The effects of salinity on acute toxicity of zinc to two euryhaline species of fish, Fundulus heteroclitus and Kryptolebias marmoratus

Time-efficient approach for environmental transformation and bioavailability assessment of isotopically enriched nanoparticles to increase environmental relevance

The increasing use of engineered nanoparticles (NPs) and their release into the environment requires an assessment of their fate and (eco-) toxicological effects. Previous studies have often focused on pristine NPs or NPs spiked into the effluent of simulated wastewater treatment plants (WWTP) fed with artificial wastewater, combined with unrealistic high exposure concentrations to overcome problems associated with high metal background concentrations. In this study environmentally transformed NPs were obtained by direct spiking into an anaerobic digester filled with municipal sewage sludge. Isotopically enriched 46TiO2 and 68ZnONPs were synthesized and used in the study to allow tracing of their fate in WWTP matrices at environmentally relevant concentrations, despite the high Zn and Ti background levels. NP-spiked sludge was used to create exposure media for uptake studies with the benthic amphipod Hyalella azteca under freshwater and brackish conditions. The results show that while 68ZnONPs nearly achieved the target concentration (90 versus 100 mg 68Zn/kg) in the spiked sludge, the 46TiO2NPs reached only 33 % of the target concentration (100 mg 46Ti /kg), despite the good homogeneity of the 46Ti distribution in the spiked sludge. The latter discrepancy most likely reflects aggregation and subsequent sedimentation of the 46TiO2NPs in the digester unit. Exposure of H. azteca to transformed 68ZnONPs at concentrations between 3.5 and 9.7 μg 68Zn/L led to significant 68Zn accumulation in tissues. Our results show that the transformation processes led to an up to 12 times reduced uptake of 68Zn from the transformed as compared to the pristine 68ZnONPs, and this effect was more pronounced at freshwater exposure conditions. The new method of spiking an anaerobic sludge digestion unit balances environmental relevance, costs, time-efficiency and NPs losses (compared to spiking complete WWTP pilot systems or laboratory models) but requires optimization for NPs prone to aggregation such as TiO2NPs.

Effects of salinity on behavior and reproductive toxicity of BPA in adult marine medaka

Salinity is an important environmental factor influencing the toxicity of chemicals. Bisphenol A (BPA) is an environmental endocrine disruptor with adverse effects on aquatic organisms, such as fish. However, the influence of salinity on the biotoxicity of BPA and the underlying mechanism are unclear. In this study, we exposed marine medaka (Oryzias melastigma) to BPA at different salinities (0 psμ, 15 psμ, and 30 psμ) for 70days to investigate the toxic effects. At 0 psμ salinity, BPA had an inhibitory effect on the swimming behavior of female medaka. At 15 psμ salinity, exposure to BPA resulted in necrotic cells in the ovaries but not on the spermatozoa. In addition, BPA exposure changed the transcript levels of genes related to the nervous system (gap43, elavl3, gfap, mbpa, and α-tubulin) and the hypothalamic-pituitary-gonadal (HPG) axis (fshr, lhr, star, arα, cyp11a, cyp17a1, cyp19a, and erα); the expression changes differed among salinity levels. These results suggest that salinity influences the adverse effects of BPA on the nervous system and reproductive system of medaka. These results emphasize the importance of considering the impact of environmental factors when carrying out ecological risk assessment of pollutants.

Antioxidant response to ZnO nanoparticles in juvenile Takifugu obscurus: protective effects of salinity

The extensive utilization of Zinc Oxide nanoparticles (ZnO NPs) has garnered significant attention due to their detrimental impacts on ecosystem. Unfortunately, ecotoxicity of ZnO NPs in coastal waters with fluctuating salinity has been disregarded. This study mainly discussed the toxic effects of ZnO NPs on species inhabiting the transition zones between freshwater and brackish water, who are of great ecological and economic importance among fish. To serve as the model organism, Takifugu obscurus, a juvenile euryhaline fish, was exposed to different ZnO NPs concentrations (0-200 mg/L) and salinity levels (0 and 15 ppt). The results showed that a moderate increase in salinity (15 ppt) could alleviate the toxic effect of ZnO NPs, as evidenced by improved survival rates. The integrated biomarker response index on oxidative stress also revealed that the toxicity of ZnO NPs was higher in freshwater compared to brackish water. These outcomes can be attributed to higher salinity (15 ppt) reducing the bioavailability of ZnO NPs by facilitating their aggregation and inhibiting the release of metal ions. It is noteworthy that elevated salinity was found to alleviate ZnO NPs toxicity by means of osmotic adjustment via the activation of Na+/K+-ATPase activity. This study demonstrates the salinity-dependent effect of ZnO NPs on T. obscurus, suggesting the possibility for euryhaline fish like T. obscurus to adapt their habitat towards more saline environments, under constant exposure to ZnO NPs.

