Toxicity In Rainbow Trout Research Articles

Silver nanoparticle toxicity in rainbow trout: insights into physiological and molecular responses.

Metallic nanoparticles, with their large surface area to volume ratio, are increasingly important in various life fields, but they can cause varying toxic effects on fish. This study investigates the toxicological effects of silver nanoparticles (AgNPs) on rainbow trout (Oncorhynchus mykiss), focusing on hematological, biochemical, antioxidant, and histopathological changes. Fish were exposed to varying concentrations of AgNPs (0.2, 0.8, and 1.4 mg/L) for 21days. Hematological analysis revealed significant reductions in red blood cell (RBC) counts, hemoglobin (Hb), and hematocrit (HCT) at higher AgNPs concentrations, while white blood cell (WBC) counts increased, indicating immune system activation. Biochemical assays demonstrated dose-dependent decreases in total protein and albumin, alongside increased cholesterol and triglyceride levels, suggesting impaired liver function and disrupted lipid metabolism. Antioxidant enzyme activity (SOD, CAT, GST) initially increased at lower AgNPs concentrations but declined at higher exposures, indicating oxidative stress. Molecular analysis further supported these findings, with upregulation of oxidative stress-related genes (SOD1, CAT) and inflammatory markers (HSP70, IL-1β). Histopathological examinations revealed necrosis, hyperplasia, and lamellar fusion in the gills, along with significant liver damage, including vacuolation and Kupffer cell proliferation, particularly at the highest exposure. Behavioral assays showed erratic swimming and reduced feeding in fish exposed to higher AgNPs concentrations. This study highlights the dose-dependent toxic effects of AgNPs on rainbow trout and underscores the potential for long-term, possibly irreversible damage at higher exposure levels. These findings emphasize the need for stricter environmental regulations on nanoparticle use to mitigate their ecological impact.

EVALUATION OF OXIDATIVE/NITROSATIVE STRESS BIOMARKERS IN KIDNEY, HEART AND MUSCLE TISSUES OF Oncorhynchus mykiss (WALBAUM, 1792) TREATED WITH MERCURY CHLORIDE (HgCl2)

The widespread presence of mercury (Hg) and its derivatives in aquatic environments necessitates the investigation of their toxic effects on fish and the potential risks they pose to the health of local populations. The objective of this study was to investigate the toxic effects of mercury chloride (HgCl2) on Oncorhynchus mykiss (Walbaum. 1792) by examining the dynamics of oxidative and nitrosative stress in muscle, kidney, and heart tissues. The rainbow trout used in the study had an average weight of 125.65±8.30 g. Five experimental groups were created, including a control group and groups exposed to 25% LC50 concentration of HgCl2 for 7 and 14 days, as well as groups exposed to 50% LC50 concentration of HgCl2 for 7 and 14 days. A total of 120 fish, with 40 fish assigned to each tissue (muscle, kidney, and heart), were used in the study. To evaluate oxidative/nitrosative stress, various parameters including ONOOˉ, TOS, TAS, OSI, and MDA levels were measured. Statistical analysis revealed a significant difference between the experimental groups in terms of TAS, TOS, OSI, ONOOˉ, and MDA levels in all three tissues (muscle, kidney, and heart) (P<0.05). In conclusion, the findings of this study demonstrate that HgCl2 induces stress and toxicity in rainbow trout, as evidenced by increased levels of MDA and ONOOˉ, which are stress indicators in the fish.

Does hydrogen-rich water mitigate MP toxicity in rainbow trout (Oncorhyncus mykiss)? Monitoring with hematology, DNA damage, andapoptosis via ROS/GSH/MDA pathway

