared to be physiologically benign to rainbow trout. However, silver concentrations in the livers of the silver-fed fish were significantly elevated at day 16, and reached a steady-state level of approximately 20 microg/g Ag by day 36. The concentration specific accumulation rate in the livers of fish fed biologically incorporated silver was about 4.6 orders of magnitude greater than when fed dietary silver sulfide, indicating much greater bioavailability. Despite this increase, hepatic metallothionein concentrations remained unchanged, in contrast to waterborne exposures, indicating that bioaccumulated silver behaves differently depending on whether it is taken up from the diet or from the water. Apart from a significant reduction in hepatic Cu at day 16, liver concentrations of Cu and Zn were not affected by dietary silver. Silver concentrations were also significantly elevated (relative to control fish) in the kidneys of the silver-treated fish on days 88 and 126, and in the gills and plasma at day 126.     

A physiologically based toxicokinetic model for the uptake and disposition of waterborne organic chemicals in fish

A physiologically based toxicokinetic model was developed to predict the uptake and disposition of waterborne organic chemicals in fish. The model consists of a set of mass-balance differential equations which describe the time course of chemical concentration within each of five tissue compartments: liver, kidney, fat, and richly perfused and poorly perfused tissue. Model compartmentalization and blood perfusion relationships were designed to reflect the physiology of fishes. Chemical uptake and elimination at the gills were modeled as countercurrent exchange processes, limited by the chemical capacity of blood and water flows. The model was evaluated by exposing rainbow trout (Oncorhynchus mykiss) to pentachloroethane (PCE) in water in fish respirometer-metabolism chambers. Exposure to 1500, 150, or 15 micrograms PCE/liter for 48 hr resulted in corresponding changes in the magnitude of blood concentrations without any change in uptake kinetics. The extraction efficiency for the chemical from water decreased throughout each exposure, declining from 65 to 20% in 48 hr. Extraction efficiency was close to 0% in fish exposed to PCE to near steady state (264 hr), suggesting that very little PCE was eliminated by metabolism or other extrabranchial routes. Parameterized for trout with physiological information from the literature and chemical partitioning estimates obtained in vitro, the model accurately predicted the accumulation of PCE in blood and tissues, and its extraction from inspired water. These results demonstrate the potential utility of this model for use in aquatic toxicology and environmental risk assessment.     

Effects of chronic sublethal exposure to waterborne Cu, Cd or Zn in rainbow trout. 1: Iono-regulatory disturbance and metabolic costs

The relationships among growth, feeding behaviour, ion regulation, swimming performance and oxygen consumption in rainbow trout (Oncorhynchus mykiss) were compared during chronic exposure (up to 100 days) to sublethal levels of waterborne Cd (3 μg.l(-1)), Cu (75 μg.l(-1)) or Zn (250 μg.l(-1)) in moderately hard water (hardness of 140 mg.l(-1), pH 8). A pattern of disturbance, recovery and stabilization was evident for all three metal exposures, although the degree of disturbance, specific response and time course of events varied. Growth was unaffected by any of the metals under a regime of satiation feeding but appetite was increased and decreased in Cu- and Cd-exposed trout respectively. Critical swimming speed was significantly lowered in fish chronically exposed to Cu, an effect associated with elevated O(2) consumption rate at higher swimming speeds. Branchial Na(+)/K(+) ATPase activity was elevated in Cu-exposed fish but not in Cd-exposed trout. Disruption of carcass Na(+) and Ca(2+) balance was evident within 2 days of exposure to either Cd, Cu or Zn, with subsequent recovery to control levels. The loss of Ca(2+) in trout exposed to waterborne Cd persisted longest, and recovery took approximately a month. The physiological response of trout to chronic Cu exposure involves mechanisms that result in an associated metabolic cost. In comparison, Cd is neither a loading nor a limiting stress and acclimation to chronic Cd-exposure does not appear to involve a long term metabolic cost.     