Tissue metal concentrations and antioxidant enzyme activity in western north Atlantic white sharks (Carcharodon carcharias)

Anthropogenic practices have increased metal contamination in marine ecosystems. Most sharks have long lifespans, occupy an important ecological position at the top of marine food webs, and can accumulate metals. However, reference levels of metal contaminants in the tissues of sharks, particularly, apex predators such as the white shark (Carcharodon carcharias), are lacking. In this study, concentrations of copper (Cu), cadmium (Cd), nickel (Ni), lead (Pb), silver (Ag), and zinc (Zn) were measured in the muscle tissue of white (n = 42) and tiger (Galeocerdo cuvier; n = 3) sharks. Metal exposure in various species, including sharks, has been correlated with increased oxidative stress. Therefore, the main objectives of this study were to assess metal accumulation and antioxidant enzyme activity (superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx)) in the muscle tissue of the population of white sharks and tiger sharks inhabiting the Western North Atlantic. The measured parameters were qualitatively compared between species. The small sample size of tiger sharks (collected from only one site) limited statistical analyses, therefore, white sharks were the primary focus of this study. Differences in tissue metal (Cu, Cd, Ni, and Zn) concentrations and antioxidant enzyme activities were detected based on collection site, with significant positive correlations between Cd and enzymes, SOD and CAT, and Zn and enzymes, SOD and GPx in C. carcharias. Differences in Ni concentration were detected based on sex, with females having higher Ni levels. Additionally, plasma osmolality was not correlated with tissue metal concentrations; however, osmolality decreased with increasing length in C. carcharias. This study is the first to report baseline levels of Cu, Zn, Cd, Ni, Ag, and Pb in muscle of North Atlantic white sharks and provides new insights into oxidative stress responses of these sensitive species to metal contaminants.

Applying Generic Water Quality Criteria to Cu and Zn in a Dynamic Aquatic Environment—The Case of the Brackish Water Formation Strömmen-Saltsjön

The EU Water Framework Directive stipulates that all EU waterways shall have good chemical and ecological status by 2027. Methodologies are described for how to assess and classify waterbodies and make 7-year management plans. Aquatic risk assessment methodologies and environmental quality standards are defined and a biotic ligand model methodology is available to assess the influence of water chemistry on the ability of aquatic organisms to take up metals. Aquatic status classification practices of naturally occurring river basin-specific metals are discussed, specifically how Cu and Zn water quality criteria guideline values have been adopted and defined for Swedish coastal and estuarine waters and how well they represent possible ecological risks. Calculations of bioavailability and ecotoxicity are conducted using recognised models for the Strömmen-Saltsjön water body in Stockholm, in which naturally occurring metals, especially Cu, have among the highest background concentrations of Sweden. Proposals are made to improve risk assessment methodologies to better reflect the vitality of living organisms, and to what extent current levels of these metals in Swedish waterways may influence their welfare. The study concludes that a more local assessment including, e.g., studies of the benthic fauna would be relevant for ecological status classification.

Influence of salinity on the toxicity of copper and cadmium to Zebrafish embryos

Salinization has become a serious worldwide environmental perturbation in freshwater ecosystems. Concomitantly, many of such ecosystems are already impacted by other toxicants, which together with increased salinity may result in synergistic, antagonistic or additive toxic effects to biota. This work intended to assess the influence of increasing salinity (by using NaCl) on the lethal and sublethal toxicity of two metallic elements (copper and cadmium) in embryos of the fish species Danio rerio. This goal was achieved by exposing zebrafish embryos to seven concentrations of NaCl, individually or combined with each metal, using a full factorial design. The following endpoints were monitored in the test organisms: mortality, hatching, malformations and the enzymatic activity of glutathione S-transferase (GST) and cholinesterase (ChE). Overall, moderate salinity levels alleviated the lethal toxicity of both copper and cadmium although this effect was stronger in the copper assay. This effect was also influenced, as expected, by the concentrations of the metals indicating that the protective effect of salt only reaches some levels, after what is overwhelmed by the high metal toxicity, especially with the non-essential metal cadmium. At sub-lethal concentrations, the interactive effect resulting from NaCl and metals was not consistent and varied with the endpoint analyzed and the metal tested. Overall, the interactions between the salt and metals seem complex and with more drastic effects (positive or negative) on lethal endpoints than sub-lethal.