Although the number of studies documenting the presence of Microplastics (MP) in fish is increasing, research studies focused on its detoxification are very limited. In this study, rainbow trout (Oncorhyncus mykiss) were randomly divided into two groups after being fed with MPs (15% polypropylene [PP] +15% polyethylene [PE]) for 2 months. MP excretion without any application (PP+PE) in group I fish, and excretion of MPs with hydrogen-rich water (HRW) application (PP+PE+HRW) in group 2 were investigated under semi-static conditions for 21 days. This effectwas also compared by using positive and negative control groups (Control[no treatment, free PP, PE or/and HRW] and only HRW group). In this direction, the following were determined: PP+PE chronic toxicity in aquatic organisms, the toxicity mechanism and the effect of HRW as a possible treatment method in blood tissue; with hematological indices ([RBC count[RBC], leukocyte count [WBC], hemoglobin value [Hb], hematocrit ratio[Hct], platelet count [PLT], hemoglobin count per erythrocyte [MCHC], mean hemoglobin amount per erythrocyte [MCH] and mean erythrocyte volume [MCV]) in other tissues (liver, gill and brain tissue) oxidative stress response (catalase [CAT]), glutathione peroxidase (GPx), glutathionereductase (GR), superoxide dismutase (SOD), glutathione (GSH), reactiveoxygen products (ROS), malondialdehyde ([MDA] levels), DNA damage(8-OHdG: 8-Hydroxy-2-Deoxyguanosine), and the apoptosis (caspase 3)levels were investigated. In addition, acetylcholinesterase enzyme (AChE)activity, which is important in neurotoxicity pathways in the brain, was determined. The presence of plastics (PP/PE) in target tissues (muscle, liver, gill and gastrointestinal tract) was also obtained.The results showed that PP+PE caused toxicity in all three tissues. MPs showed an inhibiting effect on antioxidant enzyme activities and an inductive effect on MDA, ROS, 8-OHdG, and caspase 3 levels. HRW showed a mitigating effect on MP-mediated toxicity in O. mykiss brain, blood, gill, and liver by controlling the ROS/ GSH/MDA pathway. HRW can be suggested as a cost-effective and eco-friendly curative for the protection of fish from the oxidative damages produced by the ingestion of microplastics.

Effects of encapsulation of Lactobacillus plantarum on probiotic potential and reducing lead toxicity in rainbow trout (Oncorhynchus mykiss Walbaum)

Effects of encapsulation of Lactobacillus plantarum on probiotic potential and reducing lead toxicity in rainbow trout (Oncorhynchus mykiss Walbaum)

Protective effects of dietary Lavender (Lavandula officinalis) essential oil against Malathion-induced toxicity in rainbow trout (Oncorhynchus mykiss)

Abstract The present study was aimed to evaluate the moderating properties of lavender (Lavandula officinalis) essential oil (LEO) against immunotoxic effects of the organophosphate pesticide, malathion in rainbow trout, Oncorhynchus mykiss. For this purpose, fish were supplemented with LEO at dietary concentrations of 0.5, 1, 2 and 4 ml/kg diet LEO for 56 days. A non-LEO supplemented group was also considered as control. After 57 days feeding trial, biochemicals were assayed in the blood and kidney tissue and then fish exposed to a sub-lethal concentration of malathion [0.24 mg/l equal to 30% of LC50 (0.8 mg/L)]. After 57 days feeding trial, the serum total immunoglobulin, respiratory burst activity, lysozyme activity and complement activity significantly elevated in fish treated with 1 and 2 ml LEO/kg diet compared to non-LEO supplemented individuals (P<0.01). Such changes were not observed in non-LEO supplemented fish (P>0.01). Significant elevations were observed in the expression of the immune genes (iNOS and C3 genes) in fish treated with 0.2–2 mg LEO/kg diet compared to non-supplemented ones (P<0.01). The lysozyme and complement activity significantly decreased in fish fed 4 ml/kg diet (P<0.01). After exposure to malathion, all immune components significantly declined in control and those treated with 0.5, 1 and 4 ml LEO/kg diet (P<0.01). In contrast, the immunity components exhibited no significant changes in fish treated with 2 ml LEO/kg diet after exposure (P>0.01). The expression of iNOS and C3 genes significantly reduced in control and fish fed 0.5, 1 and 4 ml LEO/kg diet in response to malathion (P<0.05). Furthermore, the expression of these genes showed no significant changes in fish fed with 2 ml LEO/kg diet after exposure (P>0.01). The findings of the present study suggested an immunoprotective role for dietary LEO at optimized dietary concentrations of 1 and 2 ml LEO/kg diet against oxidative stress and toxicity induced by malathion. Nevertheless, LEO at high dietary concentration (4 ml/kg diet) had reducing effects on the fish immunity.

Hypoxemia as the mechanism of acute cationic polymer toxicity in rainbow trout and prevention of toxicity using an anionic neutralizing polymer.