The influence of ration size on copper homeostasis during sublethal dietary copper exposure in juvenile rainbow trout,Oncorhynchus mykiss

The influence of ration size on homeostasis and sublethal toxicity of copper (Cu) was assessed in rainbow trout (Oncorhynchus mykiss) during dietary Cu exposure in synthetic soft water. A constant dietary dose of 0.24 micromol Cu per g fish per day as CuSO(4).5H(2)O was delivered via diets containing 15.75, 7.87, and 5.24 micromol Cu g(-1) fed at 1.5, 3.0, and 4.5% wet body weight daily ration, respectively. Juvenile rainbow trout showed clear effects of ration but not Cu on growth suggesting that growth is hardly a sensitive endpoint for detection of sublethal dietary Cu exposure. All Cu-exposed fish accumulated the same total metal load when expressed on a per fish basis. This suggests that differences in tissue and whole-body Cu concentrations among the treatments reflected the differences in the fish size rather than total Cu accumulation, and demonstrate that absorption and accumulation of Cu from the gut during dietary exposure are independent of the food quantity in which the Cu is delivered. Fish fed a high ration exhibited greater mass-specific unidirectional uptake of waterborne Cu than fish fed a low ration indicating an increased need for Cu for growth processes in rapidly growing fish. Stimulated excretion of Cu was indicated by greater Cu accumulation in the bile of the Cu-exposed fish. Branchial Na(+), K(+)-ATPase was not affected by dietary Cu exposure or ration but gut Na(+), K(+)-ATPase activities showed stimulatory effects of increasing ration but not of Cu exposure. The 96-h LC50 for waterborne Cu (range 0.17-0.21 micromol l(-1) (10.52-13.20 microg l(-1)) was the same in all treatment groups indicating that ration size was unimportant and that dietary Cu did not induce an increase in tolerance to waterborne Cu. Taken together these results suggest that the nutritional status, fish size, and growth rates should be considered when comparing whole-body and tissue Cu concentration data for biomonitoring and risk assessment. Moreover, expressing the exposure as total metal dose rather than metal concentration in the diet is more appropriate.     

Influence of acclimation and cross-acclimation of metals on acute Cd toxicity and Cd uptake and distribution in rainbow trout (Oncorhynchus mykiss)

The development of chronic metal toxicity models for fresh water fish is complicated by the physiological adjustments made by the animal during exposure which results in acclimation. This study examines the influence of a pre-exposure to a chronic sublethal waterborne metal on acclimation responses as well as the uptake and distribution of new metal into juvenile rainbow trout. In one series of tests, trout were exposed to either 20 or 60 microg/L Cu, or 150 microg/L Zn for a month in moderately hard water and then cross-acclimation responses to Cd were measured in 96 h LC(50) tests. Cu exposed trout showed a cross-acclimation response but Zn exposed trout did not. Using these results, a detailed examination of Cd uptake and tissue distribution in metal-acclimated trout was done. Trout were exposed to either 75 microg/L Cu or 3 microg/L Cd for 1 month to induce acclimation and subsequently, the uptake and distribution of new Cd was assessed in both Cd- and Cu-acclimated fish using (109)Cd. The pattern of accumulation of new metal was dramatically altered in acclimated fish. For example, in 3 h gill Cd binding experiments, Cd- and Cu-acclimated trout both had a higher capacity to accumulate new Cd but only Cu-acclimated fish showed a higher affinity for Cd compared to unexposed controls. Experiments measuring Cd uptake over 72 h at 3 microgCd/L showed that the Cd uptake rate was lower for Cd-acclimated fish compared to both Cu-acclimated fish and unexposed controls. The results demonstrate the phenomenon of cross-acclimation to Cd and that chronic sublethal exposure to one metal can alter the uptake and tissue distribution of another. Understanding how acclimation influences toxicity and bioaccumulation is important in the context of risk assessment. This study illustrates that knowledge of previous exposure conditions is essential, not only for the metal of concern, but also for other metals as well.     

Dietary accumulation and biochemical responses of juvenile rainbow trout (Oncorhynchus mykiss) to 3,3',4,4',5-pentachlorobiphenyl (PCB 126)

