Effects of dietary calcium and cadmium on cadmium accumulation, calcium and cadmium uptake from the water, and their interactions in juvenile rainbow trout

Cadmium impacts on calcium mineralization of zebrafish skeletal development and behavioral impairment

Cadmium (Cd) poses significant risks to aquatic organisms due to its toxicity and ability to disrupt the cellular processes. Given the similar atomic radius of Cd and calcium (Ca), Cd may potentially affect the Ca homeostasis, which can lead to impaired mineralization of skeletal structures and behavioral abnormalities. The formation of the spinal skeleton involves Ca transport and mineralization. In this study, we conducted an in-depth investigation on the effects of Cd at environmental concentrations on zebrafish (Danio rerio) skeletal development and the underlying molecular mechanisms. As the concentration of Cd increased, the accumulation of Cd in zebrafish larvae also rose, while the Ca content decreased significantly by 3.0 %-57.3 %, and vertebral deformities were observed. Transcriptomics analysis revealed that sixteen genes involved in metal absorption were affected. Exposure to 2 µg/L Cd significantly upregulated the expression of these genes, whereas exposure to 10 µg/L resulted in their downregulation. Consequently, exposure of zebrafish larvae to 10 µg/L of Cd inhibited the body segmentation growth and skeletal mineralization development by 29.1 %-56.7 %. This inhibition was evidenced by the downregulation of mineral absorption genes and decreased Ca accumulation. The findings of this study suggested that the inhibition of skeletal mineralization was likely attributed to the disruption of mineral absorption, thus providing novel insights into the mechanisms by which metal pollutants inhibit the skeletal development of fish.

Cadmium induced bioaccumulation, histopathology, gene regulation in fish and its amelioration - A review

Different anthropogenic activities as well as natural sources contribute enormously towards various heavy metal contaminations in aquatic habitats. Cadmium (Cd) is one of most prevalent and toxic heavy metals with a long half life. Unlike terrestrial animals, exposure of Cd in fishes may happen not only through feeds but also from its habitat water. Bioaccumulation of Cd in fishes occurs in many tissues, but mainly in gill, liver, kidney, skin, and muscle. The concentrations of Cd in fish tissues depend upon the extent and duration of Cd exposure, species and age of fishes, dietary minerals and antioxidant concentrations, and habitat water quality. Specific histopathological observations in liver, kidney, and gill are useful to understand the effects of Cd, which could help to determine the ameliorating methods to be adopted. Exposure of Cd exerts several adverse effects on general growth and development, reproductive processes, osmoregulation, morphological and histological structures, stress tolerance, and endocrine system, mainly due to changes in biological functions induced by differential expressions of several genes related to oxidative stress, apoptosis, inflammation, immunosuppressions, genotoxicity, Cd chelation and carbohydrate metabolism. Chronic biomagnifications of Cd exceeding the permitted level may be harmful not only to the fishes itself but also to humans through food chains. Amelioration of such toxic heavy metal that has been categorized as a potent carcinogenic in humans is of utmost importance. Main modes of amelioration encompas reducing oxidative damages by promoting the antioxidative defenses, decreasing Cd absorption, increasing excretion through excretory system and improving the tolerance of fishes to Cd toxicity. Many amelioration measures such as use of minerals (for example, zinc, calcium, and iron), vitamins (vitamin C, A, and E), different herbs, probiotics and other agents (taurine, bentonite, chitosan, zeolite, and metallothionein) have been explored for their effective roles to reduce Cd bioaccumulation and toxicity symptoms in fishes. The present review discusses bioaccumulation of Cd, histopathological alterations, oxidative stress, synergism-antagonism, and gene regulation in different tissues, and its amelioration measures in fishes.

Tracing the oomycete pathogen Saprolegnia parasitica in aquaculture and the environment

Saprolegnia parasitica causes saprolegniosis, a disease responsible for significant economic losses in aquaculture and declines of fish populations in the wild, but the knowledge of its distribution and prevalence in the environment is limited. We developed a fast, sensitive and specific S. parasitica droplet digital PCR (ddPCR) assay and demonstrated its applicability for the detection and quantification of the pathogen in environmental samples: swab DNA collected from the host (trout skin, surface of eggs) and environmental DNA extracted from water. The developed assay was used to assess how abiotic (i.e. physico-chemical parameters of the water) and biotic (health status of the host) factors influence the S. parasitica load in the environment. The pathogen load in water samples was positively correlated with some site-specific abiotic parameters such as electrical conductivity (EC) and calcium, while fluorides were negatively correlated, suggesting that physico-chemical parameters are important for determining S. parasitica load in natural waters. Furthermore, skin swabs of injured trout had significantly higher pathogen load than swabs collected from healthy fish, confirming that S. parasitica is a widespread opportunistic pathogen. Our results provide new insights into various environmental factors that influence the distribution and abundance of S. parasitica.

Cadmium toxicity: A role in bone cell function and teeth development

Cadmium (Cd) is a widespread environmental contaminant that causes severe bone metabolism disease, such as osteoporosis, osteoarthritis, and osteomalacia. The present review aimed to explore the molecular mechanisms of Cd-induced bone injury starting from bone cell function and teeth development. Cd inhibits the differentiation of bone marrow mesenchymal stem cells (BMSCs) into osteoblasts, and directly causes BMSC apoptosis. In the case of osteoporosis, Cd mainly affects the activation of osteoclasts and promotes bone resorption. Cd-induces osteoblast injury and oxidative stress, which causes DNA damage, mitochondrial dysfunction, and endoplasmic reticulum stress, resulting in apoptosis. In addition, the development of osteoarthritis (OA) might be related to Cd-induced chondrocyte damage. The high expression of metallothionein (MT) might reduce Cd toxicity toward osteocytes. The toxicity of Cd toward teeth mainly focuses on enamel development and dental caries. Understanding the effect of Cd on bone cell function and teeth development could contribute to revealing the mechanisms of Cd-induced bone damage. This review explores Cd-induced bone disease from cellular and molecular levels, and provides new directions for removing this heavy metal from the environment.

Can human nutrition be improved through better fish feeding practices? a review paper

Achieving Sustainable Development Goal 2 of zero hunger and malnutrition by 2030 will require dietary shifts that include increasing the consumption of nutrient dense foods by populations in low- and middle-income countries. Animal source foods are known to be rich in a number of highly bioavailable nutrients that otherwise are not often consumed in the staple-food based diets of poorer populations throughout the world. Fish is the dominant animal source food in many low- and middle-income countries in the global south and is available from both fisheries and aquaculture. Consumers often perceive that wild caught fish have higher nutritional value than fish produced through aquaculture, and this may be true for some nutrients, for example omega-3 fatty acid content. However, there is potential to modify the nutritional value of farmed fish through feeds and through production systems, illustrated by the common practice of supplementing omega-3 fatty acids in fish diets to optimize their fatty acid profile. This manuscript reviews the evidence related to fish feeds and the nutritional composition of fish with respect to a number of nutrients of interest to human health, including iron, zinc, vitamins A and D, selenium, calcium, and omega-3 fatty acids, with low- and middle-income country populations in mind. In general, we find that the research on fortification of fish diet particularly with vitamins and minerals has not been directed toward human health but rather toward improvement of fish growth and health performance. We were unable to identify any studies directly exploring the impact of fish feed modification on the health of human consumers of fish, but as nutrition and health rises in the development agenda and consumer attention, the topic requires more urgent attention in future feed formulations.