Nutrition and Metabolism of Minerals in Fish

Simple Summary

Our aim is to introduce the mineral nutrition of fish and explain the complexity of determining requirements for these elements, which are absorbed and excreted by the fish into the surrounding water. To date, only the requirements for nine minerals have been investigated. The review is focused on the absorption and the dietary factors that reduce their absorption from feed ingredients of plant and animal origin. Some diseases, such as cataracts, anemia and bone deformity, have been linked to dietary deficiency of minerals.

Abstract

Aquatic animals have unique physiological mechanisms to absorb and retain minerals from their diets and water. Research and development in the area of mineral nutrition of farmed fish and crustaceans have been relatively slow and major gaps exist in the knowledge of trace element requirements, physiological functions and bioavailability from feed ingredients. Quantitative dietary requirements have been reported for three macroelements (calcium, phosphorus and magnesium) and six trace minerals (zinc, iron, copper, manganese, iodine and selenium) for selected fish species. Mineral deficiency signs in fish include reduced bone mineralization, anorexia, lens cataracts (zinc), skeletal deformities (phosphorus, magnesium, zinc), fin erosion (copper, zinc), nephrocalcinosis (magnesium deficiency, selenium toxicity), thyroid hyperplasia (iodine), muscular dystrophy (selenium) and hypochromic microcytic anemia (iron). An excessive intake of minerals from either diet or gill uptake causes toxicity and therefore a fine balance between mineral deficiency and toxicity is vital for aquatic organisms to maintain their homeostasis, either through increased absorption or excretion. Release of minerals from uneaten or undigested feed and from urinary excretion can cause eutrophication of natural waters, which requires additional consideration in feed formulation. The current knowledge in mineral nutrition of fish is briefly reviewed.

Synthesis and characterization of zinc-hexacyanoferrate composite beads for controlling the ammonia concentration in low-temperature live seafood transports

A new water treatment technology is presented for extending the longevity and increasing the maximal bio-load of container-bound, lucrative live seafood transportations. The technology is designed for removing ammonia and minimizing the bacterial concentration that develop in the water during the transport. This paper focuses on the characteristics of self-synthesized polyether-sulfone (PES) coated Zn-HCF composite beads, which have a high adsorbing capacity for NH₄⁺ in seawater and constitute the heart of the developed technology. Adsorption isotherms show that the operational capacity of the composite material (PES = 20% w/w) at NH₄⁺ concentration of 10 mgN/L at 3.5 °C is ∼3 mgN/g Zn-HCF. The kinetics of the PES-coated beads were shown to be considerably slower than the bare Zn-HCF, but since the retention time in the transport is long (many days), this does not detract from the effectiveness of the adsorption. Simulation experiments with and without live fish showed that the adsorbing material behaved as expected during a 21-d trip and that it did not have any effect on the fish. Repeated adsorption/regeneration (3 and 6 M NaCl) tests proved the composite material's stability and ion-exchange robustness. Electrooxidation of the ammonia in the exhausted regeneration solution was carried out with high efficiency and the treated solution could be used effectively in the following chemical regeneration step. The cost of a treatment unit installed in a 40-foot container was estimated at $40,000 and the ROI at 6 to 12 months.

Influence of salinity on physiological development and zinc toxicity in the marine medaka Oryzias melastigma

To determine whether the marine medaka Oryzias melastigma is a suitable model organism for evaluating the effects of environmental chemicals on marine teleosts, we examined the effect of salinity on physiological development and zinc toxicity. Growth as measured by total body length was significantly lower in fresh water compared to brackish water. Reproductive success was also significantly reduced in fresh water, although we observed cells in the pituitary producing gonadotropins such as Gpa (common glycoprotein hormone α), Fshb (follicle stimulating hormone β), and Lhb (luteinizing hormone β) at all salinities. These results indicate that O. melastigma is adaptable to various salinities from fresh to seawater, and brackish water is best for physiological processes including growth performance and reproduction. When zinc was dissolved in saltwater, a white precipitate formed immediately, and the dissolved concentration decreased in the supernatant and increased at precipitate. We performed zinc toxicity tests on early life stage and adult stage in fresh water, brackish water, and seawater. Among adults, the lowest observed effect concentration for mortality in freshwater (15.3 mg/L) was lower than in brackish water (>48 mg/L) or seawater (>48 mg/L). Similarly, among embryos and larvae, the lowest observed effect concentration for mortality in freshwater (4.8 mg/L) was lower than in brackish water (48 mg/L) or seawater (48 mg/L). These results highlight the importance of using marine organisms to evaluate the ecological effects of marine pollutants.