Juvenile rainbow trout (Oncorhynchus mykiss) (initial weights 2-5 g) were exposed to three dietary concentrations (0, 12.4 and 126 ng g(-1), wet weight) of a 14C-labelled 3,3',4,4',5-pentachlorobiphenyl (PCB 126) for 30 days followed by 160 days of clean food. We assessed bioaccumulation, histology (liver and thyroid) and biochemical responses (liver ethoxyresorufin-O-deethylase (EROD), liver vitamins (retinoids and tocopherol) and muscle thyroid hormone levels) along with growth and survival. The half-life of PCB 126 in the rainbow trout ranged from 82 to 180 days while biomagnification factors (BMF) ranged from 2.5 to 4.1 providing further evidence that PCB 126 is among the most bioaccumulative PCB congeners. Toluene extractable 14C declined with time in the trout suggesting the possibility of some biotransformation and/or covalent bonding with biological macromolecules. The threshold for liver EROD induction by PCB 126 was approximately 0.1 ng g(-1) (wet weight). EROD activities in the low- and high treatments were 9 and 44 times greater than control, respectively, and remained elevated throughout the experiment. EROD activity was correlated with whole body concentrations of PCB 126 although there was evidence of EROD activity suppression in the highly exposed fish. Liver didehydroretinoids and tocopherol concentrations were depressed by the high PCB 126 dose after 30 days exposure. Initially, muscle concentrations of thyroxine (T4) and triiodo-L-thyronine (T3) declined as the fish grew during the experiment, and exposure to PCB 126 accelerated the growth related decline. More information is needed to assess the functional significance of the reduced muscular stores of thyroid hormones. Despite the changes in liver EROD, liver vitamins and muscle thyroid hormones, liver and thyroid histology in trout examined after 30 days exposure and growth parameters were unaffected by PCB 126. This indicates that the functional competences of the physiological factors associated with growth were maintained under the experimental conditions.     

Dynamic multipathway modeling of Cd bioaccumulation in Daphnia magna using waterborne and dietborne exposures

We tested the predictive ability of the dynamic multipathway bioaccumulation model (DYMBAM) to characterize Cd accumulation in Daphnia magna, a species commonly used in toxicity tests and because of its sensitivity, particularly to metals, a species that is relied upon in ecological risk assessments. We conducted chronic exposure experiments in which D. magna were exposed to either dietborne Cd alone or to both dietborne and waterborne Cd. In the food-only treatments, the algae Chlamydomonas reinhardtii or Pseudokirchneriella subcapitata were pre-exposed to free Cd ion concentrations, [Cd(2+)], from 0.001 to 100nM (0.001-11microgL(-1)) then, on a daily feeding renewal basis, fed to D. magna over 21 days. In the water plus food treatment, D. magna were exposed for 21 days to the same range of [Cd(2+)] and fed with the same algal species that had been exposed to Cd at various concentrations. In the algal exposure media, Cd concentrations in algae were directly related to those in water and were characterized by a linear regression model using the log transformed concentration of the WHAM predicted Cd(2+) concentration. The DYMBAM was used with estimated values of the model constants for ingestion rate (0.08-0.34gg(-1)day(-1)) and growth rate (0.085-0.131day(-1)) based on our experimental data and with literature values for rate constants of Cd influx and efflux as well as Cd assimilation efficiency. Measured Cd concentrations in D. magna agreed with model predictions within a factor of 3. Using the model, we predict that food is an important contributor of Cd burden to D. magna, particularly at lower Cd exposure concentrations over an environmentally realistic gradient of free Cd in water. However, this cladoceran also takes up Cd from water and this exposure route becomes increasingly important at very high concentrations of free Cd (>10nM or 1.1microgL(-1)). Nevertheless, Cd produced lethal effects in D. magna that were exposed to this metal in water and diet, but exposure to Cd in food only did not result in toxic effects (as measured by survival and reproduction).     

Relationship between exposure duration,tissue residues,growth, and mortality in rainbow trout (Oncorhynchus mykiss) juveniles sub-chronically exposed to copper

We conducted a 56-day sub-chronic test on the effects of Cu on rainbow trout (Oncorhynchus mykiss) fry at a nominal water hardness of 100 mg l(-1) (as CaCO(3)). Response measures were growth, whole body Cu concentrations, and mortality. Significant mortality was observed in fish exposed to 54.1 microg Cu l(-1) (47.8%) and 35.7 microg Cu l(-1) (11.7%). Growth was dose-dependent over the range of Cu treatments (0-54 microg Cu l(-1)), and was modeled as a function of Cu exposure concentration and exposure duration. Calculated inhibition concentrations (based on change in wet weight through a 56-day Cu exposure) were IC(50)=54.0 microg Cu l(-1), IC(20)=21.6 microg Cu l(-1), IC(10)=10.8 microg Cu l(-1), and IC(01)=1.1 microg Cu l(-1). Measured whole body Cu was also dose-dependent, and growth of trout fry was readily modeled as a function of tissue Cu and exposure duration. This model was virtually identical to a model previously developed for rainbow trout exposed to Cu at a hardness of 25 mg l(-1). Following the 56-day exposure period, we performed a 96-h acute challenge to Cu and Cd to evaluate the effects of Cu acclimation on acute Cu and Cd toxicity. Sensitivity to Cu was dependent on the 'acclimation dose'; trout previously held in control aquaria (i.e. not acclimated to Cu) suffered over 80% mortality, whereas trout previously exposed to 35.7 microg Cu l(-1) for 56 day suffered 20% mortality. These fish also showed somewhat reduced sensitivity to Cd, suggesting acclimation to Cu can enhance tolerance to other metals. Finally, the relationship between growth response and hardness (derived from several studies) appeared to have a different slope than the hardness relationship previously observed for lethality responses.     

