Hydromineral balance in the marine gulf toadfish (Opsanus beta) exposed to waterborne or infused nickel

The effects of acute Ni exposure on the marine gulf toadfish (Opsanus beta) were investigated via separate exposures to waterborne nickel (Ni) and arterially infused Ni. Of the plasma electrolytes measured after 72 h of waterborne exposure (215.3 and 606.1 microM Ni in SW (salinity of 34)), only plasma [Ca2+] was significantly impacted (approximately 55% decrease at both exposure concentrations). At both exposure concentrations, plasma [Ni] was regulated for 24h, after which a linear accumulation over time occurred. Accumulation of Ni in the plasma, and in tissues in direct contact with seawater (gill, stomach, and intestine), was roughly proportional to the Ni concentration of the exposure water. Hydromineral balance in the intestinal fluid (IF) was markedly impacted, with Na(+), Cl(-), SO(4)(2-), K+, and Mg2+ concentrations elevated after 72 h of exposure to waterborne Ni. Following arterial Ni infusion (0.40 micromolNikg(-1)h(-1)), perturbation of hydromineral balance of the intestinal fluid was specific only to Na+ (significantly elevated by Ni infusion) and Mg2+ (significantly decreased by Ni infusion). Nitrogen excretion was not significantly impacted by Ni infusion. In all tissues save the kidney, Ni accumulation via infusion was only a fraction of that observed during waterborne exposures. Remarkably, the kidney Ni burden following infusion was almost identical to that resulting from both waterborne exposures, suggesting homeostatic control. Ni excretion, dominated at 24 h by extrarenal routes, was primarily a function of renal excretion by 72 h of infusion. The sum excretion from infused toadfish was relatively efficient, accounting for over 40% of the infused dose by 72 h. Mechanistic knowledge of the mechanisms of toxicity of waterborne Ni in marine systems is a critical component to the development of physiologically based modeling approaches to accurately predict Ni toxicity in marine and estuarine ecosystems.     

An ultrastructural study of chromate-induced hyperplasia in the gill of rainbow trout (Salmo gairdneri)

Fingerling trout (Salmo gairdneri) were exposed to chromate at pH 6.5 to induce hyperplasia of the gill epithelium. Morphological and ultrastructural data indicate that the hyperplastic reaction starts locally in the primary and the secondary epithelium. Upon prolonged exposure to chromate, hyperplastic cells fill all interlamellar spaces and cover a number of clustered primary lamellae. The hyperplasia seems to result from direct chromate damage to the mucosal epithelium, triggering increased mitotic activity in underlying cells. Simultaneously, some of the newly formed epithelial cells differentiate into chloride and mucus cells. The balance between cell death and mitosis determines the degree of hyperplasia. Upon termination of the exposure to chromate, the hyperplasia disappears in gills of those fish that survive the respiratory and osmoregulatory dysfunction caused by the malformation of the gill lamellae.     

Acute waterborne nickel toxicity in the rainbow trout (Oncorhynchus mykiss) occurs by a respiratory rather than ionoregulatory mechanism

