Metallothionein and cortisol receptor expression in gills of Atlantic salmon, Salmo salar, exposed to dietary cadmium

The Cortisol Levels, Histology, and Fine Structure of Various Tissues of Fish Gambusia affinis (Baird and Girard, 1853) after Exposure to Lead

Background

Aquatic organisms demonstrate a high vulnerability to mortality when exposed to Pb, even at low concentrations. The objective of this investigation is to ascertain the histopathological alterations and cortisol concentrations in diverse tissues of Gambusia affinis, with a specific focus on the eggs and larvae, following exposure to varying concentrations of PbCl2.

Methods

Adult specimens of G. affinis measuring 5-6 cm in length were obtained from a commercial fish breeding facility. A total of 8 fish with a 1 : 1 ratio of 4 pairs of broodstock were placed in an 8-liter aquarium. Following the adaptation phase, the broodstock underwent a spawning process that lasted for a duration of 7 days. Throughout the spawning process, assessments were conducted on the progression of the abdominal growth of the broodstock. Eggs ready to hatch and Gambusia larvae were taken and exposed to 0.1 mg/L PbCl2, 1 mg/L PbCl2, and control (without PbCl2) for 24 hours, with three replications. At the end of the experiment, histopathological analysis was conducted using the hematoxylin Ehrlich-eosin staining method and scanning electron microscopic (SEM) observation. The levels of Pb in gills were determined by employing atomic absorption spectrophotometer. The cortisol concentration in organ samples of fish was determined through the utilization of a cortisol ELISA Kit.

Results

The findings of this investigation demonstrated an important bioaccumulation occurrence of Pb within the gills of Gambusia fish that were specifically subjected to 0.1 and 1 mg/L PbCl2. The histological structures of eggs and larvae that were subjected to PbCl2 exhibited impairment in comparison to the control group. The present study observed a significant elevation in cortisol levels among fish specimens that were subjected to PbCl2 exposure.

Conclusions

The findings of this investigation suggest that the occurrence of Pb is linked to a rise in cortisol concentrations in various organs of G. affinis larvae. Furthermore, the research indicates that the exposure to Pb has a notable impact on the histological alterations in the eggs and larvae of Gambusia fish, implying that they are undergoing stress as a result of the Pb exposure.

Cadmium Accumulation and Kinetics in Solea senegalensis Tissues under Dietary and Water Exposure and the Link to Human Health

Bioaccumulation of cadmium was assessed in different tissues of the benthic fish Solea senegalensis. Juvenile Senegalese soles were simultaneously exposed to cadmium-contaminated diet (Hediste diversicolor) and water during 14 days and allowed to depurate for another 14 days. Cadmium content was measured in muscle, gills, liver and intestine, with recorded values increasing in these tissues in this same order. Muscle showed a considerably lower cadmium accumulation after 14 days of uptake. Cadmium kinetics in juvenile Senegalese soles revealed that the highest uptake flux of this metal occurred in the intestine. Cadmium depuration from the liver was not detected, which suggests the existence of a storage compartment for this metal in Solea senegalensis during uptake and depuration. Comparisons between maximum acceptable values for cadmium in the muscle, the Target Hazard Quotient and the Estimated Weekly Intake, indicated that acceptable limits were not exceeded, and the muscle of juvenile Senegalese soles could be considered safe for human consumption.

Biochemical profile and gene expression of Clarias gariepinus as a signature of heavy metal stress

Heavy metals have been found in increasing concentrations in the aquatic environment. Fishes exposed to such metals have altered gene expression, serum profiles, tissue histology and bioindices that serve as overall health biomarkers. The heavy metals (Ni, Cd, and Cr) accumulated in water and fish tissues, were beyond the permissible limits defined by the Central Pollution Control Board/World Health Organization. Metallothionein (MT) and glutathione peroxidase (GPX) genes expression patterns highlighted the metal-specific exposure of fish. An increased fold change of genes against beta-actin serves as a potential feature for toxicity. Metal toxicity is also reflected by an increased level of digestive enzymes (amylase and lipase) in the serum and alterations in values of reproductive hormones (11-Ketotestosterone and progesterone). Total serum bilirubin attribute to the liver and biliary tract disease in fishes. Histopathological studies show cellular degeneration, breakage, vacuolization signifying the chronic stress.