Mechanisms of Ca2+ uptake in freshwater and seawater-acclimated killifish, Fundulus heteroclitus, and their response to acute salinity transfer

Killifish (Fundulus heteroclitus) has been extensively used as a model for ion regulation by euryhaline fishes. Na⁺ and Cl^- dynamics have been well studied in killifish, but few studies have addressed that of Ca²⁺. Therefore, this study aimed to characterize Ca²⁺ fluxes in freshwater (FW) and seawater (SW)-acclimated killifish, their response to salinity transfer, and to elucidate the mechanisms of Ca²⁺ influx in FW and SW. SW killifish displayed a significantly higher Ca²⁺ influx rate than that of FW fish, while Ca²⁺ efflux rates were comparable in both salinities. Ca²⁺ influx was saturable in FW (K_m = 78 ± 19 µmol/L; J_max = 53 ± 3 nmol/g/h) and influx by SW killifish was linear up to 7 mmol/L Ca²⁺. In SW-acclimated fish, 36% of Ca²⁺ influx was attributed to "intestinal Ca²⁺ intake", likely caused by drinking, whereas intestinal Ca²⁺ intake in FW contributed to < 2% of total. Throughout the study, results suggested that "cation competition" in SW modulates Ca²⁺ influx. Therefore, we hypothesized that SW-acclimated fish actually have a higher affinity Ca²⁺ influx system than FW-acclimated fish but that it is competitively inhibited by competing SW cations. In agreement with this cation competition hypothesis, we demonstrated for the first time that "extra-intestinal" Ca²⁺ influx was inhibited by Mg²⁺ in both FW and SW-acclimated killifish. Following acute salinity transfer, extra-intestinal Ca²⁺ influx was rapidly regulated within 12-24 h, similar to Na⁺ and Cl^-. Ca²⁺ influx in FW was inhibited by La³⁺, an epithelial Ca²⁺ channel blocker, whereas La³⁺ had no significant effect in SW.

Waterborne Cd2+ weakens the immune responses of blood clam through impacting Ca2+ signaling and Ca2+ related apoptosis pathways

Exposure to heavy metals such as Cadmium (Cd) may exert detrimental impacts on the immune responses of marine bivalve species. However, the immunotoxicity of Cd on blood clams remains unknown to date. Furthermore, though Cd²⁺ is known to compete with calcium (Ca²⁺) ions for their binding sites in cells and inhibit Ca²⁺ influx, whether Cd²⁺ weakens the immune responses of marine bivalves through inducing intracellular Ca²⁺ disorders still remains unclear. Therefore, the immunotoxicity of Cd²⁺ at different waterborne Ca²⁺ concentrations on blood clam, Tegillarca granosa, were investigated in the present study. Results obtained demonstrated that the total number, phagocytic activity, and red granulocytes ratio of the haemocytes were all significantly reduced after 10 days exposure of individuals to 25 μg/L Cd²⁺. However, when the waterborne Ca²⁺ concentrations were elevated by 10% and 20% (approximately 370 and 410 mg/L, respectively), mitigation effects on the immune responses of individuals were detected. In addition, though the expressions of genes from the Ca²⁺ signaling and Ca²⁺-related apoptosis pathways were significantly altered by Cd²⁺ exposure, the expression patterns of these genes were similar to that of the control when the waterborne Ca²⁺ concentrations were elevated, suggesting a relieving effect of waterborne Ca²⁺ on Cd²⁺ induced toxicity to haemocytes. The results obtained in the present study revealed that waterborne Cd²⁺ may hamper the immune responses of T. granosa through influencing Ca²⁺ signaling and Ca²⁺-related apoptosis pathways, which can be partially mitigated by elevating the waterborne Ca²⁺ concentrations.

Physiological impacts and bioaccumulation of dietary Cu and Cd in a model teleost: The Amazonian tambaqui (Colossoma macropomum)

Increasing anthropogenic activities in the Amazon have led to elevated metals in the aquatic environment. Since fish are the main source of animal protein for the Amazonian population, understanding metal bioaccumulation patterns and physiological impacts is of critical importance. Juvenile tambaqui, a local model species, were exposed to chronic dietary Cu (essential, 500 μg Cu/g food) and Cd (non-essential, 500 μg Cd/g food). Fish were sampled at 10-14, 18-20 and 33-36 days of exposure and the following parameters were analyzed: growth, voluntary food consumption, conversion efficiency, tissue-specific metal bioaccumulation, ammonia and urea-N excretion, O₂ consumption, P_crit, hypoxia tolerance, nitrogen quotient, major blood plasma ions and metabolites, gill and gut enzyme activities, and in vitro gut fluid transport. The results indicate no ionoregulatory impacts of either of the metal-contaminated diets at gill, gut, or plasma levels, and no differences in plasma cortisol or lactate. The Cd diet appeared to have suppressed feeding, though overall tank growth was not affected. Bioaccumulation of both metals was observed. Distinct tissue-specific and time-specific patterns were seen. Metal burdens in the edible white muscle remained low. Overall, physiological impacts of the Cu diet were minimal. However dietary Cd increased hypoxia tolerance, as evidenced by decreased P_crit, increased time to loss of equilibrium, a lack of plasma glucose elevation, decreased plasma ethanol, and decreased NQ during hypoxia. Blood O₂ transport characteristics (P₅₀, Bohr coefficient, hemoglobin, hematocrit) were unaffected, suggesting that tissue level changes in metabolism accounted for the greater hypoxia tolerance in tambaqui fed with a Cd-contaminated diet.

Interactive effects of chronic dietary selenomethionine and cadmium exposure in rainbow trout (Oncorhynchus mykiss): A preliminary study

The present study investigated the interactive effects of dietary cadmium (Cd) and selenium (Se) on the tissue-specific (liver, kidney, and muscle) accumulation of these two elements, hepatic oxidative stress response, and morphometrics in rainbow trout (Oncorhynchus mykiss) during chronic exposure. Fish were exposed to elevated dietary Cd (45 μg g^-1 dry wt.), and medium (10 μg g^-1 dry wt.) or high (45 μg g^-1 dry wt.) dietary selenium (added as selenomethionine), both alone and in combination, for 30 days. Exposure to dietary Cd alone caused oxidative stress in fish as reflected by reduced thiol redox (GSH:GSSG), increased lipid peroxidation, and induction of anti-oxidative enzymes (catalase, superoxide dismutase, and glutathione peroxidase) in the liver. Also, an increase in tissue-specific Cd burden and impaired morphometrics (hepato-somatic index and condition factor) were also recorded in fish following exposure to dietary Cd. In contrast, the dietary co-exposure to Cd and Se (at both medium and high doses) resulted in a decrease in Cd burden in the liver and kidney of fish. However, co-exposure to medium, but not high, dose of dietary Se completely alleviated Cd-induced oxidative stress and impaired morphometrics in fish, indicating that the reduced Cd tissue burden might not have been the primary factor behind the amelioration of Cd toxicity by Se. Overall, our study demonstrated that the protective effect of Se against the chronic Cd toxicity in fish is mainly mediated by the anti-oxidative properties of Se, but this protective effect is dose-specific and occurs only at a moderate exposure dose.