Brazilian silverside, Atherinella brasiliensis (Quoy & Gaimard,1825) embryos as a test-species for marine fish ecotoxicological tests

The fish embryo test (FET) is an alternative to the classic freshwater toxicity test used to assess environmental hazards and risks to fish. This test has been standardized and adopted by the Organization for Economic and Cooperation and Development (OECD). As salinity may affect the substances’ toxicity, we describe the development of an alternative euryhaline test species for embryonic ecotoxicological tests: the Brazilian silverside Atherinella brasiliensis (Quoy & Gaimard, 1825). This species is broadly distributed along the coast of South America and is able to inhabit a broad range of environmental and saline conditions. Ours is the first study on the maintenance of a native South American species for natural reproduction and the generation of embryos for tests. The embryos used are transparent and possess fluorescent cells which have only been seen in a few species and which may be used as markers, making it an alternative assessment tool for the lethal and sublethal substances in marine and estuarine environments. We provide a detailed description and analysis of embryonic development under different salinities and temperatures. The embryos and larvae developed in similar ways at different salinities, however as temperatures increased, mortality also increased. We considered the effects of the reference toxicants Zn²⁺ and SDS using a protocol similar to the FET that was standardized for zebrafish. Brazilian silverside embryos are as sensitive as freshwater, or euryhaline fish, to the surfactant but are more resistant to metals prior to hatching. We were able to show the advantages of the Brazilian silverside as a model for a marine fish embryo test (FETm) with high levels of reproducibility and little contaminated waste.

Role of metal speciation in the exposure medium on the toxicity, bioavailability and bio-reactivity of copper, silver, cadmium and zinc in the rainbow trout gut cell line (RTgutGC)

The role of metal speciation on metal bioavailability, bio-reactivity and toxicity at the fish intestine is poorly understood. To investigate these processes, we used an in vitro model of the rainbow trout (Oncorhynchus mykiss) intestine, the RTgutGC cell line. Cells were exposed to two essential metals (copper and zinc) and two non-essential metals (cadmium and silver) in a medium of well-defined composition, which allowed the determination of metal speciation in solution. Concentrations resulting in a 50% cell viability reduction (EC₅₀) were measured using a viability assay based on two endpoints: metabolic activity and membrane integrity. Metal bioavailability and bio-reactivity was studied at non-toxic (300 nM all metals) and toxic (EC₁₀; Ag-0.6, Cu-0.9, Cd-3, and Zn-9 μM) concentrations. Bioavailability (i.e. intracellular metal accumulation) was determined by ICP-MS, while bio-reactivity (i.e. induction of a metal specific transcriptional response) was determined by measuring the mRNA levels of a known biomarker of metal exposure (i.e. metallothionein) and of copper and zinc transporters (i.e. ATP7A and ZnT1). Dominant metal species in the exposure medium were Zn²⁺, CuHPO₄, CdCl⁺, and AgCl₂^- respectively for Zn, Cu, Cd, and Ag. The EC_50s showed the metal toxicity hierarchy: Ag > Cu > Cd > Zn. In RTgutGC cells, essential metal homeostasis was tightly regulated while non-essential metals accumulated more readily. Non-essential metals were also more bio-reactive inducing higher MT and ZnT1 mRNA levels. Taken together these findings indicate that metal toxicity in RTgutGC cannot solely be explained by extracellular metal speciation but requires the evaluation of metal bioavailability and bio-reactivity.

Characterization of alloying components in galvanic anodes as potential environmental tracers for heavy metal emissions from offshore wind structures

The impact of offshore constructions on the marine environment is unknown in many aspects. The application of Al- and Zn-based galvanic anodes as corrosion protection results in the continuous emission of inorganic matter (e.g. >80 kg Al-anode material per monopile foundation and year) into the marine environment. To identify tracers for emissions from offshore wind structures, anode materials (Al-based and Zn-based) were characterized for their elemental and isotopic composition. An acid digestion and analysis method for Al and Zn alloys was adapted and validated using the alloy CRMs ERM®-EB317 (AlZn6CuMgZr) and ERM®-EB602 (ZnAl4Cu1). Digests were measured for their elemental composition by ICP-MS/MS and for their Pb isotope ratios by MC ICP-MS. Ga and In were identified as potential tracers. Moreover, a combined tracer approach of the elements Al, Zn, Ga, Cd, In and Pb together with Pb isotope ratios is suggested for a reliable identification of offshore-wind-farm-induced emissions. In the Al anodes, the mass fractions were found to be >94.4% of Al, >26200 mg kg^-1 of Zn, >78.5 mg kg^-1 of Ga, >0.255 mg kg^-1 of Cd, >143 mg kg^-1 of In and >6.7 mg kg^-1 of Pb. The Zn anodes showed mass fractions of >2160 mg kg^-1 of Al, >94.5% of Zn, >1.31 mg kg^-1 of Ga, >254 mg kg^-1 of Cd, >0.019 mg kg^-1 of In and >14.1 mg kg^-1 of Pb. The n(²⁰⁸Pb)/n(²⁰⁶Pb) isotope ratios in Al anodes range from 2.0619 to 2.0723, whereas Zn anodes feature n(²⁰⁸Pb)/n(²⁰⁶Pb) isotope ratios ranging from 2.0927 to 2.1263.