Morphofunctional Alterations in Zebrafish (Danio rerio) Gills after Exposure to Mercury Chloride

Mercury (Hg) is a global pollutant that may exert its toxic effects on living organisms and is found in both aquatic and terrestrial ecosystems in three chemical forms; elemental, organic, and inorganic. The inorganic form (iHg) tends to predominantly accumulate in aquatic environments. The gill apparatus is a very dynamic organ that plays a fundamental role in gas exchange, osmoregulation, acid-base regulation, detoxification, and excretion, and the gills are the primary route of waterborne iHg entrance in fish. In the present work we investigated the morphofunctional and ultrastructural effects in Danio rerio gills after 96 h exposure to two low HgCl₂ concentrations (7.7 and 38.5 µg/L). Our results clearly demonstrated that a short-term exposure to low concentrations of mercury chloride resulted in gill morphology alterations and in the modifications of both Na+/K⁺-ATPase and metallothioneins (MTs) expression pattern. The main morphological effects recorded in this work were represented by hyperplasia and ectopia of chloride cells (CCs), lamellar fusion, increased mucous secretion, alteration of pavement cells (PVCs), detachment of the secondary epithelium, pillar cell degeneration, degeneration, and apoptosis. Trough immunohistochemistry and real-time PCR analysis also showed a dose-related modulation of Na⁺/K⁺-ATPase and MTs.

Toxic effects of two sources of dietborne cadmium on the juvenile cobia, Rachycentron canadum L. and tissue-specific accumulation of related minerals

In the present study, juvenile cobia, Rachycentron canadum L. were fed diets contaminated by two different sources of cadmium: squid viscera meal (SVM-Cd, organic form) and cadmium chloride (CdCl2-Cd, inorganic form). The Cd concentrations in fish diet were approximate 3.0, 5.0 and 10.0mg Cd kg(-1) for both inorganic and organic forms. In the control diet (0.312mg Cd kg(-1) diet, Cd mainly come from fish meal), no cadmium was added. The experiment lasted for 16 weeks and a statistically significant inverse relationship was observed between specific growth rate (SGR) and the concentration of dietary Cd. The SGR of cobia fed a diet with SVM-Cd increased at the lowest doses and decreased with the increasing level of dietary SVM. Fish fed diet contaminated SVM-Cd had significantly higher SGR than those fed diets contaminated CdCl2-Cd among the high Cd level diets treatments. The dietary Cd levels also significantly affected the survival rate of the fish. Among the hematological characteristics and plasma constituents, glutamic-pyruvic transaminase activities and alkaline phosphatase activities in serum and liver increased and hepatic superoxide dismutase activity decreased with the increasing dietary Cd levels. The cobia fed diet contaminated by high level of CdCl2-Cd had significantly higher ALP activity than cobia fed diet contaminated by high level of SVM-Cd. The results from these studies indicate no differences in toxicity response to dietborne SVM-Cd and CdCl2-Cd at a low level of Cd. However, at a higher level, cobia was more sensitive to dietborne CdCl2-Cd than SVM-Cd. Based on quadratic regression of SGR, The Cd concentrations was 3.617mg kg(-1) in the optimal diet, Cd source was SVM (126mg Cd kg(-1) in SVM) which stimulate the growth of cobia and the added level was determined to be 26.7g kg(-1) diet in the present study. Cd accumulations in the kidney of cobia fed both types of Cd were higher than other tissues, and the order of Cd accumulation in tissues were kidney>liver>intestine>gill>muscle. Iron accumulation in liver and kidney and calcium accumulation in vertebra and scale were also significantly affected by dietary Cd levels.

Cadmium Chloride Toxicity Revisited: Effect on Certain Andrological, Endocrinological and Biochemical Parameters of Adult Male Rabbits

The present study was devised to assess the effects of cadmium chloride (CdCl2) administration on certain andrological, endocrinological and biochemical alterations in adult male rabbits (n=24). The animals were assigned to control (n=8) and experimental (n=16) group. Experimental group was orally administered with 1.5 mg/kg body weight of CdCl2. The trials were carried out for a total of 5 weeks and blood sampling was carried out on weekly basis. A gradual decrease was noticed for body weight in the experimental group from week 1 to 5, being significantly lower in week 4 and 5 (P<0.05). A similar decremented trend was noticed for serum testosterone level being significantly lower in experimental group in week 4 and 5 (P<0.001). Significantly lower values were noticed for prolactin in experimental group in week 4 and 5 (P<0.05), than in the control. On the contrary, serum cortisol level showed a gradual increase in experimental group, from week 1 to 5, being significantly higher in week 4 and 5 (P<0.05). Regarding the biochemical attributes, all the parameters under study revealed a gradually ascending trend. Statistical significance was, however, achieved in varying weeks and at varying levels. The total protein and albumin were significantly higher in week 4 and 5 (P<0.01); alanine aminotransferase in week 2 (P<0.01), 3 (P<0.001), 4 (P<0.01) and 5 (P<0.001); aspartate aminotransferase in week 1, 2, 3, 4 and 5 (P<0.01); and alkaline phosphatase in week 1, 2 (P<0.01), 3, 4 and 5 (P<0.0001), respectively. Overall mortality rate in experimental group was 68.75 (11/16). In a nutshell, Cd exposure results in adverse effects on all physiological parameters of body and may lead to lethal consequences.