The simultaneous uptake of dietary and waterborne Cd in gastrointestinal tracts of marine yellowstripe goby Mugilogobius chulae

Aquatic animals under waterborne metal exposure are also very likely exposed to elevated dietary metals. This study quantified the simultaneous uptake of dietary and waterborne Cd in gastrointestinal tracts (GT) of marine yellowstripe goby using a dual stable isotope tracer method. The Cd spiked diet (10-100 μg g^-1, ¹¹¹Cd as tracers) were fed to the fish as a single meal, and then the fish were exposed to waterborne Cd (0-500 μg L^-1, ¹¹³Cd as tracers) for 48 h, during which the time-course uptake of Cd in the stomach and intestine was determined. The findings revealed that the dietary Cd uptake mainly occurred within 12 h after feeding. The fish exposed to 500 μg L^-1 waterborne Cd showed significantly lower Cd assimilation efficiency (2.07%) than the control group (3.48%) at the dietary Cd of 100 μg g^-1. Moreover, during 4-12 h when there was chyme in the GT, the waterborne Cd uptake in the intestine was lowest but the stomach showed the highest waterborne Cd uptake rate. The uptake of dietary and waterborne Cd, and the relative importance of dietary vs waterborne Cd was positively correlated with the Cd concentration in the chyme. Overall, this research demonstrated that there was interaction between dietary and waterborne Cd uptake in the GT of marine fish. The simultaneous uptake of metal from two routes is far more complex than the situation of a single route of metal uptake, which should be evaluated in determining metal bioaccumulation and toxicity in both laboratory and field metal exposure scenario.

Toxicological perspective on the osmoregulation and ionoregulation physiology of major ions by freshwater animals: Teleost fish, crustacea, aquatic insects, and Mollusca

Anthropogenic sources increase freshwater salinity and produce differences in constituent ions compared with natural waters. Moreover, ions differ in physiological roles and concentrations in intracellular and extracellular fluids. Four freshwater taxa groups are compared, to investigate similarities and differences in ion transport processes and what ion transport mechanisms suggest about the toxicity of these or other ions in freshwater. Although differences exist, many ion transporters are functionally similar and may belong to evolutionarily conserved protein families. For example, the Na+ /H+ -exchanger in teleost fish differs from the H+ /2Na+ (or Ca2+ )-exchanger in crustaceans. In osmoregulation, Na+ and Cl- predominate. Stenohaline freshwater animals hyperregulate until they are no longer able to maintain hypertonic extracellular Na+ and Cl- concentrations with increasing salinity and become isotonic. Toxic effects of K+ are related to ionoregulation and volume regulation. The ionic balance between intracellular and extracellular fluids is maintained by Na+ /K+ -adenosine triphosphatase (ATPase), but details are lacking on apical K+ transporters. Elevated H+ affects the maintenance of internal Na+ by Na+ /H+ exchange; elevated HCO3- inhibits Cl- uptake. The uptake of Mg2+ occurs by the gills or intestine, but details are lacking on Mg2+ transporters. In unionid gills, SO42- is actively transported, but most epithelia are generally impermeant to SO42- . Transporters of Ca2+ maintain homeostasis of dissolved Ca2+ . More integration of physiology with toxicology is needed to fully understand freshwater ion effects. Environ Toxicol Chem 2017;36:576-600. Published 2016 Wiley Periodicals Inc. on behalf of SETAC. This article is a US government work and, as such, is in the public domain in the United States of America.

Linking Oxidative Stress and Magnitude of Compensatory Responses with Life-Stage Specific Differences in Sensitivity of White Sturgeon (Acipenser transmontanus) to Copper or Cadmium

Sensitivity of white sturgeon (Acipenser transmontanus) to copper (Cu) or cadmium (Cd) has been shown to significantly differ as a function of life-stage. This study investigated oxidative stress, metal homeostasis, and associated compensatory responses as potential mechanisms of this sensitivity pattern in three early life-stages. Sturgeon were most sensitive to Cu at 15 days post hatch (dph), which was accompanied by a significant increase in lipid peroxidation (LPO). Genes involved with amelioration of oxidative stress were significantly less inducible at this stage than in older, less sensitive fry. At 48 dph, acute lethality of sturgeon exposed to Cd was greatest and body LPO was significantly induced by 3.5-fold at 5 μg Cd/L. Moreover, there was a small but significant increase in antioxidative responses. At 139 dph, sturgeon were most tolerant to Cu and Cd and accumulation of these metals was least. Also, expression of metallothionein (MT) and apoptotic genes were greatest while expression of metal transporters was reduced and concentration of LPO was not different from controls. Our results suggest that life-stage specific sensitivity of white sturgeon to metals is complex, encompassing differences in the ability to mount compensatory responses important for metal homeostasis and combating oxidative stress and concomitant damages.

Interactions of waterborne and dietborne Pb in rainbow trout, Oncorhynchus mykiss: Bioaccumulation, physiological responses, and chronic toxicity

In Pb-contaminated environments, simultaneous exposure to both waterborne and dietborne Pb is likely to occur. This study examined the potential interactive effects of these two pathways in juvenile rainbow trout that were exposed to Pb in the water alone, in the diet alone, and in combination for 7 weeks. The highest waterborne Pb concentration tested (110μgL(-1)) was approximately equivalent to the 7-week LC20 (97μgL(-1)) measured in a separate trial, while the lowest was a concentration often measured in contaminated environments (8.5μgL(-1)). The live diet (10% daily ration on a wet mass basis) consisted of oligochaete worms (Lumbriculus variegatus) pre-exposed for 28days to the same waterborne Pb concentration, and the highest dietary dosing rate to the trout was 12.6μg Pb g fish(-1)day(-1). With waterborne exposure, whole body Pb burden increased to a greater extent in the worms than in the fish. Nonetheless, in trout waterborne exposure still resulted in 20-60-fold greater Pb accumulation compared to dietborne Pb exposure. However, combined exposure to both waterborne and dietborne Pb reduced the whole body accumulation extensively at waterborne Pb>50μgL(-1), with similar antagonistic interaction in liver and carcass (but not gill or gut) at a lower threshold of 20μgL(-1). Growth effects in trout were minimal with marginal reductions in the dietborne and combined exposures seen only at 110μgL(-1). Chronic Pb exposure reduced lipid and carbohydrates level in the worms by 50% and 80% respectively, while protein was unchanged, so growth effects in trout may have been of indirect origin. After 7 weeks, Ca(2+) homeostasis in the trout was unaffected, but there were impacts on Na(+). Blood Na(+) was reduced in waterborne and dietborne exposures, while gut Na(+)/K(+) ATPase activities were reduced in waterborne and combined exposures. This study is the first, to our knowledge to examine the interaction of waterborne and dietborne Pb exposure in fish. While physiological impacts of Pb were observed in both worms and fish, higher concentrations of dietborne Pb actually protected fish from waterborne Pb bioaccumulation and these effects. The impacts of metals on diet quality should not be neglected in future dietborne toxicity studies using live prey.

Feeding reduces waterborne Cu bioaccumulation in a marine rabbitfish Siganus oramin

Waterborne metal uptake has been extensively studied and dietary metal assimilation is increasingly recognized in fish, whilst the interaction between the two uptake routes is largely overlooked. This study compared the waterborne Cu bioaccumulation ((65)Cu as tracer) in a juvenile rabbitfish at different feeding regimes (starvation (SG), feeding normal diet (NDG) or diet supplemented with extra Cu (DCG)) to test the hypothesis that feeding can influence waterborne metal uptake in marine fish. NDG and DCG diet was fed as a single meal and then all fish were exposed to waterborne (65)Cu for 48 h, during which the time course sampling was conducted to determine (65)Cu bioaccumulation, chyme flow and dietary Cu assimilation. The results revealed that SG fish accumulated the highest (65)Cu, followed by NDG (61% of SG), whilst DCG fish accumulated the lowest (65)Cu (34% of SG). These results suggested a protective effect of feeding against waterborne Cu bioaccumulation. This effect was most notable between 10 min and 16 h when there was chyme in gastrointestinal tract (GT). Dietary Cu assimilation mainly occurred before 16 h after feeding. Waterborne (65)Cu influx rate in the GT was positively correlated with (65)Cu contents of chyme in NDG, whereas it was largely negatively correlated with (65)Cu contents of chyme in DCG. The waterborne Cu uptake in the GT was mainly influenced by the chyme flow and dietary Cu assimilation. Overall, our findings suggested that feeding has an important effect on waterborne metal uptake and that both the feeding status of the fish and the relative metal exposure through water and food should be considered in prediction of the metal bioaccumulation and biomonitoring programs.