The acute mechanism of toxicity of waterborne nickel (Ni) was investigated in the rainbow trout (Oncorhynchus mykiss) in moderately hard ( approximately 140 mg l(-1) as CaCO(3)) Lake Ontario water, where the 96-h LC(50) for juvenile trout (1.5-3.5 g) was 15.3 mg (12.7-19.0, 95% C.L.) dissolved Ni l(-1). No marked impact of Ni exposure on average unidirectional or net fluxes of Na(+), Cl(-), or Ca(2+) was observed in juvenile trout exposed for 48-60 h to 15.6 mg Ni l(-1) as NiSO(4). Furthermore, when adult rainbow trout (200-340 g) were fitted with indwelling dorsal aortic catheters and exposed for 117 h to 11.6 mg Ni l(-1) as NiSO(4), plasma ions (Na(+), Cl(-), Ca(2+), and Mg(2+)) were all well conserved. However, mean arterial oxygen tension dropped gradually to approximately 35% of control values. This drop in P(aO(2)) was accompanied by an acidosis primarily of respiratory origin. P(aCO(2)) rose to more than double control values with a concomitant drop in arterial pH of 0.15 units. Acute respiratory toxicity was further evidenced by a significant increase in hematocrit (Ht), and plasma lactate, and a significant decrease in spleen hemoglobin (Hb). Following 117 h of exposure to 11.6 mg Ni l(-1), the gill, intestine, plasma, kidney, stomach, and heart accumulated Ni significantly, with increases of 60, 34, 28, 11, 8, and 3-fold, respectively. Brain, white muscle, liver, and bile did not significantly accumulate Ni. Plasma Ni exhibited a remarkable linear increase with time to levels approximately 30-fold higher than controls. We conclude that in contrast to most other metals, Ni is primarily a respiratory, rather than an ionoregulatory, toxicant at exposure levels close to the 96-h LC(50). The implications of a waterborne metal as an acute respiratory toxicant (as opposed to ionoregulatory toxicants such as Cu, Ag, Cd, or Zn) with respect to toxicity modeling are discussed.     

Gill EROD in monitoring of CYP1A inducers in fish: a study in rainbow trout (Oncorhynchus mykiss) caged in Stockholm and Uppsala waters

The gill filament 7-ethoxyresorufin O-deethylase (EROD) assay was evaluated as a monitoring tool for waterborne cytochrome P4501A (CYP1A) inducers using rainbow trout (Oncorhynchus mykiss) caged in urban area waters in Sweden. To compare the CYP1A induction response in different tissues, EROD activity was also analyzed in liver and kidney microsomes. Immunohistochemistry was used to localize CYP1A protein in gill and kidney. In two separate experiments fish were caged at sites with fairly high expected polyaromatic hydrocarbon (PAH) contamination. In the first experiment, gill EROD activities were analyzed in fish exposed for 1-21 days in a river running through Uppsala. The reference site was upstream of Uppsala. In the second, gill, liver and kidney EROD activities were analyzed in fish exposed for 1-5 days in fresh or brackish waters of Stockholm and in a reference lake 60km north of Stockholm. Fish exposed for 5 days followed by 2 days of recovery in tap water in the laboratory were also examined. The gill consistently showed a higher EROD induction compared with the liver and the kidney. After 1 day of caging, gill EROD activity was markedly induced (6-17-fold) at all sites examined. Induction in gill was pronounced (5-7-fold) also in fish caged at the reference sites. In the 21-day exposure study gill EROD activity remained highly induced throughout the experiment (26-fold at most) and the induced CYP1A protein was exclusively confined to the gill secondary lamellae. In the 5-day exposure experiment, EROD activity peaked after 1 day and then declined in both gill and liver, while CYP1A immunostaining in the gill remained intense over the 5-day period. In the kidney, CYP1A staining was weak or absent. We conclude that gill EROD activity is a more sensitive biomarker of exposure to waterborne CYP1A inducers than EROD activity in liver and kidney.     

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.     

Effects of short-term copper exposure on gill structure, metallothionein and hypoxia-inducible factor-1alpha (HIF-1alpha) levels in rainbow trout (Oncorhynchus mykiss)

Rainbow trout (Oncorhynchus mykiss) were exposed to 1.65 microM of waterborne copper for 24 h. Fish were then transferred to metal-free water. Metallothionein mRNA induction in rainbow trout liver and gill tissue, hypoxia-inducible factor-1 (HIF-1alpha) accumulation in gill tissue and arithmetic mean thickness of gill epithelium (Har) were determined at 4 and 24h of exposure as well as 48 h after transfer to metal-free water. The arithmetic mean distance from water to blood was significantly elevated after both 4 and 24 h of exposure (Har was 4.67 and 4.66 microm, respectively in exposed fish, compared to 3.81 and 3.62 microm for the corresponding control fish). During the 48 h recovery Har returned towards the control values; the recovery value of 4.21 microm was significantly lower than values during exposures. There was also a significant increase in gill metallothionein mRNA levels after the 4 h exposure with MT/GAPDH ratio of 1.288 versus the control value of 0.988. In liver, metallothionein induction was not observed. HIF-1alpha protein showed an increased accumulation in gills after 4 h, with the HIF-1alpha/alpha-tubulin ratio of 0.562 being significantly higher than the 24 h exposure value of 0.232. These results suggest that exposure to copper for four hours causes hypoxia in the gill epithelium, which is adequate for the activation of HIF-1alpha.     