Understanding the adaptive response in vertebrates: the phenomenon of ease and ease response during post-stress acclimation

Vertebrates have evolved mechanisms to perceive stressors that arise either from their body or from the environment. Consequently, a state of stress and stress response occur in fish which is characterized by a disturbed physiological homeostasis. The pattern of stress response becomes complex as a result of neuroendocrine involvement and shows varied magnitudes in fishes depending on the nature and the severity of stressors. The integrated and compensatory physiological modifications in fishes during their early phase of adaptive response favor them to accommodate the imposed stressor through the process of stress acclimation. In contrast, with the direction of neuroendocrine signals, a phase of recovery often called post-stress acclimation occurs if the animal gets away from the stressor exposure. During this late phase of adaptive response, physiological modifications operate in favor of the animal that reduces the magnitude of stress response and finally to a phase of normality as animals possess the urge to correct its disrupted homeostasis. The phenomenon of ease and its response thus reduces the allostatic load, resets the homeostatic state through physiologic processes and corrects the stress-induced homeostatic disturbance with the aid of neuroendocrine signals. Ample evidences are now available to support this novel concept of ease and ease response where mitigation of the intensity of stress response occurs physiologically. Treatment of fish with melatonin or serotonin precursor tryptophan can modify the magnitude of stress response as evident in the pattern of tested physiological indices. In addition to cortisol, thyroid hormone as a major stress modifier hormone is involved in the regulation of ease response in fish probably due to the mechanisms involving inter-hormonal interference. Understanding the mechanisms of adaptive responses in vertebrates thus warranties more studies on the physiology of ease and its response.

Carbaryl exposure and recovery modify the interrenal and thyroidal activities and the mitochondria-rich cell function in the climbing perch Anabas testudineus Bloch

We examined the effects of carbaryl (1-naphthyl methylcarbamate; sevin), a carbamate pesticide, on interrenal and thyroid activities and mitochondrial rich (MR) cell function in climbing perch to understand the physiological basis of toxicity acclimation in this fish to the chemical stressor. Carbaryl exposure (5-20 mg L(-1)) for 48 h increased cortisol and glucose, but decreased the T(3) level without affecting T(4) concentration in the plasma. These responses of the carbaryl-exposed fish were nullified and a rise in plasma T(4) occurred in these fish when they were kept for 96 h recovery in clean water. A tight plasma mineral control was indicated in the carbaryl-exposed fish as reflected by the unchanged plasma Na, K, Ca and inorganic phosphate levels. The ouabain-sensitive Na(+), K(+)-ATPase activity showed an increase in the gills but the intestinal and renal tissues showed little response to carbaryl treatment. However, substantial increases in the intestinal and renal Na(+), K(+)-ATPase activities occurred in the recovery fish. The MR cells in the branchial epithelia showed a strong Na(+), K(+)-ATPase immunoreactivity to carbaryl treatment indicating an activated MR cell function. The numerical MR cell density remained unchanged, but stretching of secondary gill lamellae as part of gill remodeling occurred during carbaryl exposure. The increased surface of these lamellae with abundant MR cells as a result of its migration into the lamellar surface points to marked structural and functional modifications of these cells in the carbaryl-treated fish which is likely to a target for carbaryl action. The rise in plasma T(4) and the restoration of normal branchial epithelia in the recovery fish indicate a thyroidal involvement in the recovery response and survival. Our data thus provide evidence that carbaryl exposure and its recovery evoke interrenal and thyroid disruption in this fish leading to a modified osmotic response including an altered MR cell function.

A novel report of metallothioneins in fish bile: SDS-PAGE analysis, spectrophotometry quantification and metal speciation characterization by liquid chromatography coupled to ICP-MS

Metallothioneins (MT) are a validated biomarker for metal exposure. In fish they are usually determined in the liver, while some studies have observed MT in kidney, muscle and gills. There are, however, no reports on MT in fish bile. This study aimed to verify if these proteins are present in fish bile, if they can be used as biomarkers for metal exposure and to characterize the metal speciation present in the different species. Three independent methods to verify MT presence in fish bile were conducted: 1D/2D gel electrophoresis, spectrophotometric analyses and SEC-HPLC-ICP-MS. Results show that all methods verified the presence of these proteins in fish bile, while SEC-HPLC-ICP-MS also characterized also characterized metals responsible for the contamination of the studied sites. Quantification was successfully conducted by two methods, densitometry (1D electrophoresis) and spectrophotometry, and the data indicates that bile MTs follow the same trend as in liver. Therefore, Biliary MT show the potential to be used the same way as MT from other matrices in metal exposure studies, with the advantage of being a simpler matrix and showing the possibility of not sacrificing the animals, as chronic duct cannulation is available.

The interruption of thyroid and interrenal and the inter-hormonal interference in fish: does it promote physiologic adaptation or maladaptation?