Effects of salinity on metal uptake and metallothionein mRNA levels in the organs of tilapia exposed to cadmium, copper, and zinc ions

This study aimed to determine the effects of salinity on metal uptake and metallothionein (MT) mRNA levels in tilapia exposed to three metal ions. Male Oreochromis niloticus × O. aureus juveniles (hereafter, "tilapia") were exposed to various concentrations (100, 500, and 1 ppm) of metal ions (Cd(2+), Cu(2+) and Zn(2+)) in freshwater and water with two levels of salinity (10 and 20 ppt) for 7 days. Tests were then performed to investigate the effects of salinity on metal concentrations and MT mRNA induction in the test subjects' organs. Saline decreased cadmium (Cd) uptake and MT mRNA fold induction in various internal organs, but it did not enhance MT mRNA induction in the gills. Exposure to Cu(2+) caused greater copper (Cu) levels in the brains, intestines and livers, but Cu uptake in the intestines and kidneys occurred only at 10 ppm. MT mRNA induction caused by Cu(2+) was observed in various internal organs, but it occurred in the gills only at greater levels of salinity. Exposure at greater salinities also decreased zinc (Zn) uptake and MT mRNA induction in all organs except the gills. Although greater salinity decreased Cd and Zn uptake, the metal content in the water correlated with the MT mRNA levels in most of the organs, except for the intestines. In conclusion, metal accumulations in the livers and kidneys of tilapia correlated with MT mRNA levels. The levels of MT mRNA in the livers and kidneys of tilapia might therefore be used as biomarkers of exposure to Cd(2+), Cu(2+) and Zn(2+) in water of various salinities.

High dietborne Cu and Cd induced genotoxicity of Nile tilapia (Oreochromis niloticus)

In this study, the effects of fish diet contaminated with Cu, Cd and Cu+Cd on Nile tilapia, was demonstrated by evaluating its bioaccumulation in the muscle and by testing the cytogenetic profile. Fish exposed to diet contaminated with Cu, Cd or their mixture had a significant increase in the number of chromosomal abnormalities and an inhibition of the mitotic index. Our study revealed high muscle Cu or Cd content in fish fed with diet contaminated with high dietborne Cu, Cd, Cu and Cd. It also revealed that the chromosomal abnormalities were higher for fish fed diet Cd contaminated and Cu+Cd contaminated diets than those fed diet Cu contaminated diet. Thus, maybe fish diets contaminated with Cu, Cd, Cu+Cd induced genotoxicity and mutation. Also, maybe high concentrations of Cu and Cd in fish tissue resulted from feeding on Cu and Cd contaminated diets, are dangerous for human consumption.

Effects of Different Dietary Cadmium Levels on Growth and Tissue Cadmium Content in Juvenile Parrotfish, Oplegnathus fasciatus

This feeding trial was carried out to evaluate the effects of different dietary cadmium levels on growth and tissue cadmium content in juvenile parrotfish, Oplegnathus fasciatus, using cadmium chloride (CdCl₂) as the cadmium source. Fifteen fish averaging 5.5±0.06 g (mean±SD) were randomly distributed into each of twenty one rectangular fiber tanks of 30 L capacity. Each tank was then randomly assigned to one of three replicates of seven diets containing 0.30 (C₀), 21.0 (C₂₁), 40.7 (C₄₁), 83.5 (C₈₃), 162 (C₁₆₂), 1,387 (C_1,387) and 2,743 (C_2,743) mg cadmium/kg diet. At the end of sixteen weeks of feeding trial, weight gain (WG), specific growth rate (SGR) and feed efficiency (FE) of fish fed C₂₁ were significantly higher than those of fish fed C₈₃, C₁₆₂, C_1,387 and C_2,743 (p<0.05). Weight gain, SGR and FE of fish fed C₀, C₂₁ and C₄₁ were significantly higher than those of fish fed C₁₆₂, C_1,387 and C_2,743. Protein efficiency ratio of fish fed C₀, C₂₁ and C₄₁ were significantly higher than those of fish fed C_1,387 and C_2,743. Average survival of fish fed C₀, C₂₁, C₄₁ and C₁₆₂ were significantly higher than that of fish fed C_2,743. Tissue cadmium concentrations increased with cadmium content of diets. Cadmium accumulated the most in liver, followed by gill and then muscle. Muscle, gill and liver cadmium concentrations of fish fed C₀, C₂₁, C₄₁ and C₈₃ were significantly lower than those of fish fed C₁₆₂, C_1,387 and C_2,743. Based on the ANOVA results of growth performance and tissue cadmium concentrations the safe dietary cadmium level could be lower than 40.7 mg Cd/kg diet while the toxic level could be higher than 162 mg Cd/kg diet.

Zn-stimulated mucus secretion in the rainbow trout (Oncorhynchus mykiss) intestine inhibits Cd accumulation and Cd-induced lipid peroxidation

Interest in the interactions between dietary constituents in the gut is increasing, but information remains sparse. In this study rainbow trout were fed non-enriched (186.7±19.0 μg Zn g(-1) (dw)), enriched (20% increase) and hyper-enriched Zn (200% increase) diet for 21 d followed by a single meal of Cd-spiked food (188.6±9.9 μg Cd g(-1) (dw)). Intestinal, hepatic and renal Zn burdens were measured on Days 7, 14 and 21 and Cd concentrations in the same tissue were measured 48 h-post Cd exposure. Oxidative stress was measured as lipid peroxidation in dissected tissues and intestinal mucus was quantified as sialic acid using the thiobarbituric acid assay. Rainbow trout maintained on the hyper-enriched Zn diet experienced significantly increased intestinal mucus secretion (p<0.01), were the only treatment group not to accumulate Cd in the intestine, and there was also no increase in intestinal oxidative damage. Conversely, fish fed the non-enriched and enriched Zn diets did not produce greater than basal levels of intestinal mucus and accumulated significantly greater concentrations of Cd in the intestine (p<0.01) leading to significant localised Cd-induced lipid peroxidation (p<0.01). High levels of mucus production correlated to lower incidences of lipid peroxidation (r(2)=0.54, p<0.05). These results demonstrate that mucus production stimulated by a high Zn diet have an inhibitory effect on Cd accumulation in the intestine and on Cd-induced lipid peroxidation. Mechanistically, it is likely that the elevated mucus production provides a barrier to Cd uptake. This study describes how one dietary constituent directly modifies the gut environment which indirectly influences the fate of another ingested cation.

Non-invasive in vivo imaging of the ionic regimes along the gastrointestinal tract of a freshwater vertebrate model organism (Japanese medaka) using responsive photonic crystal beads

Microspherical photonic colloidal crystalline beads that are responsive to media ionic strength of cationic electrolytes have been developed for in vivo imaging of the morphology and concentration gradient of cationic electrolytes along the gastrointestinal (GI) tract of live Japanese medaka (Oryzias latipes). These responsive photonic beads were assembled from core-shell nano-sized particles with polystyrene-co-polyacrylic acid (PS-co-PAA) cores and poly(hydroxyethyl methacrylate-co-p-styrene sulfonate) (PHEMA-co-PSS) hydrogel shells. The three-dimensional orderly packing of these nano-sized core-shell particles gave rise to the photonic properties of the resultant colloidal crystalline array of microspheres. The cationic electrolyte-induced volume phase transition of the sulfonate-laden hydrogel shells of the nano-sized particles altered the lattice spacing among those particles and brought about the photonic responses of the colloidal crystalline beads. Unambiguous changes in the diffraction colour of the colloidal crystalline beads were observable under ordinary ambient light in solution media of increasing concentration of sodium chloride up to 500 mM. These photonic colloidal crystalline beads were found to possess enough structural integrity for in vivo imaging of the GI tract of live Japanese medaka. With the use of a conventional optical microscope, the gradient in the ionic strength of cationic electrolytes along the GI tract of live Japanese medaka larvae was readily revealed, with a lower electrolyte concentration in the mid-intestine (<50 mM) compared to that of the posterior-intestine (≥50 mM). Our results demonstrated the potential of stimuli-responsive photonic materials in bio-imaging applications.