Effect of salinity on zinc toxicity (ZnCl2 and ZnO nanomaterials) in the mosquitofish (Gambusia sexradiata)

Zn is an essential trace metal in living beings. However, excessive concentrations can cause toxic effects even in the aquatic biota. Zn is widely used in different industrial sectors, which has increased its presence in aquatic environments. To assess the acute toxicity of Zn, bioassays were performed with the fish Gambusia sexradiata for a 96-h exposure using ZnCl₂ (0 and 15 salinity) and ZnO nanomaterials (0 salinity). The mean lethal concentrations (LC₅₀-96 h) for ZnCl₂ were 25.36 (19.64-32.76) and 177.91 (129.39-244.63) mg Zn L^-1 to 0 and 15 salinity, respectively. The increased concentration of ZnCl₂ showed a dose-response relationship; similarly, the increase in salinity significantly reduces the toxicity of Zn. Characterisation of ZnO nanomaterials was carried out by FTIR, DRX, SEM, DLS and zeta potential. The FTIR spectra showed the characteristic band of Zn-O vibration at 364 cm^-1, while DRX presents the hexagonal wurtzite structure with an average crystallite size of 40 nm. SEM micrographs reveal rod-like shapes with lengths and diameters of 40-350 nm and 90 nm, respectively. Agglomerates of 423 nm in water suspension were obtained by DLS and zeta potential of + 14.4 mV. Under these conditions, no mortality was observed due to the rapid flocculation/precipitation of ZnO nanomaterials, which involved brief interaction periods of Zn in the water column with the fish. Gambusia sexradiata is affected by increased Zn concentrations in hard water conditions, and salinity changes modified Zn toxicity, placing it as a suitable model for toxicity tests for this type of particles.

Choice consequences: salinity preferences and hatchling survival in the mangrove rivulus (Kryptolebias marmoratus)

In heterogeneous environments, mobile species should occupy habitats in which their fitness is maximized. Mangrove rivulus fish inhabit mangrove ecosystems where salinities range from 0 to 65 ppt, but are most often collected from areas with salinities of ∼25 ppt. We examined the salinity preference of mangrove rivulus in a lateral salinity gradient, in the absence of predators and competitors. Fish could swim freely for 8 h throughout the gradient with chambers containing salinities ranging from 5 to 45 ppt (or 25 ppt throughout in the control). We defined preference as the salinity in which the fish spent most of their time, and also measured preference strength, latency to begin exploring the arena, and number of transitions between chambers. To determine whether these traits were repeatable, each fish experienced three trials. Mangrove rivulus spent a greater proportion of time in salinities lower (5-15 ppt) than they occupy in the wild. Significant among-individual variation in the (multivariate) behavioral phenotype emerged when animals experienced the gradient, indicating strong potential for selection to drive behavioral evolution in areas with diverse salinity microhabitats. We also showed that mangrove rivulus had a significantly greater probability of laying eggs in low salinities compared with control or high salinities. Eggs laid in lower salinities also had higher hatching success compared with those laid in higher salinities. Thus, although mangrove rivulus can tolerate a wide range of salinities, they prefer low salinities. These results raise questions about factors that prevent mangrove rivulus from occupying lower salinities in the wild, whether higher salinities impose energetic costs, and whether fitness changes as a function of salinity.

The influence of salinity and water chemistry on acute toxicity of cadmium to two euryhaline fish species

The euryhaline killifishes, Fundulus heteroclitus and Kryptolebias marmoratus inhabit estuaries that rapidly change salinity. Although cadmium (Cd) toxicity has been well characterized in fish inhabiting freshwaters, fewer studies have examined the toxic effects of Cd in estuarine and saltwater environments. Additionally, current environmental regulations do not account for organism physiology in different salinity waters even though metal sensitivity is likely to change in these environments. In this study, we investigated effects of changing salinity on acute Cd toxicity to larval (7-9 d old) F. heteroclitus and K. marmoratus. Median 96-h lethal concentrations (LC50) for Cd were calculated for both fish species at six different salinities. As salinity increased, metal toxicity decreased in both fish species up to 18 ppt salinity; and F. heteroclitus were more sensitive than K. marmoratus at salinities above 12 ppt. To determine which components of saltwater were protective against Cd toxicity, we investigated the influence of CaSO₄ (100 and 200 mg/L), CaCl₂ (200 mg/L), and MgSO₄ (300 mg/L) on Cd toxicity to K. marmoratus. The results demonstrated that both competition with calcium and complexation with chloride reduced the toxic effects of Cd to K. marmoratus. These findings could be used to improve marine/estuarine biotic ligand models for the determination of site-specific water quality criteria for Cd.

