Mechanisms of zinc toxicity in the galaxiid fish, Galaxias maculatus

Dietary zinc requirement of juvenile stinging catfish Heteropneustes fossilis based on growth performance, haematology, and tissue mineral composition

This investigation was done to determine how much zinc (Zn) the stinging catfish, Heteropneustes fossilis, needs in its diet. Five isonitrogenous (34.5% protein) and isolipidic (6.0% lipid) diets were prepared to contain graded levels of Zn (0, 10, 20, 30, and 40 mg kg-1), supplied as zinc sulfate (ZnSO4·7H2O), and referred to as Zn0, Zn10, Zn20, Zn30, and Zn40, respectively. A total of 600 fish (initial body weight: 1.41 ± 0.02 g) were stocked in 15 glass aquaria (40 fish/aquarium), each with 180 L water capacity. For ten weeks, each diet was hand fed to three groups of fish twice daily until they appeared satisfied. The highest weight gain and specific growth rate, and lowest feed conversion ratio were recorded in fish fed with a 30 mg Zn kg-1 diet. Zn contents in bone and muscle linearly increased up to 30 mg kg-1 Zn and then remained stable, while iron (Fe) and copper (Cu) contents in bone and muscle had an inverse pattern with the inclusion level of dietary Zn. Increasing dietary Zn levels up to 30 mg kg-1 was found to improve values of hematological parameters such as red blood cell (RBC), white blood cell (WBC), haemoglobin (Hb), and haematocrit (HCT). These values, however, decreased when the dietary Zn level was further increased. The serum alkaline phosphatase level was the highest in fish fed a diet containing 30 mg kg-1 of Zn. Regression analyses based on weight gain, specific growth rate, and bone and muscle Zn concentrations indicated that the optimum dietary Zn requirement for stinging catfish was in a range of 27.4-36.5 mg kg-1.

Differential accumulation of metals in the lacustrine and fluvial Alpine bullheads (Cottus poecilopus) and recovery of fish from metal contamination after a flash flood

The spatiotemporal distribution and transport of mercury, zinc, molybdenum, rubidium, and strontium from alpine terrestrial ecosystems to alpine lake and mountain stream populations of Cottus poecilopus were investigated. Metals were measured for 66 wild fish collected from different lakes and Javorinka stream across. Mercury was measured in the pectoral fins, other elements in the skull. Bullheads contained more metals in the alpine lakes than in the mountain stream. In particular, mercury and zinc concentrations in lake bullheads were 6 and 2.5 times higher, respectively, than those of stream-dwelling fish. New data were generated on metal bioaccumulation in fish of understudied West Carpathian alpine lake environments. In July 2018, a major flood occurred in the area of the Javorinka. Already then, the mercury content in bullheads increased significantly. Bioaccumulation of mercury in fish occurred very quickly after the flood and was also significant in the following 2019. Then, the concentrations of mercury quickly decreased up to 70% in 2021-2022. Average concentrations of molybdenum and rubidium in bullheads in the stream rapidly declined in the year following the flood disturbance, but within less than 2 years, the metal levels stabilized at about the same level as in 2017 prior the flood. Strontium concentrations in fish dropped rapidly immediately after the flood, increased in the following years, and dropped again after 4 years, suggesting that many more factors are influencing strontium bioaccumulation in fish that are comparable in magnitude to the flood. The most serious warning seems to be the absence of biogenic zinc. The average concentration in the Alpine bullheads population in the stream has declined by 70% in less than 5 years and is steadily declining. An important result of this study is the demonstration that disturbance by a single factor (heavy rainfall and flooding) has a clear and timely effect on average metal concentrations in the fish population.