Estrogenicity of butylparaben in rainbow trout Oncorhynchus mykiss exposed via food and water

The estrogenic effect of butylparaben was investigated in a rainbow trout Oncorhynchus mykiss test system. Butylparaben was administered orally to sexually immature rainbow trout every second day for up to 10 days in doses between 4 and 74 mgkg(-1)2d(-1) and in the water at 35 and 201 microgl(-1) for 12 days. Plasma vitellogenin was measured before and during the exposures and the concentrations of butylparaben in liver and muscle were determined at the end of experiments. Increases in average plasma vitellogenin levels were seen at oral exposure to 9 mg butylparaben kg(-1)2d(-1). The ED50 values for increase in vitellogenin synthesis were 46, 29 and 10.5 mg butylparaben kg(-1)2d(-1), respectively, at day 3, 6 and 12. Exposure to 201 microg butylparaben l(-1) increased vitellogenin synthesis, but exposure to 35 microgl(-1) did not. Butylparaben showed little tendency to bioaccumulation in rainbow trout; less than 1 per thousand of the total amount of butylparaben administered orally at 51 mgkg(-1)2d(-1) over the 12 days experimental period was retained in liver at the end of the experiment. After 12 days exposure to 35 and 201 microg butylparaben l(-1), plasma concentrations were 9 and 183 microgl(-1), respectively, and for the fish exposed to 201 microgl(-1) there was a positive correlation between concentrations of vitellogenin and butylparaben in the plasma. On the assumption that butylparaben removed from the water phase during water exposure were taken up into the fish, butylparaben uptake rates in the fish exposed to 35 and 201 microg butylparaben l(-1) were 13 and 78 mgkg(-1)day(-1), respectively.     

Exposure to waterborne copper reveals differences in oxidative stress response in three freshwater fish species

Among species, various strategies in metal handling can occur. Moreover, the same metal concentration, or even the same metal dose, does not always seem to exert the same effect in different species. Here, we have investigated differences in a copper induced oxidative stress response between rainbow trout (Oncorhynchus mykiss), common carp (Cyprinus carpio) and gibel carp (Carassius auratus gibelio). Fish were exposed to two sub-lethal Cu concentrations, an identical concentration of 50μg/l for all fish species and an identical toxic dose which was 10% of the concentration lethal to 50% of the fish within 96h of exposure (LC50 96h value) for each of the 3 species (20μg/l for rainbow trout, 65μg/l for carp and 150μg/l for gibel carp). Different anti-oxidative enzyme (superoxide dismutase, glutathione reductase and catalase) activities and anti-oxidant (reduced glutathione and reduced ascorbate) concentrations were determined in gill samples collected after 1h, 12h, 24h, 3 days, 1 week and 1 month of Cu exposure. Changes in the measured parameters were present in all 3 species, yet a clear differentiation between fish species could be made before and during the exposure. The ascorbate levels of gibel carp were twice as high as those in common carp or rainbow trout. In contrast, the level of glutathione in rainbow trout was more than twice of that in the two other species. Also, glutathione reductase activity of rainbow trout was higher than in the other species. In rainbow trout a decrease of reduced ascorbate and reduced glutathione was observed in the beginning of the exposure, indicating that ROS scavenging molecules were under pressure. This was followed by an increase in the activity of superoxide dismutase after 3 days of exposure. In contrast, common carp and especially gibel carp enhanced their anti-oxidant enzyme activities as quickly as in the first day of exposure. Furthermore, our research seems to confirm that some fish rely more on glutathione as a first line of defence against metal exposure, while others rely more on metallothionein in combination with anti-oxidant enzymes.     