Industrial operations such as surface mining, road building, and aggregate washing result in high concentrations of suspended particles (Total Suspended Solids; TSS) in surface waters which must be treated prior to discharge into fish-bearing waters. A common industrial practice is to add flocculants to improve the efficacy and speed of TSS sedimentation. A significant environmental issue even small amounts of uncomplexed cationic polymer coagulant/flocculant remaining in treated water is highly toxic to fish at very low concentrations (LC50 ∼ 0.3 mg L-1). Fingerling trout (Oncorhynchus mykiss) were exposed to (1) a cationic flocculant (Water Lynx 800 (WL800), (2) a Clearflow neutralizing polymer (CN369), and (3) a combination of WL800 and CN369 at various ratios with measured LC50 as an index of toxicity. Acute toxicity was entirely reversed by addition of the neutralizing polymer at WL800:CN369 ratios >1:1.5mg/L. Furthermore, we demonstrate that the proximal mechanism of acute cationic polymer toxicity is hypoxemia due to accumulation of polymer on the gill epithelia rather than gill damage. Exposure of 0.5mg/L WL800 reduced oxygen consumption by >50% reduction by 12h and this was accompanied by significantly increased blood, brain, and liver [lactate] and [glucose]. The development of an inexpensive amelioration technique preventing cationic polymer toxicity is a significant advancement in surface and industrial water treatment to prevent cationic polymer mediated fish kills.

Transepithelial potential remains indicative of major ion toxicity in rainbow trout (Oncorhynchus mykiss) after 4-day pre-exposure to major salts.

The Multi-Ion Toxicity (MIT) Model uses electrochemical theory to predict the transepithelial potential (TEP) across the gills as an index of major ion toxicity in freshwater animals. The goal is to determine environmental criteria that will be protective of aquatic organisms exposed to salt pollution. In recent studies, TEP disturbances above baseline (ΔTEP) during short-term exposures to major ions have been proven as indicative of their toxicity to fish, in accord with the MIT model. However, the acute 1-h exposures used in these previous studies might not be realistic relative to the 24h or 96h test periods used for toxicity assessment. To address this temporal inconsistency, the current study investigated both the TEP responses to serial concentrations of 10 major salts (NaCl, Na2SO4, NaHCO3, KCl, K2SO4, KHCO3, CaCl2, CaSO4, MgCl2, MgSO4) and plasma ion levels in juvenile rainbow trout after they had been pre-exposed to 50% of the 96h-LC50 levels of these same salts for 4 days. The pre-exposures caused no mortalities. In general, plasma ions (Na+, K+, Ca2+, Mg2+, Cl-) were well-regulated; however, pre-exposure to sulfate salts resulted in the greatest number of alterations in plasma ion levels. TEP responses remained largely similar to those of naïve trout (without salt pre-exposure). All salts caused hyperbolic concentration-dependent increases in TEP that were well-described by the Michaelis-Menten equation. In the pre-exposed trout, the variation of ∆TEP at the 96h-LC50 concentrations was only 2.2-fold, compared to nearly 28-fold variation among the molar concentrations of the various salts at the 96h-LC50s, identical to the conclusion for naïve trout. Overall, the results remove the temporal inconsistency of previous tests and remain supportive of the MIT model. In addition, the recorded alterations in certain plasma ions, baseline TEP, and Michaelis-Menten constants improve our knowledge on specific physiological responses after extended major ion exposure.

Acute waterborne strontium exposure to rainbow trout: Tissue accumulation, ionoregulatory effects, and the modifying influence of waterborne calcium.

Flowback and produced water (FPW) is an end-product of the hydraulic fracturing method of oil and gas extraction that is highly enriched in alkaline earth metals such as strontium (Sr). While Sr concentrations in FPW can exceed toxic thresholds for fish, the accompanying high concentrations of calcium (Ca) in FPW may ameliorate any toxicity. In this study, Sr bioaccumulation and molecular, biochemical, and physiological changes in ionoregulatory endpoints were investigated in rainbow trout (Oncorhynchus mykiss). Exposures were conducted over a 96-h period at Sr concentrations ranging from 1.7 to 1948µM, with effects at the highest Sr exposure concentration also separately examined in waters of varying Ca concentration (10 to 958µM). Plasma and gill Sr burdens increased as a function of increasing waterborne Sr, and accumulation increased further as water Ca concentrations were lowered. Despite this, there was no consistent, dose-dependent effect of Sr on plasma or gill Ca concentrations, although impacts on plasma and branchial sodium (Na) concentrations were observed. Waterborne Sr significantly inhibited branchial Ca2+-ATPase activity, albeit only at the highest tested Sr concentration (1948µM). In exposure treatments where Sr was highly elevated and water Ca was reduced, the hepatic gene expression of Ca signaling receptors β-2 adrenergic receptor (Adrb2) and inositol-1,4,5-triphosphate receptor-2 (Itpr2) were inhibited, highlighting novel potential pathways of Sr toxicity in rainbow trout. Overall, these data indicate that water Ca has a strong effect on Sr bioavailability, but over an acute exposure period there is limited evidence for an effect of Sr on Ca homeostasis. Although Sr is elevated in effluents associated with the oil and gas industry, the co-occurrence of high Ca concentrations might protect freshwater fish against acute effects related to Sr exposure.