The Reproductive Biology of Puye (Galaxias maculatus) under Experimental Culture

This study determines the reproductive patterns of puye (Galaxias maculatus) under culture conditions. A population of 567 wild fish was caught in the Cautín River, Chile, and held in captivity for four years. Mortality, sex ratio, gonadosomatic index (GSI), sexual maturity stages, spawning period, type and frequency of spawning, and fecundity were measured. The fish grew throughout the experimental period, with the fastest rate during the first half of the first year of life. The highest mortality occurred during the first three months of the experiment and during the spawning season. The sex ratio was almost 1:1 (female:male). First sexual maturity was reached at one year of age, with an average weight of 0.85 ± 0.01 g, total length of 4.85 ± 0.16 cm, and condition factor 0.0074. The highest GSI in both females (12.14 ± 0.74) and males (17.7 ± 2.70) was recorded in August. Nevertheless, the females spawned 3 to 10 times between September and February, with the highest reproductive peak between September and October. The number of embryos per female per day varied from 1 to 429, while the total number of embryos per female during the entire season evaluated varied from 163 to 1044. There was a high correlation (r = 0.82) between absolute fecundity and body weight. Although further studies are needed in this field, these results are basic for establishing future reproductive programs in captivity as a strategy for sustainable fisheries and aquaculture management.

Role of the luminal composition on intestinal metal toxicity, bioavailability and bioreactivity: An in vitro approach based on the cell line RTgutGC

The bioavailability of metal complexes is poorly understood. To evaluate bioavailability and toxicity of neutral and charged complexes as well as free metal ions, Visual Minteq, a chemical equilibrium model, was used to design media containing different metal species. Two non-essential (silver and cadmium) and two essential (copper and zinc) metals were selected. The rainbow trout (Oncorhynchus mykiss) gut cell line (RTgutGC) was used to investigate bioavailability, bioreactivity and toxicity of the different metal species. Toxicity was measured using a multiple endpoint cytotoxicity assay, bioavailability by measuring intracellular metal concentration, and bioreactivity by quantification of mRNA level of the metal responsive genes, metallothionein (MT), glutathione reductase (GR) and zinc transporter 1 (ZnT1). Speciation calculations showed that silver and cadmium preferentially bind chloride, copper phosphate and bicarbonate, and zinc remained primarily as a free ion. Cysteine avidly complexed with all metals reducing toxicity, bioavailability and bioreactivity. Silver and copper toxicity was not affected by inorganic metal speciation, whereas cadmium and zinc toxicity was decreased by chloride complexation. Moreover, reduction of calcium concentration in the medium increased toxicity and bioavailability of cadmium and zinc. Bioavailability of silver and zinc was reduced by low chloride while cadmium bioavailability was increased by low chloride and in presence of bicarbonate. Copper bioavailability was not affected by the medium composition. Cadmium and silver were more bioreactive, independently from the medium composition, in comparison to copper and zinc (i.e., higher induction of MT and GR). Cadmium was the only metal able to induce MT in presence of cysteine. ZnT1 was induced by cadmium in low-chloride, by zinc in low-chloride low-calcium and by cadmium and copper in the bicarbonate media. Overall, this study demonstrates that metal complexation alone is not sufficient to explain metal toxicity, and that anion exchange mechanisms play a role in metal uptake and bioreactivity.

Water Hardness Improves the Antioxidant Response of Zinc-Exposed Goldfish (Carassius auratus)

Zinc (Zn), a heavy metal, is an essential element in fish; however, exposure to high concentrations causes oxidative stress. Water hardness reduces oxidative stress reactions caused by heavy metals. To confirm the effect of water hardness on oxidative stress caused by Zn, goldfish were exposed to various Zn concentrations (1.0, 2.0, and 5.0 mg/L) and water hardness (soft (S), hard (H), and very hard (V)). The activity of superoxide dismutase (SOD) and catalase (CAT) in plasma increased with 1.0, 2.0, and 5.0 mg/L of Zn, and decreased with H and V water hardness. The levels of H₂O₂ and lipid peroxide (LPO) increased with Zn above 1.0 mg/L and decreased with H and V of water hardness. Caspase-9 mRNA expression in the liver increased after 7 and 14 days of Zn exposure and decreased with H and V water hardness. It was confirmed that DNA damage was less dependent on H and V water hardness. Based on the results of this study, at least 1.0 mg/L Zn causes oxidative stress in goldfish, and a high level of apoptosis occurs when exposed for more than 7 days. It appears that the oxidative stress generated by Zn can be alleviated by water hardness of at least 270 mg/L CaCO₃. This study provides information on the relationship between the antioxidant response caused by heavy metals and water hardness in fish.