In situ analysis of cadmium uptake in four sections of the gastro-intestinal tract of rainbow trout (Oncorhynchus mykiss)

This study links results from past in vitro and in vivo experiments, by implementing an in situ experiment in order to determine the relative importance for cadmium (Cd) uptake of different sections of the gastro-intestinal tract (GIT) of rainbow trout. Transport of Cd from four sections of the GIT of adult rainbow trout (~220 g) was individually examined by infusing ligated sections of the GIT in live, free-swimming fish with 50 μM Cd spiked with radiolabelled (109)Cd (0.5 μCi ml(-1)). Fish were exposed for an 8-h period. The percentage of the total injected (109)Cd which was internalized from the different segments was only between ~0.1 and ~7%, indicating low uptake efficiency. The stomach is the most important GIT segment for Cd transport into the internal compartment of the animal, while the posterior intestine also plays a significant role. The majority of (109)Cd recovered at the end of the flux period was detected within gut material (ranging from 28 to 95%); the portion of Cd which was internalized was largely found in the carcass (32 to 60%). Distribution between the measured organs varied with uptake from the various GIT sections. Our results also confirm that the GIT acts as a protective barrier against Cd uptake from dietary exposure.

In vitro characterization of calcium transport along the gastrointestinal tract of freshwater rainbow trout Oncorhynchus mykiss

Using an in vitro gut-sac technique, this study examined the mechanisms of calcium (Ca) uptake along the gastrointestinal tract (GIT) of rainbow trout Oncorhynchus mykiss. Ca uptake into three different compartments (mucous-bound, mucosal epithelium and blood space) of four distinct GIT segments (stomach, anterior intestine, mid intestine and posterior intestine) was monitored after luminal exposure to 10 mM Ca saline (radiolabelled with (45) Ca). Ca transport was determined to be both time-dependent and concentration-dependent. The concentration-dependent kinetics of Ca uptake was investigated using varying luminal concentrations of Ca (1, 10, 30, 60 and 100 mM). In the blood-space compartment, Ca uptake was saturable at high Ca concentrations in the mid intestine (suggesting mediated transport), while linear uptake was found in the other gut segments. In the mucous-bound and mucosal epithelium compartments, however, saturation kinetics were found for most GIT segments, also suggesting mediated transport. Manipulation of serosal saline osmotic pressure with mannitol demonstrated that Ca uptake was not greatly affected by solvent drag. Elevated mucosal cadmium (Cd) did not appear to inhibit Ca uptake into the blood space in any of the GIT sections, and Ca uptake did not appear to be sodium dependent. Maximum transport capacities for Ca and Cd were found to be comparable between the gills and gut, but affinities were much higher at the gills (up to 3000 times).

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.

Salinity effects on the bioavailability of aqueous metals for the estuarine killifish Fundulus heteroclitus

Estuarine organisms experience varying salinity conditions on a daily and seasonal basis, and these fluctuations could influence the amount of metal accumulated from the aqueous phase. The present study experimentally assessed the role of salinity (0, 2, 6, 12, and 25 ppt) on the uptake of As, Cd, Cr, inorganic Hg [Hg(II)], and methylmercury (MeHg) into the euryhaline killifish (Fundulus heteroclitus) from the aqueous phase using gamma-emitting radioisotopes. Patterns of metal uptake as a function of salinity varied by metal. Chromium showed no relationship with salinity; Cd, which was most affected by salinity, showed an inverse relationship; and As, Hg(II), and MeHg uptake increased as salinity increased from 0 ppt to 25 ppt. Arsenic (salinities ≤ 6 ppt) and Cr were regulated by the fish, whereas Cd, Hg(II), and MeHg were not. Cadmium, Hg(II), and MeHg are chloro-complexed, increasing bioavailability for Hg(II) and MeHg, and reducing bioavailability for Cd. Concentration factors (CFs) were >1 at all salinities for Cd, Hg(II), and MeHg, indicating that the fish were more enriched in the metal than the surrounding water, whereas As and Cr CFs were <1 at all salinities. Uptake rate constants (k(u)s) were highest for MeHg (0.79-2.29 L g(-1) d(-1)), followed by Hg(II), Cd, Cr, and lowest for As (0.0004-0.0008 L g(-1) d(-1)). Tissue distribution of each metal was determined by dissections. Data for Cd showed that as salinity increased, the concentration of this metal increased in the viscera, whereas it decreased in the head and gills, suggesting that drinking to osmoregulate may account for a portion of Cd uptake from the aqueous phase in marine fish.

Effects of montmorillonite on alleviating dietary Cd-induced oxidative damage in carp (Carassius auratus)

The present study was designed to investigate the effects of montmorillonite (MMT) on dietary Cd-induced oxidative damage in liver and kidney of carp (Carassius auratus). One hundred eighty carp were randomly divided into four groups and fed with a basal diet, a basal diet supplemented with 0.5% MMT, Cd-comtaminated basal diet (120 mg Cd/kg dry weight) and Cd-contaminated basal diet supplemented with 0.5% MMT, respectively. After 60 days, fish were sacrificed to measure malondialdehyde (MDA) content and antioxidative indices in liver and kidney. The results showed that the exposure of carp to dietary Cd caused decreases in glutathione peroxidase activity, catalase activity, superoxide dismutase activity, glutathione content and total antioxidant capacity level, while MMT supplemented in diet compensated Cd-induced decreases in above antioxidant indices to some extent in liver and kidney. As compared with the control group, increases in MDA content were observed in both measured tissues of carp exposed to dietary Cd, while MDA content decreased in carp exposed to Cd-contaminated basal diet supplemented with MMT in comparison with the Cd-contaminated group. It was suggested that MMT, when co-administered with Cd in diet, could alleviate dietary Cd-induced oxidative damage in liver and kidney of carp.

Distribution of trace metals and methylmercury in soft tissues of the freshwater eel Anguilla marmorata in Vietnam

This study investigated trace metals in water, sediment, and various organs of the mature eel Anguilla marmorata in the Ba River, Vietnam. The metal concentrations in water and sediment did not exceed the Vietnam water criteria and sediment background concentration, except for Mn and Pb in sediment. The results of metal analysis in eel specimens indicated that the liver and kidney were the dominant organs for almost all trace metals, whereas muscle tended to accumulate high levels of Hg and approximately 87.4-100% of Hg was methylmercury. A strong positive correlation between mercury levels in muscle and age were found, but there was no correlation between mercury and body size. Interestingly, a high concentration of Zn was found in the gonad and liver; this indicated that high levels of Zn in the liver might play a physiologically important role in the eel's biological mechanisms during gonadal maturation. Though almost none of the metal concentrations in the muscle exceeded the reference doses of the U.S. EPA, approximately 80% of eels from the river contained mercury exceeding the recommended levels (0.30 microg/g) of the U.S. EPA and might present a risk for human consumption.