Endocrines, the chief components of chemical centers which produce hormones in tune with intrinsic and extrinsic clues, create a chemical bridge between the organism and the environment. In fishes also hormones integrate and modulate many physiologic functions and its synthesis, release, biological actions and metabolic clearance are well regulated. Consequently, thyroid hormones (THs) and cortisol, the products of thyroid and interrenal axes, have been identified for their common integrative actions on metabolic and osmotic functions in fish. On the other hand, many anthropogenic chemical substances, popularly known as endocrine disrupting chemicals, have been shown to disrupt the hormone-receptor signaling pathways in a number fish species. These chemicals which are known for their ability to induce endocrine disruption particularly on thyroid and interrenals can cause malfunction or maladaptation of many vital processes which are involved in the development, growth and reproduction in fish. On the contrary, evidence is presented that the endocrine interrupting agents (EIAs) can cause interruption of thyroid and interrenals, resulting in physiologic compensatory mechanisms which can be adaptive, though such hormonal interactions are less recognized in fishes. The EIAs of physical, chemical and biological origins can specifically interrupt and modify the hormonal interactions between THs and cortisol, resulting in specific patterns of inter-hormonal interference. The physiologic analysis of these inter-hormonal interruptions during acclimation and post-acclimation to intrinsic or extrinsic EIAs reveals that combinations of anti-hormonal, pro-hormonal or stati-hormonal interference may help the fish to fine-tune their metabolic and osmotic performances as part of physiologic adaptation. This novel hypothesis on the phenomenon of inter-hormonal interference and its consequent physiologic interference during thyroid and interrenal interruption thus forms the basis of physiologic acclimation. This interfering action of TH and cortisol during hormonal interruption may subsequently promote ecological adaptation in fish as these physiologic processes ultimately favor them to survive in their hostile environment.

Changes of glycogen metabolism in the gills and hepatic tissue of tilapia (Oreochromis mossambicus) during short-term Cd exposure

The aim of the study was to test the hypothesis that the mechanism of glycogen metabolism has taken place in gills rather than in liver during Cd exposure. Male tilapia were exposed to 44.45 μM ambient Cd for 12h, and we found blood glucose significantly increased, however, lactate levels showed no significant changes. The glycogen phosphorylase (GP) activity increased immediately after 0.75 to 3h of Cd exposure in the gills, and after 1 to 6h in the liver, respectively. In addition, the glycogen level depleted faster in the gills than in the liver. Plasma cortisol level increased from 0.25 to 1h and recovered after 3h, while the glucagon did not significantly change during Cd exposure. Glucocorticoid receptor (GR) mRNA expression decreased after 0.75 h in the gills, while it significantly increased after 6h in the liver. Ca(2+), Na(+), Cl(-), and K(+) significantly decreased upon Cd exposure within 6h following Cd-induced toxic stress. We suggested that the cortisol is the spontaneous stimulation of glycogen metabolism in the gills, and it triggers a subsequent energy supply later in the liver. Taken together, the profile of glycogen metabolism between gills and liver during Cd-exposure stress provide good support to our hypothesis.

The role of thyroid hormones in stress response of fish

Thyroxine (T(4)) and triiodothyronine (T(3)), the principal thyroid hormones (THs) secreted from the hypothalamic-pituitary-thyroid (HPT) axis, produce a plethora of physiologic actions in fish. The diverse actions of THs in fishes are primarily due to the sensitivity of thyroid axis to many physical, chemical and biological factors of both intrinsic and extrinsic origins. The regulation of THs homeostasis becomes more complex due to extrathyroidal deiodination pathways by which the delivery of biologically active T(3) to target cells has been controlled. As primary stress hormones and the end products of hypothalamic-pituitary-interrenal (HPI) and brain-sympathetic-chromaffin (BSC) axes, cortisol and adrenaline exert its actions on its target tissues where it promote and integrate osmotic and metabolic competence. Despite possessing specific osmoregulatory and metabolic actions at cellular and whole-body levels, THs may fine-tune these processes in accordance with the actions of hormones like cortisol and adrenaline. Evidences are presented that THs can modify the pattern and magnitude of stress response in fishes as it modifies either its own actions or the actions of stress hormones. In addition, multiple lines of evidence indicate that hypothalamic and pituitary hormones of thyroid and interrenal axes can interact with each other which in turn may regulate THs/cortisol-mediated actions. Even though it is hard to define these interactions, the magnitude of stress response in fish has been shown to be modified by the changes in the status of THs, pointing to its functional relationship with endocrine stress axes particularly with the interrenal axis. The fine-tuned mechanism that operates in fish during stressor-challenge drives the THs to play both fundamental and modulator roles in stress response by controlling osmoregulation and metabolic regulation. A major role of THs in stress response is thus evident in fish.