Copper and Zinc Treatments Alter the Thyroid Endocrine System in Zebrafish Embryos/Larvae

Copper (Cu²⁺) and zinc (Zn²⁺) are two kinds of heavy metals essential to living organisms. Cu²⁺ and Zn²⁺ at excessive concentrations can cause adverse effects on animals, but little is known about the thyroid-disrupting effects of these metals in fish, especially in the early developmental transition stage from embryos to larvae. Wild-type zebrafish embryos were used to expose to Cu²⁺ (0, 1.5, 15, and 150 μg/L) and Zn²⁺ (0, 20, 200, and 2000 μg/L) for 120 h. Thyroid hormone contents and transcriptional changes of the genes connected with the hypothalamic-pituitary-thyroid (HPT) axis were measured. Results showed that zebrafish embryos/larvae malformation rates were significantly increased in the Cu²⁺ and Zn²⁺ groups. Remarkably elevated thyroxine (T4) concentrations and reduced triiodothyronine (T3) concentrations were observed in Cu²⁺ and Zn²⁺ exposure fish. And the expression patterns of genes connected with the HPT axis were changed after Cu²⁺ and Zn²⁺ treatment. Based on principal component analysis (PCA) results, Zn²⁺ caused significant effects on the thyroid endocrine system at 200 μg/L, while Cu²⁺ resulted in thyroid disruption as low as 1.5 μg/L. In short, our study demonstrated that exposure to Cu²⁺ and Zn²⁺ induced developmental toxicity and thyroid disruption to zebrafish embryos/larvae.

Fish Embryo Acute Toxicity Testing and the RTgill-W1 Cell Line as In Vitro Models for Whole-Effluent Toxicity (WET) Testing: An In Vitro/In Vivo Comparison of Chemicals Relevant for WET Testing

The fathead minnow (Pimephales promelas) fish embryo acute toxicity (FET) test was compared to the fish gill cells (RTgill-W1) in vitro assay and to the fish larvae acute toxicity test to evaluate their sensitivity for whole-effluent toxicity (WET) testing. The toxicity of 12 chemicals relevant for WET testing was compared as proof of principle. The concentrations lethal to 50% of a population (LC50) of embryos were compared to those in fish larvae and to the 50% effect concentration (EC50) in RTgill-W1 cells from previous literature. Along with traditional FET endpoints (coagulation, somite development, tail detachment, and heartbeat), cardiotoxicity was evaluated for WET applicability. Heart rate was measured at LC20 and LC50 values of six subselected chemicals (Cd, Cu, Ni, ammonia, 3,4-dichloraniline, and benzalkonium chloride). In addition, the toxicity of Cd and Ni was evaluated in RTgill-W1 cells exposed in a hypoosmotic medium to evaluate the effect that osmolarity may have on metal toxicity. A significant correlation was found between the FET and larvae LC50 values but not between the RTgill-W1 EC50 and FET LC50 values. Although sensitivity to Ni and Cd was found to increase with hypoosmotic conditions for FET and RTgill-W1 cells, a correlation was only found with removal of Ni from the analysis. Hypoosmotic conditions increased sensitivity with a significant correlation between RTgill-W1 cells and larvae. Cardiotoxicity was shown in three of the five subselected chemicals (Cd, Cu, and 3,4-dichloroaniline). Overall, both in vitro alternative models have shown good predictability of toxicity in fish in vivo for WET chemicals of interest. Environ Toxicol Chem 2022;41:2721-2731. © 2022 SETAC.

Molecular mechanisms of zinc toxicity in the potworm Enchytraeus crypticus, analysed by high-throughput gene expression profiling

Zinc (Zn) is known to be relatively toxic to some soil-living invertebrates including the ecologically important enchytraeid worms. To reveal the molecular mechanisms of zinc toxicity we assessed the gene expression profile of Enchytraeus crypticus (Enchytraeidae), exposed to the reproduction effect concentrations EC₁₀ and EC₅₀, over 4 consecutive days, using a high-throughput microarray (species customized). Three main mechanisms of toxicity to Zn were observed: 1) Zn trafficking (upregulation of zinc transporters, a defence response to regulate the cellular zinc level), 2) oxidative stress (variety of defence mechanisms, triggered by Reactive Oxygen Species (ROS)), and 3) effects on the nervous system (possibly the primary lesion explaining the avoidance behaviour and also why enchytraeids are relatively susceptible to Zn). The adverse outcome at the organism level (reproduction EC₅₀) could be predicted based on gene expression (male gonad development, oocyte maturation), with Zn at the EC₅₀ affecting processes related to higher stress levels. The gene expression response was time-dependent and reflected the cascade of events taking place over-time. The 1 to 4 days of exposure design was a good strategy as it captured the time for sequence of events towards zinc adverse outcomes in E. crypticus.