The time course of silver accumulation in rainbow trout during static exposure to silver nitrate: physiological regulation or an artifact of the exposure conditions?

The pattern of gill silver accumulation in rainbow trout during waterborne silver exposure has been reported to be unusual, reaching a peak in the first few hours of silver exposure followed by a marked decline with continued exposure. The potential causes of the pattern were investigated. Rainbow trout (1-5g) were exposed in a static system to 110mAg labeled AgNO(3) at a total concentration of 1.92microg Agl(-1) for 24h in synthetic soft water. Periodically throughout the exposure, gill and body 110mAg accumulation, gill and body 24Na uptake (from which whole body Na(+) uptake was calculated), gill Na(+)K(+)-ATPase activity, plus water silver (total and dissolved), Cl(-) and total organic carbon (TOC) concentrations were measured. Gill silver levels rapidly increased, peaked at 3h of exposure and then decreased until a plateau was reached at 12h of exposure. Body (minus gills) silver levels increased steadily over the exposure period until 18h of exposure. Whole body Na(+) uptake decreased, was maximally inhibited by 3h of exposure but recovered by 12h despite continued silver exposure. Gill Na(+)K(+)-ATPase activity was not inhibited until 5h of exposure. The water dissolved silver concentration declined by approximately 70% over the 24h exposure period and the TOC content of the water increased over three-fold during the first 2h of exposure. There was a decrease in the calculated contribution of Ag(+) (from 20.9 to 2.5%) and an increase in the calculated contribution of Ag-TOC complexes (from 77 to 97.3%) to the total water silver concentration over the first 2h of exposure. Apical silver uptake into the gills decreased over the initial 2.5h of exposure while basolateral silver export out of the gills to the body remained constant throughout the exposure. The results of this study suggest that: (1) physiological regulation of silver movement may explain the pattern of gill silver accumulation observed in rainbow trout, although not by a mechanism coupled to Na(+)K(+)-ATPase inhibition as originally proposed; (2) alternatively or additionally, a decreased bioavailability of silver, due to the static exposure conditions, may explain the pattern of gill accumulation; (3) the early inhibition of whole body Na(+) uptake observed during silver exposure occurs via a mechanism other than Na(+)K(+)-ATPase inhibition; and (4) gill silver accumulation may be an appropriate endpoint for biotic ligand modeling.     

Effects of copper on cortisol receptor and metallothionein expression in gills of Oncorhynchus mykiss

Effects of waterborne Cu (2.4 microM) on the expression of glucocorticoid receptor (GR) and metallothionein (MT) in the branchial epithelium of freshwater rainbow trout (Oncorhynchus mykiss) was studied by immunocytochemistry. After 5 days of Cu exposure, the number of GR-immunoreactive (GR-ir) cells in the gill epithelium had decreased, whereas the number of MT-ir cells had increased. Localization of GR in chloride cells was achieved by double staining for Na(+)/K(+)-ATPase; other cell types were identified on the basis of their topology. GRs were present in the chloride cells in both the filaments and lamellae, in respiratory cells in the lamellae, in pavement cells, basal layer cells and undifferentiated cells in the filaments. Co-localization of Na(+)/K(+)-ATPase and MT revealed chat MT was expressed in chloride cells, both in filaments and lamellae. Occasionally, MT immunoreactivity was found in pavement cells and in undifferentiated cells. By double staining for Na(+)/K(+)-ATPase and GR, for Na(+)/K(+)-ATPase and MT and for GR and MT, we can conclude that after 5 days of Cu stress there are chloride cells that express GR and MT, GR or MT alone or neither of the two proteins. This apparent functional heterogeneity of branchial chloride cells may reflect a limited window when chloride cell subpopulations show an adaptive response to Cu.     