Assessment of tissue-specific accumulation and effects of cadmium in a marine fish fed contaminated commercially produced diet

Commercially produced fish diet is now widely used in fish farming but it often contains elevated levels of cadmium (Cd). However, the adverse effects on fish are poorly understood. In this study, farm-raised marine grunts, Terapon jarbua, were fed Cd-contaminated diet or exposed to waterborne Cd for 4 weeks. Tissue-specific Cd bioaccumulation and its effects were subsequently examined. We found that Cd was accumulated in different fish tissues (digestive tracts, gills or livers). At the end of the exposure, Cd accumulation peaked in the fishes' livers (5.0-6.3microgg(-1)), followed by the digestive tracts (0.83-3.16microgg(-1)) and gills (0.27-2.74microgg(-1)). Endpoints such as the survival rate, specific growth rate, condition factor, and superoxide dismutase activity were not significantly affected by Cd exposure. In contrast, metallothionein (MT) induction and subcellular Cd distribution indicated that there were possible sublethal effects of Cd exposure. MT was induced in response to Cd accumulation, but it returned to the control levels after a longer exposure period, except for hepatic MT induction resulting from waterborne or low dietary Cd exposure. The Cd percentage in the metallothionein-like protein (MTLP) fraction increased over exposure time, and it accounted for more than 57% Cd in the fishes' livers and 80% Cd in their digestive tracts by the end of the exposure period. Overall, although Cd in commercial fish diet did not have significant lethality to T. jarbua, sensitive responses such as hepatic MT induction and subcellular Cd distribution revealed that the Cd-induced storage and detoxification in T. jarbua may increase fish's tolerance to toxic metals.

Gene structure and expression of metallothionein during metal exposures in Hemibarbus mylodon

Metallothionein gene was characterized in Hemibarbus mylodon, an endangered fish species. H. mylodon MT shared a high homology with other vertebrate MTs, including (1) tripartite exon/intron structure, (2) typical regulatory elements such as MREs and GC boxes in the 5'-flanking region, and (3) high proportion of Cysteines (33.3%) in its amino acid sequence. MT mRNA was ubiquitously detected in various tissues. Basal level of MT mRNA was the highest in ovary while the lowest in heart. Transcription of MT was highly inducible by exposures to waterborne cadmium (0.1-10 microM), copper (2-10 microM) or zinc (2-10 microM), based on real-time RT-PCR. Cadmium was more potent for the stimulation of MT transcripts than copper and zinc. Liver was more responsive to heavy metals than kidney and gill. In overall, the transcriptional activation of MT gene by metal exposures followed a dose- and/or time-dependent fashion.

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.

Hepatic metallothionein and total oxyradical scavenging capacity in Atlantic cod Gadus morhua caged in open sea contamination gradients

Biological effects monitoring has seldom been undertaken in offshore pelagic environments. Cages containing hatchery-reared Atlantic cod Gadus morhua were deployed on expected contamination gradients, along a transect from the River Elbe in the German Bight, and in the vicinity of an oil field in the North Sea (Statfjord). Six weeks later, the cod were retrieved and samples taken for a range of biological effects techniques. In this study, metallothionein (MT) and total oxyradical scavenging capacity (TOSC) were measured in liver samples from the caged cod, together with metals (as a measure of bioaccumulation). Both MT and TOSC were highest in cod from the German Bight. In the Statfjord samples MT and TOSC decreased with distance from the oil platform indicating induction in response to anthropogenic sources. The bioavailability of metals appears to be a major factor in MT synthesis, and the measurement of MT and associated metals is shown to be a useful tool for biological exposure and effects monitoring in pelagic systems. There also appears to be a strong linkage between MT and TOSC levels, indicating overlapping capabilities as stress biomarkers. Results suggest that in addition to its role as a specific indicator of metal exposure, MT in cod could act as a more general biomarker of oxidative stress under certain conditions.

Toxicological stress response and cadmium distribution in hybrid tilapia (Oreochromis sp.) upon cadmium exposure

Adult tilapia were exposed to 0 (control) and 4.45 microM Cd for 0 h, 5 h, 5 days, and 15 days, and the physiological responses of fish were described. The physiological responses were first expressed in gill tissue, in which mucus cells secretion increased, Cd accumulated, cortisol secretion was significantly higher, but serum ACH(50) activity (alternative complement hemolytic assay) was significantly lower than in controlled fish. After 5 days of Cd exposure, the ACH(50) activity showed a greater decrease, but lysozyme and cortisol contents showed significant increases over the control. Cd levels significantly increased in intestines, liver, and kidneys, and a significant induction of metallothionein (MT) protein in hepatic tissue was noted. Finally, the Cd accumulation rate still showed significant increases in these organs. However, the MT content was similar at 5 days and at 15 days after Cd exposure, and the cortisol contents had recovered to the pre-exposure level. In addition, Cd accumulation in muscle was higher after Cd exposure than in controls (t-test, p<0.05). Our results demonstrate (1) that tilapia readily regulate their physiological parameters in order to acclimate to a sublethal Cd environment; (2) these changes of physiological parameters may be related with a succession of cortisol levels following Cd exposure; (3) increasing rate of hepatic MT contents and Cd accumulation rate didn't appear identical after 5-15 days of Cd exposure. This was confirmed that hepatic MT was not a good indicator for Cd levels in tilapia.