Zinc nanoparticles potentiates thermal tolerance and cellular stress protection of Pangasius hypophthalmus reared under multiple stressors

A preliminary study was conducted to delineate the ameliorating effect of dietary zinc nanoparticles (Zn-NPs) against thermal stress in Pangasius hypophthalmus reared under concurrent exposure to lead (Pb) and elevated temperature (34°C). Three diets were formulated such as control (no Zn-NPs), Zn-NPs 10 and 20mg/kg diet. Two hundred and thirty four fish were randomly distributed in to six treatments groups in triplicates; such as control group (no Zn-NPs in diet and unexposed to Pb and temperature, Ctr/Ctr), control diet with concurrent exposure to Pb and temperature (Pb-T/Ctr), Zn-NPs 10 and 20mg/kg without stressors (Zn-NPs 10mg/kg, Zn-NPs 20mg/kg), Zn-NPs 10 and 20mg/kg diet with concurrent exposure to Pb and temperature (Pb-T/Zn-NPs 10mg/kg, Pb-T/Zn-NPs 20mg/kg). The Pb in treated water was maintained at the level of 1/21th of LC₅₀ (4ppm) at 34 °C temperature in stressors groups. Post 60 days feeding trial, critical thermal minimum (CTmin), lethal thermal minimum (LTmin), and critical thermal maximum (CTmax), lethal thermal maximum (LTmax) and biochemical attributes on P. hypophthalmus were evaluated. The results indicated that, dietary supplementation of Zn-NPs increased the CTmin, LTmin and CTmax, LTmax in P. hypophthalmus. Positive correlations were observed between CTmin LTmin (Y = - 0.495 + 10.08x, R², 0.896) and CTmax LTmax (Y = - 0.872 + 4.43x, R², 0.940). At the end of the thermal tolerance study, oxidative stress and lipid peroxidation (LPO) were significantly reduced and neurotransmitter enzyme was significantly increased in the groups fed with Zn-NPs @ 10mg and 20mg/kg diet. Overall results indicated that dietary Zn-NPs can confer protection against thermal stress in P. hypophthalmus.

Dietary zinc promotes immuno-biochemical plasticity and protects fish against multiple stresses

The abiotic and biotic stress is an episode that effect on regulatory, neuro-endocrine and immune systems of animals including fish. The stress creates stimulatory and suppressive of immune system resulting in increases the incidence of infection. In view of these points, we have conducted an experiment to mitigate the stress through a nutritional approach through Zinc (Zn) supplementation in Pangasius hypophthalmus (initial weight-3.65 ± 0.75 g). Three isocaloric and isonitrogenous diets with graded levels of zinc 0, 10 and 20 mg/kg were prepared and fed to seven different groups with each in triplicate. The experimental group as follows as normal water with control diet (Ctr/Ctr), lead (Pb) exposed and fed with control diet (Ctr/Pb), control diet and exposed to Pb and temperature (Ctr/Pb-T), Zn 10 mg/kg fed without stressors (Zn- 10 mg/kg), Zn 20 mg/kg fed without stressors (Zn-20 mg/kg), Zn 10 mg/kg fed and Pb and temperature exposed (Pb-T/Zn 10 mg/kg) and Zn 20 mg/kg fed and exposed to Pb and temperature (Pb-T/Zn 20 mg/kg). The Pb in treated water was maintained at the level of 1/20th of LC₅₀ (4 ppm) and temperature at 34 ^°C in exposure groups. The neutraceuticals role of dietary Zn was studied in terms of antioxidative enzymes (catalase, superoxide dismutase, glutathione-S-transferase), stress markers (Heat shock protein 70, cortisol, acetylcholine esterase, blood glucose, Vitamin C), immunological parameters (Total protein, albumin, globulin, A/G ratio and NBT) and subsequent challenge with Aeromonas veronii biovar sobria. The antioxidative enzymes, stress markers, albumin were significantly (p < 0.01) elevated, brain AChE and immuno-hematological parameters were significantly (p < 0.01) decreased due to lead (Pb) and temperature exposure. The relative survival (%) was reduced due to the concurrent effect of Pb, high temperature stress and bacterial challenge. Zinc at the rate of 10 and 20 mg/kg was found to be restore the biochemical and immunological parameters against concurrent exposure to lead (Pb), temperature and pathogenic infection. Results obtained in the present study indicate that supplementation of 10 and 20 mg/kg of Zn in the diet has a definitive role in the mitigation of lead (Pb) and temperature exposure along with pathogenic infection in P. hypophthalmus.