Direct and Delayed Mortality of Ceriodaphnia dubia and Rainbow Trout Following Time-Varying Acute Exposures to Zinc

The potential for delayed mortality following short-term episodic pollution events was evaluated by exposing cladocerans (Ceriodaphnia dubia) and rainbow trout (Oncorhynchus mykiss) to zinc (Zn) in various 1- to 48-h and 1- to 96-h exposures, respectively, followed by transferring the exposed organisms to clean water for up to 47 h for C. dubia and up to 95 h for trout for additional observation. For C. dubia, 1-h exposures of up to 3790 µg Zn/L never resulted in mortality during the actual Zn exposures, but by 48 h, a 1-h exposure to 114 µg/L, a concentration similar to the present US national water quality acute criterion for the test water conditions, ultimately killed 70% of C. dubia. With C. dubia, the speed of action of Zn toxicity was faster for intermediate concentrations than for the highest concentrations tested. For rainbow trout, pronounced delayed mortalities by 96 h only occurred following ≥8-h exposures. For both species, ultimate mortalities from Zn exposures ≤8 h mostly presented as delayed mortalities, whereas for exposures ≥24 h, almost all ultimate mortalities presented during the actual exposure periods. With Zn, risks of delayed mortality following exposures to all concentrations tested were much greater for the more sensitive, small-bodied invertebrate (C. dubia) than for the less sensitive, larger-bodied fish (rainbow trout). These results, along with previous studies, show that delayed mortality is an important consideration in evaluating risks to aquatic organisms from brief, episodic exposures to some substances. Environ Toxicol Chem 2021;40:2484-2498. © 2021 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. This article has been contributed to by US Government employees and their work is in the public domain in the USA.

Evaluating costs of heavy metal tolerance in a widely distributed, invasive butterfly

Organismal tolerance to environmental pollution is thought to be constrained by fitness costs, where variants with higher survival in polluted environments have lower performance in nonpolluted environments. Yet, costs are not always detected in empirical studies. One hypothesis suggests that whether tolerance costs emerge depends on the degree of heterogeneity populations experience with respect to pollution exposure. For instance, in populations confined to local environments where pollution is persistent, selection may favour alleles that enhance pollution tolerance but reduce performance in nonpolluted environments (costs). However, in broadly distributed populations that undergo selection in both polluted and nonpolluted patches, costs should be eroded. Understanding tolerance costs in broadly distributed populations is relevant to management of invasive species, which are highly dispersive, wide ranging, and often colonize disturbed or polluted patches such as agricultural monocultures. Therefore, we conducted a case study quantifying costs of tolerance to zinc pollution (a common heavy metal pollutant) in wild cabbage white butterflies (Pieris rapae). This wide ranging, highly dispersive and invasive pest periodically encounters metal pollution by consuming plants in urban and agricultural settings. In contrast to expected costs of tolerance, we found that cabbage white families with greater zinc tolerance also produced more eggs and had higher reproductive effort under nonpolluted conditions. These results contribute to a more general hypothesis of why costs of pollution tolerance vary across studies: patchy selection with pollutants should erode costs and may favour genotypes that perform well under both polluted and nonpolluted conditions. This might partly explain why widely distributed invasive species are able to thrive in diverse, polluted and nonpolluted habitats.

Principal Components and Hierarchical Cluster Analyses of Trace Metals and Total Hydrocarbons in Gills, Intestines and Muscles of Clarias gariepinus (Burchell, 1822)