Quantitative changes in metallothionein expression in target cell-types in the gills of turbot (Scophthalmus maximus) exposed to Cd, Cu, Zn and after a depuration treatment

Turbot (Scophthalmus maximus) were exposed to two sublethal concentrations (1 and 10 mg metal/l) of cadmium (8.9 and 89 microM Cd), copper (15.26 and 152.6 microM Cu) and zinc (15.3 and 153 microM Zn) for 7 days, and afterwards were maintained depurating for 14 days. Immunoreactive metallothioneins (irMTs) and metal ions were localized in the branchial epithelium by immunohistochemistry (using an anti-Cod MT antibody) and autometallography (AMG), respectively. Metal ions were demonstrated by AMG as black silver deposits (BSD), mainly in mucocytes (MC) and to a lesser extent in the other branchial cell-types (respiratory cells (RC), chloride cells (CC) and basal layer cells (BLC)). Irrespective of the metal supplied, BSD were rapidly visualized in MC after 1 h of exposure. This accumulation did not increase with increasing exposure time and concentration. Metallothionein expression was mainly observed in mature CC in the interlamellar space for all exposure conditions and it was shown that all mature cells express the same amount of irMT. The number of CC exhibiting irMT in metal-exposed turbots increased following short exposure times (1 h-1 day) in the filament epithelium and following longer exposure times (1-7 days) in the secondary lamellae. Total levels of irMT in the gills (quantified by image analysis and densitometry) increased significantly in metal-exposed turbot and were related to increased exposure times. It can be concluded that the total content of irMT in the gills of metal-exposed turbot is governed by changes in the number of mature CC expressing the protein. The quantification of total irMT in branchial CC can be considered as a reliable biomarker of metal exposure since reflects changes in metal bioavailability. This approach based on cell-selective immunohistochemistry can be simplified by only quantifying the number of mature CC. In addition, the dramatic increase of CC in the gills that produces epithelial thickening of the FE enhances migration of CC up to the edge of the SL and provokes the hypertrophy and fusion of secondary lamellae can be considered as unspecific biomarkers of effect indicating disturbed health in turbot.

Cellular biomarkers of exposure and biological effect in hepatocytes of turbot (Scophthalmus maximus) exposed to Cd, Cu and Zn and after depuration

Cellular biomarkers of exposure and biological effects were measured in hepatocytes of turbot exposed to either Cd, Cu or Zn at concentrations of 1 and 10 mg/l seawater for 7 days and after depuration for 14 days. Metal content in hepatocyte lysosomes was determined by image analysis after autometallography (AMG) as volume density of autometallographed black silver deposits (Vv(BSD)). Metallothionein (MT) levels were quantified on liver sections by microdensitometry after immunohistochemical staining with a polyclonal anti cod-MT antibody (MT-OD), and in the cytosolic fraction of hepatocytes by difference pulse polarography (MT-DPP). Lysosomal structural changes (lysosomal volume, surface and numerical densities--Vv(LYS), Sv(LYS) and Nv(LYS-), and surface-to-volume ratio S/V(Lys)) were quantified by image analysis after demonstration of beta-glucuronidase activity on liver cryotome sections. Vacuolisation produced by metal-exposure in hepatocytes was quantified by stereology as volume density of vacuoles (Vv(VAC)). Exposure time and metal concentrations significantly affected Vv(BSD) in lysosomes, MT levels and the degree of vacuolisation after 1 h and 1 day exposure to the three metals. The highest Vv(BSD), MT and Vv(VAC) values were recorded after 7 days exposure in all cases. MT-OD and MT-DPP were significantly correlated with Vv(BSD). Vv(LYS) in hepatocytes increased significantly after exposure to the metals. Exposure biomarkers returned to control values after depuration with the exception of those turbots that had been exposed to 10 mg Cd/l. Alike, Vv(LYS) and Sv(lys) (Cu exposure) and Nv(LYS) (Cd and Zn exposures) returned to control values after depuration. It has been therefore demonstrated that the biomarkers used are reversible and return towards control levels once metal exposure ceases. Overall, it is concluded that Vv(BSD), MT-levels and lysosomal responses are valuable biomarkers to assess metal exposure and its effects in turbot, although in quantitative terms the biomarker response varied between metals.