Sensitivity of the spiny dogfish (Squalus acanthias) to waterborne silver exposure

The physiological effects of waterborne silver exposure (added as AgNO(3)) on spiny dogfish, Squalus acanthias, were evaluated at 30, 200 and 685 microg silver per l in 30 per thousand seawater. These concentrations cover the toxic range observed for freshwater teleosts, where silver is extremely toxic, to seawater teleosts which tolerate higher silver concentrations. However, these levels are considerably higher than those that occur in the normal environment. At 685 microg l(-1), dogfish died within 24 h. Causes of death were respiratory as well as osmoregulatory failure. Arterial P(a)O(2) rapidly declined below 20 Torr, and blood acidosis (both respiratory and metabolic) occurred. Urea excretion increased dramatically and plasma urea dropped from 340 to 225 mM. There were pronounced increases in plasma Na(+), Cl(-), and Mg(2+), indicative of ionoregulatory failure due to increased diffusive permeability as well as inhibited NaCl excretion. At 200 microg l(-1), fish died between 24 and 72 h of silver exposure. The same physiological events occurred with a small time delay. At 30 microg l(-1), effects were much less severe, although slight mortality (12.5%) still occurred. Respiratory alkalosis occurred, together with moderate elevations in plasma Na(+) and Cl(-) levels. Silver accumulated to the highest concentrations on gills, with only low levels in the intestine, in accord with the virtual absence of drinking. Na(+)/K(+)-ATP-ase activities of gill and rectal gland tissue were impaired at the highest silver concentration. Normal gill function was impaired due to swelling and fusion of lamellae, lamellar aneurism and lifting of the lamellar epithelium. Our results clearly indicate that this elasmobranch is much more sensitive (about 10-fold) to silver than marine teleosts, with silver's toxic action exerted on the gill rather than on the intestine, in contrast to the latter.     

A physiologically based toxicokinetic model for lake trout (Salvelinus namaycush)

A physiologically based toxicokinetic (PB-TK) model for fish, incorporating chemical exchange at the gill and accumulation in five tissue compartments, was parameterized and evaluated for lake trout (Salvelinus namaycush). Individual-based model parameterization was used to examine the effect of natural variability in physiological, morphological, and physico-chemical parameters on model predictions. The PB-TK model was used to predict uptake of organic chemicals across the gill and accumulation in blood and tissues in lake trout. To evaluate the accuracy of the model, a total of 13 adult lake trout were exposed to waterborne 1,1,2,2-tetrachloroethane (TCE), pentachloroethane (PCE), and hexachloroethane (HCE), concurrently, for periods of 6, 12, 24 or 48 h. The measured and predicted concentrations of TCE, PCE and HCE in expired water, dorsal aortic blood and tissues were generally within a factor of two, and in most instances much closer. Variability noted in model predictions, based on the individual-based model parameterization used in this study, reproduced variability observed in measured concentrations. The inference is made that parameters influencing variability in measured blood and tissue concentrations of xenobiotics are included and accurately represented in the model. This model contributes to a better understanding of the fundamental processes that regulate the uptake and disposition of xenobiotic chemicals in the lake trout. This information is crucial to developing a better understanding of the dynamic relationships between contaminant exposure and hazard to the lake trout.     

Tissue-specific cadmium and metallothionein levels in freshwater crab Sinopotamon henanense during acute exposure to waterborne cadmium