ORAL VACCINATION AGAINST YERSINIA RUCKERI: OXIDATIVE STRESS BIOMARKERS IN THE GILLS OF RAINBOW TROUT (ONCORHYNCHUS MYKISS WALBAUM)

The aim of this study was to assess the effect of oral vaccination against Yersinia ruckeri based on oxidative stress biomarkers in the gills of rainbow trout (Oncorhynchus mykiss Walbaum). The vaccine consisted of three Y. ruckeri strains (O1 serotype) that originated from rainbow trout cultured on different farms, where fish exhibited clinical signs of enteric redmouth disease. The concentrated vaccine was incorporated into the fish food; treatment was delivered three times at one-day intervals. Two months after immunization, gills were sampled. The vaccination against Y. ruckeri resulted in non-significant changes in TBARS level as lipid peroxidation marker, aldehydic and ketonic derivatives of oxidatively modified proteins level in the gills of trout at the second month after immunization against Y. ruckeri. A significant decrease in superoxide dismutase activity (by 36%, p = 0.002) compared to untreated controls occurred. The alterations in markers of oxidative stress suggest that antioxidant defenses may contribute to the balance between oxidative modification of proteins and antioxidant defenses in the gills of trout vaccinated against Y. ruckeri. We did not find any alterations in the gills after 60 days of immunization. This is likely a result of long-term adaptation to immunization. Understanding the role of oxidative stress in the tissues of vaccinated trout has important implications for the understanding of the complex physiological changes that occur in immunization and also for improving aquaculture practices to maximize tissue growth and health of vaccinated trout. The oxidative stress biomarkers in the gills were sensitive to vaccination against Y. ruckeri and may potentially be used as biomarkers in evaluating vaccine toxicity in rainbow trout. From a practical point of view, the results may be useful in relation to studies of infections and the development, administration, and uptake of new vaccines applicable to large amounts of fish.

Trans-epithelial potential (TEP) response as an indicator of major ion toxicity in rainbow trout and goldfish exposed to 10 different salts in ion-poor water.

Freshwater ecosystems are facing increasing contamination by major ions. The Multi-Ion Toxicity (MIT) model, a new tool for risk assessment and regulation, predicts major ion toxicity to aquatic organisms by relating it to a critical disturbance of the trans-epithelial potential (TEP) across the gills, as predicted by electrochemical theory. The model is based on unproven assumptions. We tested some of these by directly measuring the acute TEP responses to a geometric series of 10 different single salts (NaCl, Na2SO4, KCl, K2SO4, CaCl2, CaSO4, MgCl2, MgSO4, NaHCO3, KHCO3) in the euryhaline rainbow trout (Oncorhynchus mykiss) and the stenohaline goldfish (Carassius auratus) acclimated to very soft, ion-poor water (hardness 10mg CaCO3/L). Results were compared to 24-h and 96-h LC50 data from the literature, mainly from fathead minnow (Pimephales promelas). All salts caused concentration-dependent increases in TEP to less negative/more positive values, in patterns well-described by the Michaelis-Menten equation, or a modified version incorporating substrate inhibition. The ΔTEP above baseline became close to a maximum at the 96-h LC50, except for the HCO3- salts. Furthermore, the range of ΔTEP values at the LC50 within one species was much more consistent (1.6- to 2.1-fold variation) than the molar concentrations of the different salts at the LC50 (19- to 25-fold variation). ΔTEP responses were related to cation rather than anion concentrations. Overall patterns were qualitatively similar between trout and goldfish, with some quantitative differences, and also in general accord with recently published data on three other species in harder water where ΔTEP responses were much smaller. Blood plasma Na+ and K+ concentrations were minimally affected by the exposures. The results are in accord with most but not all of the assumptions of the MIT model and support its further development as a predictive tool.