Tissue-specific cadmium and metallothionein levels in rainbow trout chronically acclimated to waterborne or dietary cadmium

Rainbow trout were exposed to a sublethal concentration of waterborne Cd (0 or 3 microg/L) or dietary Cd (0 or 500 mg/kg dry wt) for 30 days to induce acclimation, and tissue Cd and metallothionein (MT) levels were examined. The greatest Cd concentrations were observed in the kidney followed by the gills and liver of the fish exposed to Cd via water, but in the gut tissues followed by the kidney, liver, and gills for dietary-exposed fish, reflecting a variation depending on the route of Cd exposure. Some MT was found in the nonacclimated naïve fish with no experience of elevated Cd exposure, and these background MT levels were quite high in the posterior intestine (480 microg/g), cecae (257 microg/g), and liver (248 microg/g) relative to other tissues (7-50 microg/g). With exposure to both waterborne and dietary Cd, MT levels rose significantly in all observed tissues. The increases relative to the control levels of MT in naïve fish were in the order: kidney (5.4 times) > gills (4.6) > liver (1.3) for the waterborne exposure group, and in the order kidney (19.3 times) >> cecae and posterior intestine (approximately 6.5 times) > liver and stomach (approximately 5 times) > midintestine (4.3 times) > gills (2.1 times) for the dietary exposure group. At 24 hours after an acute gastrointestinal dose of Cd (276 microg/kg) infused into the stomach of dietary exposure groups, large increases of total Cd but not MT levels were found in the gut tissues of nonacclimated fish; in the Cd-acclimated fish, the posterior intestine was greatly affected with decreases in Cd (71%), Zn (33%), Cu (70%) and MT (46%) levels, suggesting an enhanced sloughing of tissue materials after infusion. Exposure to Cd did not cause any notable decrease of Zn or Cu in any tissue, except that found in the posterior intestine. However, a molar analysis indicated that although Cd levels remained less than MT binding capacity in both waterborne and dietary exposure groups, the total metal levels (Cd + Zn + Cu) greatly exceeded MT binding capacity in all tissues of Cd-exposed fish, suggesting a potential competition of Cd with other metals for binding sites on MT and non-MT proteins in the tissues.

The Multifunctional Fish Gill: Dominant Site of Gas Exchange, Osmoregulation, Acid-Base Regulation, and Excretion of Nitrogenous Waste

The fish gill is a multipurpose organ that, in addition to providing for aquatic gas exchange, plays dominant roles in osmotic and ionic regulation, acid-base regulation, and excretion of nitrogenous wastes. Thus, despite the fact that all fish groups have functional kidneys, the gill epithelium is the site of many processes that are mediated by renal epithelia in terrestrial vertebrates. Indeed, many of the pathways that mediate these processes in mammalian renal epithelial are expressed in the gill, and many of the extrinsic and intrinsic modulators of these processes are also found in fish endocrine tissues and the gill itself. The basic patterns of gill physiology were outlined over a half century ago, but modern immunological and molecular techniques are bringing new insights into this complicated system. Nevertheless, substantial questions about the evolution of these mechanisms and control remain.

Ultrastructural changes in various organs of the fish Puntius gonionotus fed cadmium-enriched cyanobacteria

The accumulation and toxicity of cadmium in Puntius gonionotus fish that consumed the cyanobacterium Spirulina platensis contaminated with cadmium were studied. Fish were fed cadmium-contaminated cells for 4 weeks, after which cadmium accumulation in various organs was determined. The highest cadmium content was found in the kidney (56.0 microg Cd/g wet weight). Cadmium was not detected in the gill during the entire 4 weeks of cadmium feeding. Histopathological alteration of cells was observed in the gill, kidney, and liver. The results showed that dietary cadmium caused hypertrophy and edema of gill filaments. Coagulative necrosis and karyolysis of the nucleus were observed in the kidney. Vacuoles and hyaline droplets had accumulated in the epithelial cells of the proximal tubule. In the liver vacuolation of the cytoplasm, infiltration of macrophages, and focal necrosis were found. The ultrastructural changes that occurred in the cells of different organs were similar. These included a proliferation of vacuoles and lysosomes, formation of myelin bodies, degranulation, vesiculation, and dilation of rough endoplasmic reticulum, as well as swelling of mitochondria with loss of cristae.

Physiological effects of dietary cadmium acclimation and waterborne cadmium challenge in rainbow trout: respiratory, ionoregulatory, and stress parameters