The aim of the study was to comparatively analyze the interrelationships among iron (Fe), manganese (Mn), zinc (Zn), copper (Cu), lead (Pb), cadmium (Cd), chromium (Cr) and total hydrocarbons (THCs) in the gills, intestines and muscles of Clarias gariepinus collected from Osse River, Nigeria, between the periods of April, 2013 to September, 2014. The trace metals in the fish tissues were analyzed using Atomic Absorption Spectrophotometer (AAS, Philips model PU 9100), while total hydrocarbons were analyzed using High Performance Liquid Chromatograph (HPLC,Prominence Dual brand from HGE) equipped with a detector Shimadzu UV-Visible (UV-Vis Prominence SPD 20 A). The concentrations of trace metals and THCs in the tissues were subjected to principal component analysis (PCA), in conjunction with hierarchical cluster analysis (HCA), backed up by correlation analysis (CA). In the most prioritized component among the hierarchies of contaminants, characterized as principal component 1, results of communality extractions and rotated component matrices revealed the order of contaminants was Mn > Cu > Zn > Fe > Cr in the intestines, Cr > Cu > THCs > Mn > Fe in the muscle, while Pb > Cr > Fe > Mn was the order in the gills of the fish. Iron inhibited accumulation of the other trace metals in the gills, where its threshold of essentiality was maximal. Noteworthy is the fact that Mn and Cu were the most active components in the muscle and concurrently of excess concentrations in the tissue, which is the major edible part of fish, and constitutes its main body weight, hence holds its nutritional and economic values. High level of variability which occurred in the toxicant profile across the tissues of C. gariepinus is a function of uptake route, varied organ functions and specificity of tissue permeability of the compared organs. The study demonstrated variability in organ accumulation capacity and toxicant's competitiveness irrespective of bioavailability. The study provides data useful for future ecotoxicological studies and safety of consumers of the fish.

The bioaccumulation of waterborne zinc in tissues of silver catfish (Rhamdia quelen) and its effect on biochemical parameters

Silver catfish (Rhamdia quelen) is a fish species with neotropical distribution, and is a potential model organism to study polluted environment. The aim of this study is to analyze the response of silver catfish to environmental concentrations of waterborne zinc (Zn) over 96 h. Significant metal accumulation was seen in gill, intestine and liver tissues. No significant accumulation was seen in muscle tissue. Lipid peroxidation increased in the brain, and decreased in the muscle and liver at all levels of exposure. Zinc exposure led to decreased protein carbonyl levels in the brain and increased levels in the liver. The activity of catalase in the liver was reduced for all exposed groups. Glutathione S-transferase activity decreased in the brain at the highest level of exposure and in the liver at all Zn concentrations tested. Non-protein thiols increased in the muscle and in the gills after exposure. Ascorbic acid levels increased in the brain and in the gills. Exposure to Zn also altered the metabolic parameters, causing decreased lactate and ammonia levels in the muscle, and decreased glycogen in the liver. Zinc exposure increased ammonia and amino acid levels in the liver, and increase glycogen and amino acid levels in muscle tissue. Our results demonstrate that exposure to environmentally relevant concentrations of Zn led to accumulation of metals in the tissues of silver catfish, with significant changes in biochemical parameters.

Acute exposure to an environmentally relevant concentration of diclofenac elicits oxidative stress in the culturally important galaxiid fish Galaxias maculatus

Diclofenac is a nonsteroidal anti-inflammatory drug (NSAID) of growing concern in aquatic environments worldwide; nevertheless, knowledge of its effects on aquatic biota is restricted to a few model species with limited information regarding its mechanisms of impact. In the present study, diclofenac accumulation, its effects on metabolic rate, ionoregulation, and oxidative stress were examined at environmentally relevant (0.17 µg L^-1 ) and elevated (763 µg L^-1 ) concentrations in a culturally and economically important galaxiid fish, inanga (Galaxias maculatus), from the Southern Hemisphere. This species is among the most widespread freshwater fish in the world but its sensitivity to emerging contaminants is unknown. Following an acute 96-h exposure, bioconcentration of diclofenac was measured in the inanga whole-body, resulting in an estimated bioconcentration factor of 87 for the 0.17-µg L^-1 exposure concentration, approaching values where transfer through the food chain should be considered. Lipid peroxidation in the liver was significantly elevated at both 0.17- and 763-µg L^-1 exposure concentrations but lipid peroxidation in the kidney and gill decreased after diclofenac exposure. Catalase activity was also elevated in the liver of inanga but activity decreased in the gill. There were no effects of diclofenac on metabolic rate or ion (sodium and calcium) influx rates. These data indicate that toxicologically relevant adverse outcomes and bioconcentration of diclofenac at environmentally relevant levels warrant additional study in this important fish. Environ Toxicol Chem 2018;37:224-235. © 2017 SETAC.