Internal redistribution of radiolabelled silver among tissues of rainbow trout (Oncorhynchus mykiss) and European eel (Anguilla anguilla): the influence of silver speciation

Influence of water Ag(I) speciation on pharmacokinetics of Ag(I) during a post-exposure period was investigated in rainbow trout (Oncorhynchus mykiss) and European eel (Anguilla anguilla). The rainbow trout is sensitive to waterborne ionic Ag(+) whereas the eel is tolerant. The fish were acclimated to either of two chloride concentrations, 10 or 1200 microM, in synthetic soft water and then exposed to a sublethal 24-h pulse of 1.3 microgl(-1) of 110mAg(I) added as 110mAgNO(3) in these waters. The protocol provided exposures to mainly the free ion Ag(+) (low chloride water) or mainly AgCl(aq) (high chloride water). Contents and concentrations of 110mAg(I) in tissues and body fluids were then monitored over a 67-day post-exposure period in Ag(I)-free water of the same chloride levels. Changing the speciation of Ag(I) in the water had no effect on the whole body load of 110mAg(I), but did result in differences in internal distribution. In trout, changing water Ag(I) speciation significantly altered elimination or accumulation of Ag(I) in several body compartments. Notably, trout exposed to AgCl(aq) eliminated 110mAg(I) from the kidney more quickly than trout exposed to Ag(I) primarily as Ag(+). This elimination was matched by higher concentrations of 110mAg in liver of trout exposed to Ag(I) primarily as AgCl(aq). In eel, shifting speciation from Ag(+) to AgCl(aq) hastened elimination of 110mAg(I) from mid and posterior intestine and increased 110mAg(I) retention in kidney. While there was no difference between the two fish species in whole body 110mAg(I) load, most internal body compartments of trout had higher 110mAg(I) concentrations than those in eel early in the experiment. Because tissue-specific elimination times were longer in eel than in trout, these differences were generally cancelled by the end of the 67-day depuration period. The only exception was the liver, which in trout continued to accumulate 110mAg(I) throughout the experiment but in eel remained unchanged. The combined effect of 110mAg(I) movements in the two species was that trout retained all their accumulated 110mAg(I) through the 67-day period, whereas the body burden of 110mAg(I) in eel was reduced to half initial values by day 67.     

Sex and low-level sampling stress modify the impacts of sewage effluent on the rainbow trout (Oncorhynchus mykiss) immune system

The objective of the present study was to investigate the influence of chronic exposure to municipal sewage treatment effluent at environmentally relevant concentrations on immune parameters in rainbow trout (Oncorhynchus mykiss), including the assessment of potential differences in reactivity between sexually mature male and female fish. Trout were exposed to 1.5 and 15% (v/v) secondary treated municipal sewage effluent for 32 weeks. Fish were injected intra-peritoneally either with inactivated Aeromonas salmonicida to simulate an infection or with PBS as control for this immune challenge 6 weeks prior to sampling. Exposure to effluent resulted in a decrease in A. salmonicida-specific serum antibody level and blood lymphocyte numbers in mature females, but not in male fish. Injection of A. salmonicida resulted in enhanced serum lysozyme activity in mature male trout, which were not exposed to effluent. This stimulating effect of A. salmonicida could not be found in effluent-exposed trout, again potentially revealing a suppressive effect of the effluent. An influence of sampling fish on two consecutive days was observed in many immune parameters, most likely reflecting handling stress. Leucocyte and lymphocyte numbers in peripheral blood were consistently lower in male and female fish on the second sampling day. Phagocytosis in head kidney macrophages from male trout was also influenced by sampling day, whereby a stimulation of this reaction occurred on the second day of sampling. Liver mixed function oxygenase activity was found to be enhanced in mature male trout exposed to 15% effluent. In conclusion, the study showed, that exposure to sewage treatment plant effluent, in surface water relevant concentrations, can lead to potentially adverse effects on selected immune reactions in rainbow trout. However, this study also demonstrated that both handling stress and the sex of mature fish have distinct influences on the immune response detected in male and female fish and are likely to influence measured immune parameters to the extent that subtle effluent induced changes may be difficult to detect.     