The freshwater crabs Sinopotamon henanense were exposed to different concentrations of waterborne cadmium (Cd). The relationship between tissue-specific Cd accumulation and metallothionein (MT) induction was investigated using the Cd saturation assay and atomic absorption spectrophotometry method. The results showed that Cd accumulation rose significantly in all tissues studied after Cd exposure, and the Cd accumulation level in various tissues followed the following order: gill > hepatopancreas > muscle > ovary. MT levels were clearly tissue-specific after Cd exposure. Hepatopancreas was found to have the highest MT level, followed by the gill, muscle, and ovary. In conclusion, the results indicated although Cd exposure clearly resulted in MT induction, its synthesis does not correlate with Cd accumulation in the later stage of Cd exposure. The calculated ratios of actual Cd to theoretical maximum Cd-MT in the hepatopancreas were <1.0 under acute waterborne Cd at all sampling points, indicating that the hepatopancreas had much greater Cd-binding potential of MT than the gill, muscle, or ovary. It is clear from our results that a positive correlation was shown between MT induction and Cd accumulation both in hepatopancreas and gill. Therefore, MT induction can be considered as a biomarker for acute waterborne Cd pollution.     

Sublethal effects of commercial deltamethrin on the structure of the gill, liver and gut tissues of mosquitofish, Gambusia affinis: A microscopic study

The histopathological effects of deltamethrin on the gill, liver and gut tissues of the mosquitofish, Gambusia affinis were determined by light microscopy. The fish were exposed to two sublethal concentrations of deltamethrin (0.25–0.50 μg/l) for periods of 10, 20 and 30 days. The most common gill changes at all doses of deltamethrin were desquamation and necrosis. Besides, epithelial hypertrophy, lifting of the lamellar epithelium, oedema, dilatation of the capillaries primary lamellae, aneurism, epithelial hyperplasia and fusion of the secondary lamellae were other histopathological effects. Hepatic lesions in the liver tissues of fish exposed to deltamethrin were characterized by hypertrophy of hepatocytes, significant increase of kupffer cells, circulatory disturbances, focal necrosis, fatty degeneration, nuclear pycnosis and narrowing of sinusoids. Infiltration of mononuclear leucocyte and eosinophils towards lamina propria, necrosis were detected in gut tissues of fish after exposure to deltamethrin.     

Presystemic branchial metabolism limits di-2-ethylhexyl phthalate accumulation in fish

Despite the high lipophilicity of di-2-ethylhexyl phthalate (DEHP), fish do not extensively accumulate this ubiquitous environmental contaminant. Experiments with rainbow trout (Salmo gairdneri) fitted with an indwelling cannula showed that the majority of [14C]DEHP did not reach the systemic circulation of the fish, but was present in the exposure water as metabolites. Pharmacokinetic analysis, using a compartmental model that included the gill as a separate metabolic compartment, indicated that DEHP was extensively metabolized as it diffused from water to blood. Isolated perfused gill arches of trout metabolized DEHP in the exposure bath to monoethylhexyl phthalate, demonstrating the ability of the gill to prevent DEHP entry into the fish. The relationship between metabolic clearance and tissue perfusion further suggests that metabolism in the gill can play an important role in determining the accumulation and toxicity of organic chemical pollutants in fish.     

Atorvastatin up-regulate toxicologically relevant genes in rainbow trout gills

There are large and increasing discharges of statins into the aquatic environment. Statins are cholesterol-lowering pharmaceuticals, inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A reductase, an enzyme in the cholesterol synthesis pathway. Earlier studies have shown that statins will affect the expression of a range of genes in mammalian tissues and this group of pharmaceuticals has also been shown to affect membrane transporters. Changes in gene expression and ion transport in aquatic organisms may have dramatic consequences for the individual. The aim of the present study was to clarify whether waterborne exposure to a selected statin, atorvastatin, would affect gene expression in rainbow trout (Oncorhynchus mykiss) gill or liver or ion regulation in gills. Juvenile rainbow trout were exposed to two atorvastatin acid and atorvastatin lactone concentrations for 7?days (nominal concentrations 200?ng?L(-1) and 10?μg?L(-1)). The exposures caused up-regulated gene expression in gill, not liver, and only at the lowest concentration. Genes involved in membrane transport (pgp, mrp1), oxidative stress response (sod, mt), apoptosis (bax) and biotransformation (sult2b) were differentially expressed whereas the expression of genes involved in cholesterol biosynthesis (hmgr, fdps) or peroxisomal proliferation (ppar) were not affected. There were no significant changes in gill Na(+)/K(+) ATPase activity following exposure to atorvastatin. The pattern of differentially expressed genes in rainbow trout gills differ from responses previously observed in mammalian tissues following statin exposure.     