Dietary supplementation of garden thyme essential oil ameliorated the deteriorative effects of aflatoxin B1 on growth performance and intestinal inflammatory status of rainbow trout (Oncorhynchus mykiss)

Phytogenics additives have gained considerable attention as efficacious and safe dietary interventions to reduce the toxic effects of aflatoxin B1 contamination in aquatic animals. The present study was conducted to investigate the ameliorative efficacy of Thymus vulgaris essential oil on aflatoxin B1 (AFB1) toxicity in rainbow trout (Oncorhynchus mykiss) in terms of growth performance, innate plasma immune indices and expression of immune related genes. Five experimental diets including a commercial diet as control, control diet +25 ppb AFB1, control diet +50 ppb AFB1, control diet +25 ppb AFB1 + 1% garden thymus essential oil (TEO), and control diet +50 ppb AFB1+ 1% TEO were tested. Triplicate groups of fish averaging 20.77 ± 0.08 g were fed the test diets at a rate of 3% body weight twice daily for 30 days. At the end of the experiment, fish fed TEO supplemented diets showed improved final weight, weight gain, feed conversion ratio and specific growth rates in comparison to groups received AFB1 with no dietary TEO supplementation (P < 0.05). The biochemical (total protein) and innate immune (lysozyme and ACH50) parameters were significantly enhanced in all TEO supplemented groups (P < 0.05). Expression of tumor necrosis factor-alpha, transforming growth factor-β and interleukin-8 were markedly up-regulated following feeding on diet containing high level of AFB1 (P < 0.05). Meanwhile, dietary TEO supplementation ameliorated the increased tumor necrosis factor alpha, transforming growth factor-β and interleukin-8 expression induced by dietary AFB1 contamination (P < 0.05). However, TEO supplementation significantly enhanced interleukin-1β expression (P < 0.05). It can be concluded that, dietary supplementation of 1% TEO can mitigate the AFB1 induced suppression of growth and innate immunity in rainbow trout.

A NMR-based metabonomic study on the ameliorating effects of Ginkgo biloba extract in rainbow trout, Oncorhynchus mykiss exposed to organophosphate pesticide, diazinon

This study was conducted to investigate the ameliorating effects of Ginkgo biloba extract (GE) on diazinon-induced toxicity in rainbow trout from a metabolic point of view using 1H NMR spectroscopy. Fish were divided into two groups including non-diazinon (Non-DZ) and diazinon-exposed (DZ) groups and then supplemented with various dietary levels of GE for 60 days. PLS-DA analysis of blood and liver metabolome confirmed the effects of GE supplementation and exposure to diazinon on separation of the experimental groups. According to loading plot outputs, amino acids, osmolytes and metabolites associated with energy metabolism had more contribution in the separation of the groups. In Non-DZ fish, the levels of almost all amino acids in blood were significantly lower in GE4 treatment (4 g GE/Kg diet) compared to other groups after 60 days feeding trial (P < .01). The levels of glycerol were found to be significantly higher in GE-supplemented fish compared to other groups (P < .01). In DZ groups, the levels of osmolytes including trimethylamine-N-oxide (TMAO), trimethylamine, N,N-Dimethylglycine and betaine decreased in almost all groups compared to corresponding Non-DZ fish (P < .01). Also, the levels of almost all amino acids elevated in control (non-GE-supplemented fish) and treatments GE1 (0.5 g GE/Kg diet) and GE4 (P < .01). The glucose levels also showed significant decreases in control and fish of treatments GE1 and GE4 (P < .01). The levels of lactate significantly decreased in control and treatments GE1, GE2 and GE4 (P < .01). The levels of glycerol and ketone bodies significantly increased in control and groups GE1, GE2 and GE4 (P < .01). Furthermore, the levels of phosphocreatine significantly increased in control and treatments GE1, GE2 and GE4 (P < .01). In Non-DZ fish, the levels of glycerol in liver were significantly higher in GE-supplemented fish compared to other groups (P < .01). In DZ fish, the levels of hepatic succinate increased in control and groups GE1 and GE4 compared to corresponding Non-DZ fish (P < .01). The values of TMAO and trimethylamine decreased in control group (P < .01). However, the levels of N,N-Dimethylglycine decreased in control and fish of treatments GE1, GE2 and GE4 (P < .01). The levels of ketone bodies also showed significant increases in control and treatments GE1 and GE4 (P < .01). The results of the present study showed that ginkgo at optimized dietary levels (1–2 g GE/Kg diet) is capable to ameliorate the toxicity induced by diazinon, mainly through modulating the biochemical pathways related to the metabolism of the amino acids, energetic metabolites and osmolytes.