PCBs can diminish the influence of temperature on thyroid indices in rainbow trout (Oncorhynchus mykiss)

The influence of PCBs on the thyroid status of rainbow trout was assessed at various temperatures to identify if PCB mixtures, as well OH-PCBs produced via biotransformation of parent PCBs, can illicit thyroid effects in fish. Juvenile rainbow trout (Oncorhynchus mykiss) held at 8, 12 or 16 degrees C were exposed to dietary concentrations of an environmentally relevant mixture of PCBs for 30 days followed by a depuration phase. Two additional treatments at 12 degrees C included higher concentrations of PCBs (congeners 77, 126 and 169) known to induce CYP1A in fish (referred to as CYP1A treatment) and PCBs (congeners 87, 99, 101, 153, 180, 183 and 194) known to induce CYP2B in mammals (referred to as CYP2 treatment), to assess the influence of more biologically relevant PCB congeners on thyroid indices in fish. Growth rate and liver somatic index varied with water temperature (p<0.05) but did not differ between PCB exposed and control fish (p>0.05) and mortality was low in all treatments. Changes in some measures of thyroid status were apparent in PCB-exposed fish held in the 12 and 16 degrees C treatments while other measures showed no change in any treatment. The natural inverse relationship between thyroid epithelial cell height (TECH) and temperature, was diminished after 30 days of exposure to PCBs as the epithelial cell height in PCB-exposed fish was significantly augmented in the 12 and 16 degrees C treatments compared to controls at these temperatures (p<0.05). However, after 20 days of depuration, TECH values in the PCB exposed fish returned to control values. The natural linear gradient between T(4) outer-ring deiodinase activity (ORD) and temperature was also diminished after 30 days of exposure to PCBs. PCB-exposed fish from the 16 degrees C treatment had significantly lower deiodinase activities (p<0.05) compared to controls at this temperature, but deiodinase activities returned to normal by day 20 of depuration. No differences were observed in T(3) inner-ring deiodinase (IRD) activities and plasma concentrations of T(3) and T(4) in any of the treatments (p>0.05). EROD activity in fish from the CYP1A and CYP2 treatments were elevated compared to control and high dose PCB-exposed treatments (p<0.05), but the inclusion of CYP inducing congeners did not appear to influence any index of thyroid status. Results of this study suggest that exposure of rainbow trout to high concentrations of PCBs and/or OH-PCBs may alter some indices of thyroid status when water temperatures are high, but these changes are within the compensatory scope of the thyroid system based on no change in circulating hormone concentrations, growth rates or mortality.     

Abamectin effects on rainbow trout (Oncorhynchus mykiss)

The effect of abamectin (ABM) on rainbow trout (Oncorhynchus mykiss) was studied. The acute toxicity of ABM on rainbow trout was established, following the target 58-h water bath exposure of ABM concentrations from 0.6 to 4.5 μg/l, on the basis of which LD₇₅ (4.0 μg/l) was calculated. The histological changes in organs showed a direct toxicity of ABM for rainbow trout since degenerative changes in brain and kidney and—to a minor extent—in liver were established. The values of the ABM residues in fish muscle tissue with skin were proportional to the exposed concentrations of ABM.     

Biomarker analyses in caged and wild fish suggest exposure to pollutants in an urban area with a landfill

An unexpectedly high frequency of skeletal deformations in brown trout has previously been observed in the brook Vallkärrabäcken in southern Sweden. Environmental pollutants from storm water and leachate from an old landfill have been suggested as responsible for the observed deformations. Biomarkers in farmed rainbow trout, placed in tanks with water supplied from the brook, were used to investigate if exposure to pollutants may induce toxic responses in fish. Furthermore, biomarkers were also measured in wild brown trout that were caught in the brook. The most important finding was that the hepatic ethoxyresorufin‐O‐deethylase (EROD) activity was five to seven times higher for rainbow trout and brown trout in exposed areas compared to reference sites (P < 0.001). Analyses of bile in rainbow trout showed that the concentration of PAH‐metabolites was two to three times higher (P < 0.001) in the exposed areas. However, due to their smaller size and the feeding status, only insufficient amounts of bile could be retrieved from the wild brown trout. The study provides evidence for pollution in parts of Vallkärrabäcken. It is therefore possible that the previously observed high frequency of skeletal damage have been caused by pollutants. The methodology with farmed rainbow trout in flow through tanks worked well and provided more information about the occurrence of pollutants in Vallkärrabäcken than the data from brown trout. The main reasons for this were that the size and the feeding status of the fish could be controlled. This allowed a total of 21 biomarkers to be analyzed in farmed rainbow trout compared to only five in wild brown trout. Furthermore, the use of farmed fish eliminates the risk of migration, which may otherwise bias the data when wild fish are used. © 2010 Wiley Periodicals, Inc. Environ Toxicol, 2011.