Swimming performance and energy metabolism of rainbow trout, common carp and gibel carp respond differently to sublethal copper exposure

We compared the effects of sublethal waterborne copper exposure on swimming performance and respiration rates in rainbow trout, Oncorhynchus mykiss, with those in less sensitive cyprinid species such as common carp, Cyprinus carpio, and gibel carp, Carassius auratus gibelio. These cyprinids are considerably more resistant to Cu intoxication, and differ from trout in swimming performance and respiratory behaviour. Critical swimming speed (U(crit)), oxygen consumption, plasma ammonia and muscle ammonia, lactate and pH were measured during a 28-day sublethal exposure to 1 microM Cu. U(crit) decreased with 48, 31 and 13% within the first 12-24 h for rainbow trout, common and gibel respectively. Gibel carp recovered quickly and experienced no further reduction in swimming performance. Recovery of swimming capacity in rainbow trout and common carp was only partial. All three species displayed similar plasma ammonia peaks in the first hours to days, and a more gradual muscle ammonia accumulation over time. Whereas no signs of respiratory stress occurred in rainbow trout, common carp experienced a transient reduction in oxygen consumption combined with anaerobic metabolism after 24 h of exposure. At the same time, oxygen consumption was also reduced in gibel carp, but no signs of anaerobic metabolism were detected. Cu accumulated quickly to similar levels (36-39 microg g(-1) dry weight at day 3) in the gills of all three species, after which accumulation leveled off. Liver tissue of rainbow trout had a high Cu level from the start, and Cu concentration did not show any additional accumulation. In contrast, common carp liver showed a significant Cu accumulation from day 3 onwards, while accumulation in gibel livers was much slower and was significant from day 7 onwards. Interestingly, Cu accumulation patterns in plasma and kidney revealed a possibly important role for the kidney in Cu homeostasis of gibel carp.     

Differential metallothionein induction patterns in three freshwater fish during sublethal copper exposure

We assessed whether fish that tolerate higher levels of Cu exposure have a higher capacity to induce metallothionein (MT) synthesis than other, more sensitive, fish species. Furthermore, we examined if a correlation could be found between tissue Cu accumulation and MT levels. Cu accumulation and MT concentrations in gill, liver, kidney and muscle of rainbow trout (Oncorhynchus mykiss), common carp (Cyprinus carpio) and gibel carp (Carassius auratus gibelio) were measured during a 1 week exposure to a sublethal Cu (1 microM). Different patterns were observed for the three species regarding Cu accumulation as well as MT induction. Virtually no Cu accumulation was seen in rainbow trout gill, while in both cyprinid species gill Cu levels increased three- to four-fold. Cu accumulated fast in common carp (within the first day), but slow in gibel carp (1 week). Gill MT induction was obvious in gibel carp only, with an increase of 156% after 1 week of exposure. Liver accumulated most Cu in rainbow trout (235% increase) and common carp (144% increase), with Cu levels in liver being significantly higher in rainbow trout compared to the carp species from the start. MT induction was pronounced in common carp liver only (138% increase). In gibel carp liver, there was no clear Cu accumulation or MT induction. In contrast, gibel carp was the only species to show Cu accumulation in kidney after 3 days of exposure (83% increase), after which levels returned to normal. Concomitantly, gibel carp kidney was also the only kidney tissue to show MT induction (192-195% increase after 3 and 7 days). In common carp, a significant decrease of kidney MT levels was observed from day 1 onwards. In muscle, Cu accumulation was clear for the two cyprinid species (three- to four-fold increase) but not for rainbow trout. Of the species studied, gibel carp is the most resistant to copper polluted environments, and showed a positive significant relationship between tissue copper concentrations and MT levels in gill, liver and muscle tissues. Common carp showed an intermediate response, with significant correlations in liver and muscle tissue. In contrast, we found low MT induction in rainbow trout, the most sensitive species, and no correlation at all between MT concentrations and tissue copper contents. Possibly, the regulatory capacity for copper homeostasis was exceeded in rainbow trout, and MT synthesis inhibited.     