Effect of Encapsulated Lactobacillus bulgaricus on Innate Immune System and Hematological Parameters in Rainbow Trout (Oncorhynchus mykiss), Post-Administration of Pb.

The present study was conducted to investigate the effects of probiotic and encapsulated Lactobacillus bulgaricus on hematological and immunological factors after lead toxicity in rainbow trout (Oncorhynchus mykiss). Two hundred and forty fish weighing about 16 ± 3.8g were divided randomly in to four groups including two groups which were fed by a diet containing ~ 108CFUg-1Lactobacillus bulgaricus and encapsulated Lactobacillus bulgaricus bacteria and also the third group diet without Lactobacillus bulgaricus. After 45days, in addition to probiotic (~ 108CFUg-1), 500μgkg of lead nitrate was added to the food of the three groups for 21days. The fourth group (control) was first fed to the normal diet for 45days then exposed to Pb. Blood samples were collected at days 45, 52, 59, and 66, and hematological and some immunological parameters were assessed. Results showed that hemoglobin, red blood cells, white blood cells, and lysozyme activity in the two probiotics groups were increased significantly up to 45day (P< 0.05), but followed by a decreasing trend by adding Pb. Complement and bactericidal activity were enhanced significantly in the bulgaricus group (P< 0.05). Respiratory burst activity at day 45 in group bulgaricus had significant increase (P< 0.05) and decreased in all groups particularly after Pb exposure (P< 0.05). The achieved data shows that microencapsulation of probiotics with alginate-chitosan may be a suitable method to improve the fish condition against heavy metal.

Intravenous injection of unfunctionalized carbon-based nanomaterials confirms the minimal toxicity observed in aqueous and dietary exposures in juvenile rainbow trout (Oncorhynchus mykiss).

Numerous ecotoxicology studies of carbon-based nanomaterials (CNMs) have been conducted in fishes; however, different approaches have been used to make CNM dispersions and dose tanks for aqueous exposures, and to prepare food containing CNMs for dietary studies. This diversity of experimental methods has led to conflicting results and difficulties in comparing studies. The objective of the present study was to evaluate intravenous injection of unfunctionalized CNMs in rainbow trout (Oncorhynchus mykiss), as a means of delivering a known internal dose, on tissue biochemistry and histopathological lesions; then, subsequently, to compare the results with our previous work on aqueous and dietary exposures of rainbow trout to CNMs. Rainbow trout were injected in the caudal vein with corn oil dispersions of 200μg (approximately 1μgg-1) of either the fullerene C60, single-walled carbon nanotubes (SWCNTs), or amorphous carbon black. After 96h, injected fish were euthanized and tissue samples collected for biochemistry and histology. Histological examination of the kidney of fish injected intravenously indicated the presence of black material consistent with the injected carbon treatments. However, there were no additional lesions associated with CNM exposure compared to controls. There were also no significant changes in haematology, or ionoregulatory disturbance in blood plasma among the intravenously injected fish. Significant elevation in lipid peroxidation (thiobarbituric acid reactive substances TBARS) was detected only in kidney and spleen of fish injected with SWCNTs, but not the other carbon treatments. The elevated TBARS following injection contrasted with CNMs delivered via aqueous or dietary routes in our previous studies, suggesting that the latter exposure routes may not lead to absorption and toxicity in the internal tissues. Comparison of the effects of injected CNMs with aqueous and dietary CNMs exposures indicates that these materials are of minimal environmentally-relevant toxicity in rainbow trout.