Ultimobranchial gland of a freshwater teleost, Heteropneustes fossilis, in response to cadmium treatment

Heteropneustes fossilis were subjected to 288 mg/L (0.8 of 96 h LC(50)) and 72 mg/L (0.2 of 96 h LC(50)) of cadmium chloride for short-term and long-term experiments, respectively. After sacrificing the fish, the blood was collected on 24, 48, 72, and 96 h in short-term and after 7, 14, 21, and 28 days in long-term experiment and analyzed for plasma calcium levels. Also, ultimobranchial glands were fixed on these intervals. The plasma calcium levels of short-term cadmium-exposed fish remain unchanged after 24 h. The levels exhibit a progressive decrease from 48 h onwards. The fish exposed to cadmium for 7 days exhibit a decrease in the plasma calcium level. Thereafter, the levels progressively decrease till the end of the experiment (28 days). Up to 72 h exposure of the fish to cadmium, the ultimobranchial gland exhibits no histological change. After 96 h, a decrease in the staining response of the cytoplasm of ultimobranchial cells has been noticed. The nuclear volume of these cells records a slight decrease. Up to 14 days of cadmium exposure, there is no change in the histological structure of ultimobranchial gland. After 21 days following the exposure, the ultimobranchial cells exhibit a slight decrease in the staining response of the cytoplasm and the nuclear volume of these cells records a decrease. Following 28 days cadmium exposure the nuclear volume exhibits a further decrease, and degeneration and vacuolization sets in.

Accumulation of cadmium in the otoliths and tissues of juvenile pink snapper (Pagrus auratus Forster) following dietary and waterborne exposure

Laboratory experiments were conducted to examine if incorporation of Cd into the otoliths of juvenile pink snapper (Pagrus auratus Forster) was related to levels in the food or water. In the first experiment, fish were fed a regular diet (control group) or a Cd-contaminated diet (500mgCdkg(-1) or 1500mgCdkg(-1)) for 35days. In the second experiment, fish were exposed to waterborne Cd concentrations of <0.002microgL(-1) (control), 50microgL(-1), 100microgL(-1) and 150microgL(-1) for 35days. The sagittal otoliths were analysed using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Juvenile fish exposed to higher concentrations of waterborne or dietary Cd showed increased Cd levels in their otoliths. This study clearly demonstrated that both aqueous and dietary Cd exposures can result in Cd incorporation into the otoliths of pink snapper.

Cadmium accumulation and in vitro analysis of calcium and cadmium transport functions in the gastro-intestinal tract of trout following chronic dietary cadmium and calcium feeding

Juvenile rainbow trout (Oncorhynchus mykiss) were fed diets made from Lumbriculus variegatus containing environmentally relevant concentrations of Cd (approximately 0.2 and 12 microg g(-1) dry wt) and/or Ca (1, 10, 20 and 60 mg g(-1) dry wt) for 4 weeks. Ten fish per treatment were removed weekly for tissue metal burden analysis. In all portions of the gastro-intestinal tract (GIT) (stomach, anterior, mid, and posterior intestine), chronic exposure to elevated dietary Ca decreased Cd tissue accumulation to varying degrees. At week five, the GITs of the remaining fish were subjected to an in vitro gut sac technique. Pre-exposure to the different treatments affected unidirectional uptake and binding rates of Cd and Ca in different manners, dependent on the specific GIT section. Ca and Cd uptake rates were highly correlated within all sections of the GIT, and the loosely binding rate of Cd to the GIT surfaces predicted the rate of new Cd absorption. Overall, this study indicates that elevated dietary Ca is protective against Cd uptake from an environmentally relevant diet, and that Ca and Cd uptake may occur through both common and separate pathways in the GIT.

Dietary cadmium and benzo(a)pyrene increased intestinal metallothionein expression in the fish Fundulus heteroclitus

Fish were individually fed food pellets containing cadmium, benzo(a)pyrene, or a combination of the two, then analyzed for metallothionein mRNA expression in the intestine, liver, and gill using real-time RT-qPCR. An initial experiment using only cadmium showed that ingestion of pellets varied in individual fish, and estimates of cadmium dose from the numbers of ingested pellets indicated considerable individual variability in cadmium dose. Induction of intestinal metallothionein mRNA was apparent, however, and a linear dose-response relationship was observed for metallothionein expression and cadmium dose in the intestine, but not the other organs, which showed no induction. In a second experiment, the entire daily cadmium dose was provided in a single contaminated pellet that was consumed by all treated fish, effectively eliminating the effect of variable ingestion rates on dose, and the interaction between cadmium and benzo(a)pyrene was also investigated. The intestine was again the primary organ for metallothionein induction by cadmium. When benzo(a)pyrene was administered together with cadmium, induction of metallothionein was potentiated by the presence of benzo(a)pyrene, with the main effect seen in the intestine, where already high levels of induction by cadmium alone increased by 1.74-fold when benzo(a)pyrene was present.

In vitro examination of interactions between copper and zinc uptake via the gastrointestinal tract of the rainbow trout (Oncorhynchus mykiss)

An in vitro gut sac technique was used to investigate whether reciprocal inhibitory effects occurred between Cu and Zn uptake in the gastrointestinal tract of the rainbow trout and, if so, whether there was regional variation among the stomach, anterior intestine, mid intestine, and posterior intestine in the phenomena. Metal accumulation in surface mucus and in the mucosal epithelium and transport into the blood space were assayed using radiolabeled Cu or Zn at environmentally realistic concentrations of 50 micromol L(-1) in the luminal saline, with 10-fold higher levels of the other metal (nonradioactive) as a potential inhibitor. Zn transport rates were generally higher than Cu transport rates in all compartments except the stomach, where they were lower. High [Zn] reduced Cu transport into the blood space in the mid and posterior intestines by 67% and 33%, respectively, whereas high [Cu] reciprocally reduced Zn transport into the blood space in these same sections by 54% and 78%. No inhibitions occurred in either the anterior intestine or the stomach. In these segments, elevated concentrations of the other metal stimulated Cu and Zn transport into the blood space and/or the mucosal epithelium by 50-100%, possibly by displacement from intracellular binding sites, thereby raising local concentrations at other transport sites. None of the treatments affected metal accumulation in surface mucus. The results indicate that one or more shared high-affinity pathways (possibly DMT1) occur in the mid and posterior intestine, which transport both Cu and Zn. These pathways appear to be absent from the stomach and anterior intestine, where other transport mechanisms may occur.

Does dietary Ca protect against toxicity of a low dietborne Cd exposure to the rainbow trout?

We examined the toxicity of Cd, provided in a natural diet and at an environmentally relevant concentration ( approximately 12microgg(-1) dry wt.), to the juvenile rainbow trout (Oncorhynchus mykiss). In addition, we tested the protection by elevated dietary Ca against both the accumulation and toxicity of dietary Cd from this natural diet (background Ca approximately 1mgg(-1) dry wt.). Food pellets were made from blackworms (Lumbriculus variegatus), and spiked with Cd and either no additional Ca or elevated ( approximately 60mgg(-1) dry wt.) concentrations for each of the treatment diets. Survival was unaffected for trout fed diet with 12microgg(-1) dry wt. Cd for a month, but growth was potentially reduced. Tissue burden analysis revealed that the stomach, liver and kidney accumulated the most Cd, with concentrations progressively increasing in the liver and kidney over the whole exposure period. Cd concentrations in the plasma and red blood cells were unaffected by the different treatments, but subcellular fractionation analysis indicated that a higher concentration of Cd was associated with the metal-sensitive fractions of red blood cells of the fish that were exposed to the dietborne Cd. Dietary Cd exposure also caused potential toxicity to cells of the stomach in that they bound more Cd to heat-denaturable proteins. However, detoxification appeared to take place in the Cd-exposed fish because more Cd was bound to metallothionein-like proteins by week 4 of exposure. Elevated Ca in the Cd diet generally protected against accumulation and toxicity of dietborne Cd. The protection against Cd accumulation was almost complete at the gills, robust in the stomach and whole body (> or =50% reductions), but not significant in the liver, kidney, carcass, plasma, or red blood cells. Elevated dietary Ca also reduced Cd accumulation in the organelles of the fish stomach and red blood cells. In addition, dietborne Ca not only reduced the uptake of Cd by the cells, but also altered how the cells handled Cd intracellularly. In general, our results have demonstrated the need to use diets with natural compositions for dietary toxicity studies.