Derivation of marine water quality criteria for metals based on a novel QICAR-SSD model

Establishment of water quality criteria (WQC) is one procedure for protection of marine organisms and their ecosystems. This study, which integrated two separate approaches, quantitative ion character-activity relationships (QICARs) and species sensitivity distributions (SSDs), developed a novel QICAR-SSD model. The QICARs predict relative potencies of individual elements while SSDs integrate relative sensitivities among organisms. The QICAR-SSD approach was applied to derive saltwater WQC for 34 metals or metalloids. Relationships between physicochemical properties of metal ions and their corresponding potencies for acute toxicity to eight selected marine species were determined. The softness index (σp) exhibited the strongest correlation with the acute toxicity of metals (r (2) > 0.66, F > 5.88, P < 0.94 × 10(-2)). Predictive criteria maximum concentrations for the eight metals, derived by applying the SSD approach to values predicted by use of QICARs, were within the same order of magnitude as values recommended by the US EPA (2009). In general, the results support that the QICAR-SSD approach is a rapid method to estimate WQC for metals for which little or no information is available for marine organisms.

Zinc bioaccumulation and ionoregulatory impacts in Fundulus heteroclitus exposed to sublethal waterborne zinc at different salinities

Exposure of Fundulus heteroclitus to an environmentally relevant Zn concentration (500 μg L⁻¹) at different salinities (0, 3.5, 10.5, and 35 ppt) revealed the following effects: (i) plasma [Zn] doubled after exposure at 0 ppt, a response which was eliminated at 35 ppt. Tissue [Zn] also increased in gill, liver, intestine, and carcass at 0 ppt. (ii) Both branchial and intestinal Ca2⁺ ATPase activities decreased in response to Zn at 0 ppt and were elevated at 35 ppt. Plasma [Ca] decreased by 50% at 0 ppt and by 30% at 3.5 ppt and increased by 20% at 35 ppt. Gill [Ca] decreased by 35% at 0 ppt and increased by about 30% at all higher salinities. (iii) Branchial Na⁺,K⁺ ATPase activity decreased by 50% at 0 ppt, increased by 30% and 90% at 10.5 and 35 ppt respectively. Intestinal Na⁺,K⁺ ATPase activity was reduced by 30% at 0 ppt. (iv) Plasma [Na] decreased by 30% at 0 ppt in Zn-exposed. Zn exposure also disturbed the homeostasis of tissue cations (Na⁺, K⁺, Ca⁺⁺, Mg⁺⁺) in a tissue-specific and salinity-dependent manner. (v) Drinking rate was not altered by Zn exposure. In toxicity tests, acute Zn lethality (96-h LC50) increased in a close to linear fashion from 9.8 mg L⁻¹ at 0 ppt to 75.0 mg L⁻¹ at 35 ppt. We conclude that sublethal Zn exposure causes pathological changes in both Ca⁺⁺ and Na⁺ homeostases, and that increasing salinity exerts protective effects against both sublethal and lethal Zn toxicities.

Sublethal effects of CuO nanoparticles on Mozambique tilapia (Oreochromis mossambicus) are modulated by environmental salinity

The increasing use of manufactured nanoparticles (NP) in different applications has triggered the need to understand their putative ecotoxicological effects in the environment. Copper oxide nanoparticles (CuO NP) are toxic, and induce oxidative stress and other pathophysiological conditions. The unique properties of NP can change depending on the characteristics of the media they are suspended in, altering the impact on their toxicity to aquatic organisms in different environments. Here, Mozambique tilapia (O. mossambicus) were exposed to flame synthesized CuO NP (0.5 and 5 mg·L⁻¹) in two environmental contexts: (a) constant freshwater (FW) and (b) stepwise increase in environmental salinity (SW). Sublethal effects of CuO NP were monitored and used to dermine exposure endpoints. Fish exposed to 5 mg·L⁻¹ CuO in SW showed an opercular ventilation rate increase, whereas fish exposed to 5 mg·L⁻¹ in FW showed a milder response. Different effects of CuO NP on antioxidant enzyme activities, accumulation of transcripts for metal-responsive genes, GSH∶GSSG ratio, and Cu content in fish gill and liver also demonstrate that additive osmotic stress modulates CuO NP toxicity. We conclude that the toxicity of CuO NP depends on the particular environmental context and that salinity is an important factor for modulating NP toxicity in fish.