A suite of respiratory, acid-base, ionoregulatory, hematological, and stress parameters were examined in adult rainbow trout (Oncorhynchus mykiss) after chronic exposure to a sublethal level of dietary Cd (500 mg/kg diet) for 45 days and during a subsequent challenge to waterborne Cd (10 microg/L) for 72 h. Blood sampling via an indwelling arterial catheter revealed that dietary Cd had no major effects on blood gases, acid-base balance, and plasma ions (Ca(2+), Mg(2+), K(+), Na(+), and Cl(-)) in trout. The most notable effects were an increase in hematocrit (49%) and hemoglobin (74%), and a decrease in the plasma total ammonia (43%) and glucose (49%) of the dietary Cd-exposed fish relative to the nonexposed controls. Dietary Cd resulted in a 26-fold increase of plasma Cd level over 45 days (approximately 24 ng/mL). The fish exposed to dietary Cd showed acclimation with increased protection against the effects of waterborne Cd on arterial blood P(aCO2) and pH, plasma ions, and stress indices. After waterborne Cd challenge, nonacclimated fish, but not Cd-acclimated fish, exhibited respiratory acidosis. Plasma Ca(2+) levels declined from the prechallenge level, but the effect was more pronounced in nonacclimated fish (44%) than in Cd-acclimated fish (14%) by 72 h. Plasma K(+) was elevated only in the nonacclimated fish. Similarly, waterborne Cd caused an elevation of all four traditional stress parameters (plasma total ammonia, cortisol, glucose, and lactate) only in the nonacclimated fish. Thus, chronic exposure to dietary Cd protects rainbow trout against physiological stress caused by waterborne Cd and both dietary and waterborne Cd should be considered in determining the extent of Cd toxicity to fish.

Genotoxic effects of cadmium chloride and azadirachtin treated singly and in combination in fish

The genotoxic effects of cadmium chloride (CdCl(2)) and azadirachtin (Aza) were assessed singly and conjointly in a fish, Oreochromis mossambicus, with endpoints such as chromosome aberrations, abnormal red cell nuclei, abnormal sperm morphology, and protein content (both qualitative and quantitative) of selected tissues, namely, muscle, heart, eye, brain, gill, liver, spleen, and kidney. The primary objectives were, first, to examine if CdCl(2), a common pollutant, and Aza, a natural product of the neem plant used extensively as an 'ecofriendly' agent for many purposes, had any genotoxic effect of their own on nontarget aquatic organisms of economic importance; and second, if Aza could have any ameliorating effect on CdCl(2)-induced genotoxicity in O. mossambicus tissues. As compared with distilled water-treated controls, both CdCl(2) and Aza induced genotoxicity in O. mossambicus, the former in greater quantity than that produced by Aza. However, Cd-induced toxicity in O. mossambicus appeared to be ameliorated to some extent by Aza.

Ameliorating effect of beta-carotene on ethylmethane sulphonate-induced genotoxicity in the fish Oreochromis mossambicus

Genotoxic effects have been assessed in the fish Oreochromis mossambicus treated separately and conjointly with 0.2% ethylmethane sulphonate (EMS) and 0.05% beta-carotene (BC) during five different time periods (6, 24, 48, 72 and 96 h) by analysis of endpoints such as chromosome aberrations, abnormal red blood cell nuclei, abnormal sperm morphology and protein contents (both qualitative and quantitative) of selected tissues, viz. muscle, heart, eye, brain, gill, liver, spleen and kidney. In addition, the relative efficacy of three doses of BC 0.02, 0.05 and 0.1%, in ameliorating genotoxic effects of 0.2% EMS was also tested after a treatment period of 48 h. EMS caused chromosomal aberrations, nuclear anomalies in red blood cells, abnormal sperm morphology and an apparent alteration of protein synthesis in various tissues. Some of these genotoxic effects of EMS appeared to be ameliorated by all three doses of BC, of which the 0.02% dose showed a marginally better efficacy.

Gill circulation: regulation of perfusion distribution and metabolism of regulatory molecules

The fish gill is the primary regulatory interface between internal and external milieu and a variety of neurocrine, endocrine, paracrine, and autocrine signals coordinate and control gill functions. Many of these messengers also affect gill vascular resistance, and they, in turn, may be inactivated (or activated) by branchial vessels. Few studies have critically addressed how flow is distributed within the gill filament, the physiological consequences thereof, or the impact of gill hormone metabolism on gill and systemic homeostasis. In most fish, the entire cardiac output perfuses the arterioarterial pathway, and this network probably accounts for the majority of passive- and stimulus-induced changes in vascular resistance. The in-series arrangement of the extensive gill microcirculation with systemic vessels is also indicative of a high capacity for metabolism of plasma-borne messengers as well as xenobiotics. Adenosine, arginine vasotocin (AVT), and endothelin (ET) are the most potent gill constrictors identified to date, and all decrease lamellar perfusion. Perhaps not surprising, they are also inactivated by gill vessels. Acetylcholine favors perfusion of the alamellar filamental vasculature, although the physiological relevance of acetylcholine-mediated responses remains unclear. Angiotensin, bradykinin, urotensin, natriuretic peptides, prostaglandins, and nitric oxide are vasoactive to varying degrees, but their effects on intrafilamental blood flow are unknown. If form befits function, then the complex vascular anatomy of the gill suggests a level of regulatory sophistication unparalleled in other vertebrate organs. Resolution of these issues will be technically challenging but unquestionably rewarding.