Trophic transfer of Cd from larval chironomids (Chironomus riparius) exposed via sediment or waterborne routes, to zebrafish (Danio rerio): tissue-specific and subcellular comparisons

Zebrafish were fed chironomid larvae (8% wet weight daily ration) for 7 days, followed by 3 days of gut clearance in a static-renewal system. Regardless of whether the chironomids had been loaded with Cd via a waterborne exposure or sediment exposure, they had similar subcellular distributions of Cd, with the largest areas of storage being metal rich granules (MRG)>organelles (ORG)>enzymes (ENZ) except that sediment-exposed chironomids had significantly more Cd in the metallothionein-like protein (MTLP) fraction, and significantly less Cd in the cellular debris (CD) fraction. When zebrafish fed sediment-exposed chironomids (153+/-11 microg Cd/g dry weight) were compared directly to zebrafish fed waterborne exposed chironomids (288+/-12microg Cd/g dry weight), identical whole-body Cd levels were observed, despite the difference in the concentration in the food source. Thus trophic transfer efficiency (TTE) of Cd was significantly greater from sediment-exposed chironomids (2.0+/-0.5%) than from waterborne-exposed chironomids (0.7+/-0.2%). Subsequent tests with waterborne exposed chironomids loaded to comparable Cd concentrations, as well as with Cd-spiked manufactured pellets, demonstrated that TTEs were concentration-independent. In all treatments, zebrafish exhibited similar subcellular storage of Cd, with the greatest uptake occurring in the ORG fraction followed by the ENZ fraction. However, neither trophically available metal (TAM) nor metabolically available fractions (MAF) were good predictors for the TTEs found in this study. Tissue Cd concentrations were highest in the kidney and gut tissue, then liver, but lower in the gill, and carcass. Overall, the gut and carcass contributed >/=71% to total body burdens on a mass-weighted basis. This study presents evidence that Cd may be acquired by fish from natural diets at levels of environmental relevance for contaminated sites, and that the exposure route of the prey influences the TTE.

In vitro characterization of cadmium and zinc uptake via the gastro-intestinal tract of the rainbow trout (Oncorhynchus mykiss): Interactive effects and the influence of calcium

An in vitro gut sac technique was employed to study whether Cd and Zn uptake mechanisms in the gastro-intestinal tract of the rainbow trout are similar to those at the gills, where both metals are taken up via the Ca transport pathway. Metal accumulation in surface mucus, in the mucosal epithelium, and transport into the blood space were assayed using radiolabelled Cd or Zn concentrations of 50micromolL(-1) in the luminal (internal) saline. Elevated luminal Ca (10 or 100mmolL(-1)versus 1mmolL(-1)) reduced Cd uptake into all three phases by approximately 60% in the stomach, but had no effect in the anterior, mid, or posterior intestine. This finding is in accordance with recent in vivo evidence that Ca is taken up mainly via the stomach, and that high [Ca] diets inhibit Cd accumulation from the food specifically in this section of the tract. In contrast, 10mmolL(-1) luminal Ca had no effect on Zn transport in any section, whereas 100mmolL(-1) Ca stimulated Zn uptake, by approximately threefold, into all three phases in the stomach only. There was no influence of elevated luminal Zn (10mmolL(-1)) on Cd uptake in the stomach or anterior intestine, or of high Cd (10mmolL(-1)) on Zn uptake in these sections. However, high [Zn] stimulated Cd transport into the blood space but inhibited accumulation in the mucosal epithelium and/or mucus-binding in the mid and posterior intestine, whereas high [Cd] exerted a reciprocal effect in the mid-intestine only. We conclude that Cd uptake occurs via an important Ca-sensitive mechanism in the stomach which is different from that at the gills, while Cd transport mechanisms in the intestine are not directly Ca-sensitive. Zn uptake does not appear to involve Ca uptake pathways, in contrast to the gills. These results are discussed in the context of other possible Cd and Zn transport pathways, and the emerging role of the stomach as an organ of divalent metal uptake.

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

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

Dietary tissue cadmium accumulation in an amazonian teleost (Tambaqui, Colossoma macropomum Cuvier, 1818)

Understanding the effects of metal contamination in the Amazon basin is important because of the potential impact on this region of high biodiversity. In addition, the significance of fish as the primary source of protein for the local human population (living either alongside the Amazon River or in the city of Manaus) highlights the need for information on the metal transfer through the food chain. Bioaccumulation of metals in fish can occur at significant rates through the dietary route, without necessarily resulting in death of the organism. The goal of this work was to expose an economic relevant species from the Amazon basin (tambaqui, Colossoma macropomum) to dietary cadmium (Cd) at concentrations of 0, 50, 100, 200, and 400 µg.g-1 dry food. Fish were sampled on days 15, 30, and 45 of the feeding trials. Tissues were collected for analysis of Cd concentration using graphite furnace atomic absorption spectrophotometry. Cd accumulation in the tissues occurred in the following order: kidney > liver > gills > muscle. Relative to other freshwater fish (e.g., rainbow trout, tilapia), tambaqui accumulated remarkably high levels of Cd in their tissues. Although Cd is known to affect Ca2+ homeostasis, no mortality or growth impairment occurred during feeding trials.

Interactions of waterborne and dietary cadmium on the expression of calcium transporters in the gills of rainbow trout: influence of dietary calcium supplementation

Recent studies have shown that dietary Ca(2+) supplementation strongly inhibits uptake of Ca(2+) and Cd at the fish gill. To better understand the influence of dietary Ca(2+) on branchial Ca(2+) transport, we examined the expression of two trout gill calcium transporters during waterborne and dietary Cd exposure, at two different levels of dietary Ca(2+). Quantitative polymerase chain reaction (PCR) was used to monitor epithelial calcium channel (ECaC) and sodium-calcium exchange (NCX) mRNA levels following 7-28 days of exposure to these treatments. In brief, juvenile rainbow trout (Oncorhynchus mykiss) were exposed to control, 3 microg/L waterborne Cd, 500 mg/kg dietary Cd, or a combined 3 microg/L waterborne plus 500 mg/kg dietary Cd exposure, supplemented with either 20 mg/g or 60 mg/g dietary calcium (Ca(2+)). Two-way analysis of variance was used to discern the main effects of Cd exposure and dietary Ca(2+) supplementation on ECaC and NCX mRNA levels. We found that dietary Ca(2+) supplementation decreased significantly ECaC mRNA expression on days 14 and 21. In comparison, NCX mRNA levels were not influenced by dietary Ca(2+) supplementation, but rather were significantly inhibited in the combined waterborne and dietary Cd exposure on day 7 alone. Statistical analysis found no interactive effects between Cd exposure and dietary Ca(2+) exposure at any time point, except for day 28. This study provides evidence of the importance of nutritional status on the transcriptional regulation of ion transport at the fish gill. We discuss the importance of diet and nutritional status to the development of new regulatory approaches, such as the biotic ligand model, which currently do not account for the significance of diet on metal bioavailability in aquatic organisms.