The influence of salinity on acute nickel toxicity to the two euryhaline fish species, Fundulus heteroclitus and Kryptolebias marmoratus

Nickel (Ni) is a common pollutant found in aquatic environments and may be harmful at elevated concentrations. Increasing salinity has been shown to decrease the bioavailability and toxicity of other metals to aquatic organisms. In the present study, acute Ni toxicity experiments (96-h) were conducted at various salinities (0-36 ppt) to determine the effects of salinity on Ni toxicity to 2 euryhaline fish species, Kryptolebias marmoratus and Fundulus heteroclitus. Nickel concentrations causing lethality to 50% of the fish ranged from 2 mg/L in moderately hard freshwater to 66.6 mg/L in 36 ppt saltwater. Nickel toxicity to F. heteroclitus decreased linearly with increasing salinity; however, Ni toxicity to K. marmoratus was only lowered by salinities above 6 ppt, demonstrating potential physiological differences between the 2 species when they are functioning as freshwater fish. Furthermore, the authors investigated the influence of Mg(2+) , Ca(2+) , Na(+) , and Cl(-) on Ni toxicity to F. heteroclitus. Freshwater with up to 120 mg/L Ca(2+) as CaSO4 , 250 mg/L Mg(2+) as MgSO4 , or 250 mg/L Na(+) as NaHCO3 did not provide protection against Ni toxicity. Alternatively, 250 mg/L Na(+) , as NaCl, was protective against Ni toxicity; and the extent of protection was similar to that demonstrated from salt water with the same Cl(-) concentration. These results suggest that Cl(-) is the predominant ion responsible for reducing Ni toxicity to K. marmoratus and F. heteroclitus in higher salinity waters.

Zinc distribution in the organs of adult Fundulus heteroclitus after waterborne zinc exposure in freshwater and saltwater

Zinc (Zn) is an essential micronutrient to aquatic organisms, but increased concentrations may result in accumulation and toxic effects. Water chemistry is known to influence the uptake of Zn in aquatic biota; therefore, organisms inhabiting environments with variable salinities may exhibit different patterns of Zn accumulation. Likewise, metal uptake can vary in fish as a consequence of ionoregulatory status (acclimated to freshwater or saltwater). The euryhaline fish, Fundulus heteroclitus, was exposed to a control and two increased Zn concentrations (15 and 75 μg/L in moderately hard freshwater and 100 and 1,000 μg/L in 35 g/L saltwater) for 7 days. The ionic Zn concentrations were equivalent in the 75 μg/L Zn treatment in freshwater and the 100 μg/L Zn treatment in saltwater. Throughout the 7-day experiments, fish were dissected, and organ Zn distribution was quantified in the gill, intestine, liver, gall bladder, heart, and carcass. Different patterns of Zn accumulation were observed in F. heteroclitus dependent on exposure medium. Despite lower exposure concentrations, F. heteroclitus accumulated more Zn in freshwater than in saltwater in all of the organs analyzed with the exception of the carcass. In addition, there were correlations between Zn distribution and known physiological mechanisms related to osmoregulation in F. heteroclitus. Furthermore, this research suggests that F. heteroclitus are more susceptible to Zn accumulation in freshwater environments.

"Mangrove 'killifish': an exemplar of integrative biology": introduction to the symposium

The mangrove rivulus, Kryptolebias marmoratus, (hereafter, rivulus) is one of the only two vertebrates known to self-fertilize, with the other being a recently named close relative, Kryptolebias hermaphroditus (Tatarenkov et al. 2012). Rivulus is also the first fish species found to have environmental sex determination, whereby lower temperatures inhibit ovarian development, thus providing one potential route that avoids inbreeding depression (Harrington 1967; Conover 2004). Wild rivulus exist as androdioecious populations in which both hermaphrodites and, although relatively rare, males are found (Taylor 2000). In the laboratory, individual adult rivulus can produce isogenic embryos. Under as yet unknown environmental conditions, males develop and outcrossing between the hermaphrodites and males occurs (Taylor 2000; Mackiewicz et al. 2006a, 2006b). It is intriguing to consider the behavioral, neurological, and endocrinological control necessary to accommodate this reproductive strategy (Sakakura et al. 2006; Orlando et al. 2006; Earley et al. 2008). In addition to environmental sex determination and androdioecious reproduction, rivulus is also known to emerge from its aquatic surroundings and assume a transitory, terrestrial existence (Ong et al. 2007; Taylor et al. 2008; Cooper et al. 2012). Rivulus is an emerging and potentially powerful model for integrative and comparative biological research and, in part, this emergence has been catalyzed by this first symposium on its biology. The well-attended symposium comprised 11 speakers, which included four women and seven men, with academic ranks ranging from postdoctoral fellow to full professor, who came from four countries. This symposium will help drive future research within this taxon and will facilitate collaborations among researchers. It has already facilitated networking between heads of laboratories and current and potential future postdoctoral fellows and students. The organizing committee looks forward to the next rivulus symposium with great anticipation.