Food selection, growth and physiology in relation to dietary sodium chloride content in rainbow trout (Oncorhynchus mykiss) under chronic waterborne Cu exposure

Waterborne Cu is toxic to Na(+) and Cl(-) regulation in freshwater fish, and Cu is taken up, at least in part, via the Na(+)-transport pathway in the gills. Therefore, we hypothesized that freshwater fish may mitigate the toxic effects of waterborne Cu by selecting a NaCl-enriched diet over a normal diet. We tested this hypothesis in juvenile rainbow trout (Oncorhynchus mykiss) by offering them the choice between NaCl-enriched (1.9 mmol g(-1)Na(+)) and normal (0.2 mmol g(-1)Na(+)) diets under a chronic waterborne Cu exposure of 55 microg L(-1) for a period of 28 days. Contrary to expectation, trout exhibited a preference for NaCl-enriched diet under control conditions, while exposure to chronic waterborne Cu severely disrupted their normal feeding pattern with an accompanying loss of preference for the NaCl-enriched diet. Waterborne Cu exposure also severely affected appetite and growth. Both appetite and growth gradually recovered with time, but remained significantly impaired relative to Cu-unexposed fish until the end of the exposure. Waterborne Cu exposure also significantly increased Cu accumulations in target organs (gill, liver, and gut), plasma and whole body. However, Cu accumulation decreased substantially towards the end of the exposure in target organs and whole body as well as in plasma in Cu-exposed fish with dietary choice relative to Cu-exposed fish with normal diet. These adjustments were concurrent with the gradual recovery of appetite, which also led to increased ingestion of the NaCl-enriched diet. Interestingly, this elevated dietary uptake of NaCl produced significant stimulation of Na(+) efflux in Cu-exposed fish. Subsequently, it also led to significant elevation of Na(+) levels in target organs and whole body, and restored the decrease of plasma Na(+) and Cl(-) levels in Cu-exposed fish. The NaCl supplemented diet appeared to be beneficial in compensating Na(+) and Cl(-) losses from the body induced by waterborne Cu. Overall, these results demonstrate that a NaCl-enriched diet, although consumed in relatively reduced quantities due to the impairment of food selection and appetite, can help to protect freshwater fish against chronic waterborne Cu toxicity.     

Effects of temperature on the recovery of juvenile grayling (Thymallus thymallus) from exposure to Al+Fe

One-summer-old graylings (Thymallus thymallus) were exposed for 6 days to water containing a mixture of 1 mg l(-1) Fe and 100 microg l(-1) Al at pH 5.5, with or without 15 mg l(-1) humic acid. A pH of 6.9 was used as a control. The experiment was performed at two test temperatures, 13 and 3 degrees C. After 1 week of exposure, half of the fish in the tank were taken for oxygen measurement and tissue sampling. The remaining half were maintained in metal-free water for a further week to assess their recovery at the two test temperatures. Fifty percent of the fish died under metal exposure at 13 degrees C, but none at 3 degrees C. Despite of the lack of mortalities at the lower temperature, surviving fish at both test temperatures suffered similar gill damage (adherence of lamellae), disturbances in ion regulation, increases in haematocrit value (Hct) and haemoglobin (Hb) concentration and reductions in oxygen consumption. The addition of humic acid prevented these changes. The reduced plasma chloride concentration, increased blood Hct value and Hb concentration recovered completely at 13 degrees C, whereas the lowered oxygen consumption recovered less completely, which may be attributed to the remaining minor gill damage (lamellar hypertrophy). At the lower temperature, the adherence of lamellae persisted after the recovery period, and oxygen consumption, therefore, remained at a very low level. The decreased plasma chloride concentration was also unable to recover. The accumulation of Al inside the gill tissue was greater at low temperature. We conclude that the acute toxicity of a mixture of Fe and Al to grayling and their subsequent ability to recovery is dependent on the exposure temperature.