Effects of Pb plus Cd mixtures on toxicity, and internal electrolyte and osmotic balance in the rainbow trout (Oncorhynchus mykiss)

The physiological and toxicological effects of Cd and Pb have been thoroughly studied, but relatively little work has been done to determine how mixtures of these metals affect fishes in soft (<100μmolL−1Ca2+) slightly acidic (pH ∼6) waters typical of many lakes in the Canadian Shield and other regions. Recently, it has been suggested that acute exposure to Cd plus Pb mixtures (3h) had greater than additive effects on both Ca2+ and Na+ influx, which could potentially exacerbate disturbances to ion balance and result in greater toxicity in rainbow trout (Oncorhynchus mykiss). The goal of the present study was to test this hypothesis by assessing the physiological and toxicological effects of Cd plus Pb mixtures over longer time periods (3–5 days), but at relatively low, more environmentally relevant concentrations of these metals. Accordingly, toxicity and measurements of blood acid-base regulation (PaO2, pHa), hematology (Ht, Hb, MCHC, and Protein), ionic composition (body ions and plasma Ca2+, Na+, Cl−, osmolality), unidirectional Na+ fluxes and branchial Na+/K+-ATPase activity were measured in rainbow trout exposed to Cd plus Pb mixtures. Experiments on rainbow trout, implanted with dorsal aortic catheters for repetitive blood sampling, demonstrated that exposure to Pb alone (26nmolPbL−1) was less toxic than Cd alone (6nmolCdL−1), which was much less toxic to the fish than a Cd plus Pb mixture (7nmolCdL−1 plus 45nmolPbL−1), which led to greater than additive 80% mortality by 5d. Both Cd and Pb inhibited Na+ influx over 3d exposure to the metals, which was partially offset by decreases in the diffusive efflux (outflux) of Na+ across the gill. Despite an absence of detectable effects of Pb alone on plasma ion balance, Cd plus Pb mixtures exacerbated Cd-induced reductions in plasma Ca2+ concentration, and resulted in pronounced reductions in plasma Na+, Cl−, and osmolality. No effects on Na+/K+-ATPase activity were noted following exposure to Cd, Pb or Pb plus Cd mixtures. We conclude that the greater than additive toxicity of Cd plus Pb mixtures observed in the present and previous studies is because these metals not only have common, but also independent binding sites and mechanisms of action, which could exacerbate the pathophysiological effects caused by each metal alone.

Comparative proteomics of copper exposure and toxicity in rainbow trout, common carp and gibel carp

Species specific differences in transporters, chaperones, metal binding proteins and other targets are important in metal toxicity. Therefore, we have studied the effects of copper exposure on the proteome of gill tissue from Oncorhynchus mykiss, Cyprinus carpio and Carassius auratus gibelio, which have different sensitivities toward copper. Fish were exposed to the Flemish water quality standard for surface waters, being 50μg/L, for 3days. Sampled gill tissue was subjected to a 2D-Dige and an iTRAQ analysis. While gibel carp showed more positive responses such as increased apolipoprotein A-I, transferrin and heat shock protein 70, common carp's gill tissue on the other hand displayed a changed actin cytoskeleton, and indications of a changed metabolism. These last two traits were evident in rainbow trout as well, together with decreased expressions of transferrin and albumin. urthermore, the Weighted Gene Co-Expression Network Analysis of rainbow trout data revealed a network of 98 proteins related to Cu accumulation in gill, of which the occurrence of proteins related to oxidative stress, such as superoxide dismutase and cytochrome c were promising. Additionally, the outcome of the different proteomics techniques demonstrates the usefulness of iTRAQ analysis compared to 2D-Dige and the need for fully annotated genomes.

Cadmium- and calcium-mediated toxicity in rainbow trout ( Oncorhynchus mykiss) in vivo: Interactions on fitness and mitochondrial endpoints

Rainbow trout were exposed to sublethal waterborne Cd (5 and 10 μg L −1) and dietary Ca (60 mg g −1), individually and in combination, for 30 d to elucidate the interactive effects and evaluate the toxicological significance of mitochondrial responses to these cations in vivo. Indices of fish condition and mortality were measured and livers, centers of metabolic homeostasis, were harvested to assess mitochondrial function and cation accumulation. All indices of condition assessed (body weight, hepatosomatic index and condition factor) were reduced in all the treatment groups. Mortality occurred in the Cd-exposed groups with dietary Ca partly protecting against and enhancing it in the lower and higher Cd exposure, respectively. State 3 mitochondrial respiration was inhibited by 30%, 35% and 40% in livers of fish exposed to Ca, Cd and Cd + Ca, respectively, suggesting reduced ATP turnover and/or impaired substrate oxidation. While the phosphorylation efficiency was unaffected, state 4 and state 4+ (+ oligomycin) respirations were inhibited by all the exposures. Mitochondrial coupling was reduced and transiently restored denoting partially effective compensatory mechanisms to counteract Cd/Ca toxicity. The respiratory dysfunction was associated with accumulation of both Cd and Ca in the mitochondria. Although fish that survived acute effects of Cd and Ca exposure apparently made adjustments to energy generation such that liver mitochondria functioned more efficiently albeit at reduced capacity, reduced fitness was persistent possibly due to increased demands for maintenance and defense against toxicity. Overall, interactions between Cd and Ca on condition indices and mitochondrial responses were competitive or cooperative depending on exposure concentrations and duration.