Branchial cadmium and copper binding and intestinal cadmium uptake in wild yellow perch (Perca flavescens) from clean and metal-contaminated lakes

Branchial binding kinetics and gastro-intestinal uptake of copper and cadmium where examined in yellow perch (Perca flavescens) from a metal-contaminated lake (Hannah Lake, Sudbury, Ontario, Canada) and an uncontaminated lake (James Lake, North Bay, Ontario, Canada). An in vivo approach was taken for gill binding comparisons while an in vitro gut binding assay was employed for gastro-intestinal tract (GIT) uptake analysis. By investigating metal uptake at the gill and the gut we cover the two main routes of metal entry into fish. Comparisons of water and sediment chemistries, metal burdens in benthic invertebrate, and metal burdens in the livers of perch from the two study lakes clearly show that yellow perch from Hannah L. are chronically exposed to a highly metal-contaminated environment compared to a reference lake. We found that metal-contaminated yellow perch showed no significant difference in gill Cd binding compared to reference fish, but they did show significant decreases in new Cd binding and absorption in their GITs. The results show that gill Cd binding may involve low-capacity, high-affinity binding sites, while gastro-intestinal Cd uptake involves binding sites that are high-capacity, low-affinity. From this we infer that Cd may be more critically controlled at the gut rather than gills. Significant differences in branchial Cu binding (increased binding) were observed in metal-contaminated yellow perch. We suggest that chronic waterborne exposure to Cu (and/or other metals) may be the dominant influence in gill Cu binding rather than chronic exposure to high Cu diets. We give supporting evidence that Cd is taken up in the GIT, at least in part, by a similar pathway as Ca(2+), principally that elevated dietary Ca(2+) reduces Cd binding and uptake. Overall our study reveals that metal pre-exposure via water and diet can alter uptake kinetics of Cu and Cd at the gill and/or the gut.

In vitro analysis of the bioavailability of six metals via the gastro-intestinal tract of the rainbow trout (Oncorhynchus mykiss)

An in vitro gut sac technique was used to compare the uptake rates of essential (copper, zinc and nickel) and non-essential metals (silver, cadmium and lead) at 50 micromol L(-1) each (a typical nutritive level in solution in chyme) in the luminal saline in four sections of the gastro-intestinal tract (stomach, anterior, mid and posterior intestines) of the freshwater rainbow trout. Cu, Zn, Cd and Ag exhibited similar regional patterns: on an area-specific basis, uptake rates for these metals were highest in the anterior intestine, lowest in the stomach, and approximately equal in the mid and posterior intestinal segments. When these rates were converted to a whole animal basis, the predominance of the anterior intestine increased because of its greater area, while the contribution of the stomach rose slightly to approach those of the mid and posterior intestines. However, for Pb and Ni, area-specific and whole organism transport rates were greatest in the mid (Pb) and posterior (Ni) intestines. Surprisingly, total transport rates did not differ appreciably among the essential and non-essential metals, varying only from 0.025 (Ag) to 0.050 nmol g(-1)h(-1) (Ni), suggesting that a single rate constant can be applied for risk assessment purposes. These rates were generally comparable to previously reported uptake rates from waterborne exposures conducted at concentrations 1-4 orders of magnitude lower, indicating that both routes are likely important, and that gut transporters operate with much lower affinity than gill transporters. Except for Ni, more metal was bound to mucus and/or trapped in the mucosal epithelium than was transported into the blood space in every compartment except the anterior intestine, where net transport predominated. Overall, mucus binding was a significant predictor of net transport rate for every metal except Cd, and the strongest relationship was seen for Pb.

Renal function in the freshwater rainbow trout after dietary cadmium acclimation and waterborne cadmium challenge

Renal function was examined in adult rainbow trout (Oncorhynchus mykiss) after chronic exposure to a sublethal level of dietary Cd (500 mg/kg diet) for 52 d and during a subsequent challenge to waterborne Cd (10 microg/L) for 72 h. Dietary Cd had no major effects on UFR (urine flow rate) and GFR (glomerular filtration rate) but caused increased renal excretion of glucose, protein, and major ions (Mg(2+), Zn(2+), K(+), Na(+), Cl(-) but Ca(2+)). However, dietary Cd did not affect any plasma ions except Na(+) which was significantly elevated in the Cd-acclimated trout. Plasma glucose and ammonia levels fell by 25% and 36% respectively, but neither plasma nor urine urea was affected in Cd-acclimated fish. Dietary Cd exposure resulted in a remarkable increase of Cd load in the plasma (48-fold, approximately 22 ng/mL) and urine (60-fold, 8.9 ng/mL), but Cd excretion via the kidney was negligible on a mass-balance basis. Clearance ratio analysis indicates that all ions, Cd, and metabolites were reabsorbed strongly (58-100%) in both naïve and dietary Cd exposed fish, except ammonia which was secreted in both groups. Mg(2+), Na(+), Cl(-) and K(+) reabsorption decreased significantly (3-15%) in the Cd-exposed fish relative to the control. Following waterborne Cd challenge, GFR and UFR were affected transiently, and only Mg(2+) and protein excretion remained elevated with no recovery with time in Cd-acclimated trout. Urinary Ca(2+) and Zn(2+) excretion rates dropped with an indication of renal compensation towards plasma declines of both ions. Cadmium challenge did not cause any notable effects on urinary excretion rates of metabolites. However, a significant decrease in Mg(2+) reabsorption but an increase in total ammonia secretion was observed in the Cd-acclimated fish. The study suggests that dietary Cd acclimation involves physiological costs in terms of renal dysfunction and elevated urinary losses.

Assimilation efficiencies of Cd and Zn in the common carp (Cyprinus carpio): effects of metal concentration, temperature and prey type

The impact of several factors on the assimilation efficiency (AE) of Cd and Zn from food in the common carp (Cyprinus carpio) was studied. Tested prey species were midge larvae (Chironomus riparius), zebra mussels (Dreissena polymorpha) and oligochaetes (Tubifex tubifex). The Cd load of the larvae did not affect the Cd AE in the carp. The Zn AE however, was negatively related to the Zn load of the prey. Food quantity and starvation of the carp did not significantly affect the Cd AE. For Zn, a significant decrease in AE was found when carp were fed ad libitum. Decreasing the temperature from 25 degrees C to 15 degrees C did not influence the Cd AE, while for Zn a significant decrease of the AE was measured. Carp assimilated Cd from both zebra mussels and oligochaetes with a significantly lower efficiency in comparison to the midge larvae, although Zn AEs was prey independent.

Effects of Ca2+ or Na+ on metallothionein expression in tilapia larvae (Oreochromis mossambicus) exposed to cadmium or copper

The objectives of this study were to try to determine the reasons of the external Ca(2+) and Na(+) enhancement of Cd(2+) and Cu(2+) resistance in fish. Tilapia larvae at 3 days posthatch were exposed to (A) 0 (control), 40 microg/L Cd(2+), 40 microg/L Cd(2+) + 2 mM Ca(2+) (Cd/hyper-Ca), and 2 mM Ca(2+) or (B) 0 (control), 75 microg/L Cu(2+), 75 microg/L Cu(2+) + 0.52 mM Na(+) (Cu/hyper-Na), and 0.52 mM Na(+). After 48 hours, results indicated that (1) Cd/hyper-Ca and Cu/hyper-Na treatments showed decreased growth inhibition induced by the metals; (2) metal accumulation in Cd/hyper-Ca-treated larvae was lower compared with those exposed only to Cd; and (3) metallothionein (MT) expression was significantly higher in Cu/hyper-Na-treated larvae than in the group treated with Cu only. Taking all of this into account, either supplementary Ca(2+) or Na(+) in ambient water may help fish to maintain Ca(2+) or Na(+) homeostasis, which could decrease metal accumulation and its detrimental effects. Consequently, the fish increase MT expression and retard the growth inhibition caused by metals.