Evaluation of Antioxidant Circulatory Lipid-Soluble Vitamins and Sodium as Non-invasive Indicators of Chronic Copper Exposure and Toxicity in Rainbow Trout, Oncorhynchus mykiss

Measurement of circulatory indicators of copper (Cu) exposure and toxicity in rainbow trout revealed elevated Cu concurrent with reduced sodium (Na) concentrations in plasma of Cu-exposed fish. Using a new normal phase high performance liquid chromatography (HPLC) method developed and validated for simultaneous extraction of lipid-soluble antioxidant vitamins we found that, contrary to our original hypothesis, plasma antioxidant status was enhanced as evidenced by a linear increase in vitamin E concentration. This suggests that vitamin E was mobilized from other metabolic pools to enhance circulatory antioxidant status possibly for delivery to Cu-sensitive locales. On the other hand, plasma vitamin A was not affected by the Cu exposure although its level decreased with time concurrent with an increase in fish size suggesting increased demand for growth. Thus circulatory Cu, Na, and vitamin E, but not vitamin A, can be used as non-lethal biomarkers of chronic Cu exposure and toxicity in fish.

Radiotracer Studies on Waterborne Copper Uptake, Distribution, and Toxicity in Rainbow Trout and Yellow Perch: A Comparative Analysis

ABSTRACT 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 that 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—that is, a species that inhabits metal-contaminated lakes around northern Canadian industrial operations.

Renal responses to acute lead waterborne exposure in the freshwater rainbow trout ( Oncorhynchus mykiss)

The possible nephrotoxic effects of waterborne lead exposure (as Pb(NO 3) 2) were investigated in the freshwater rainbow trout ( Oncorhynchus mykiss). Kidney lead accumulation was time-dependent, increasing upon exposure to 0.57 ± 0.01 mg dissolved Pb L −1 for up to 96 h with a significantly higher burden occurring in the posterior kidney compared to the anterior segment. Urine analyses in trout exposed to 1.20 ± 0.09 mg dissolved Pb L −1 revealed a significant increase in urinary lead excretion rate throughout 96 h of exposure. Urine flow rate and glomerular filtration rate (GFR) were not impacted with the exception of a significant decrease in GFR from 84 to 96 h in lead-exposed trout. Urine pH decreased significantly over time in lead-exposed fish. Correspondingly, urine ammonia excretion rate showed a marked increase from 48 h onwards. In experimental fish, urine glucose excretion was significantly greater by 96 h while urine lactate, urea and protein excretion were not significantly altered by lead exposure. The urine excretion rate of Ca 2+ increased significantly by approximately 43% after only 24 h of lead exposure, and was maintained at a higher rate than controls for up to 96 h. Magnesium excretion increased in a time-dependent fashion, reaching a two- to three-fold rise by 96 h. In contrast, rates of Na + and Cl − excretion were decreased in experimental fish by approximately 30% by 48 h, this trend continuing for the duration of lead-exposure. There were no changes in any of these parameters in similarly treated control fish. Clearance ratio analyses indicated progressive decreases in the net reabsorption efficiencies of the renal system for Ca 2+, Mg 2+, Pb, and glucose, suggesting that the active tubular transport mechanisms for these substances were inhibited by lead exposure, while Na +, K +, Cl −, lactate, and protein reabsorptions were unaffected. Net ammonia secretion increased. We conclude that changes in renal function both reflect and help to minimize some of the associated disturbances in systemic physiology. Lead-induced ionoregulatory toxicity in rainbow trout, particularly the disturbance of Ca 2+ homeostasis, is not exclusively a branchial phenomenon, but is in part a result of disruption of ionoregulatory mechanisms at the kidney. This action of lead outside the gills is critical to consider when developing guidelines for water quality.