Adaptations to in situ feeding: novel nutrient acquisition pathways in an ancient vertebrate

During feeding, hagfish may immerse themselves in the body cavities of decaying carcasses, encountering high levels of dissolved organic nutrients. We hypothesized that this feeding environment might promote nutrient acquisition by the branchial and epidermal epithelia. The potential for Pacific hagfish, Eptatretus stoutii, to absorb amino acids from the environment across the skin and gill was thus investigated. l-alanine and glycine were absorbed via specific transport pathways across both gill and skin surfaces, the first such documentation of direct organic nutrient acquisition in a vertebrate animal. Uptake occurred via distinct mechanisms with respect to concentration dependence, sodium dependence and effects of putative transport inhibitors across each epithelium. Significant differences in the absorbed amino acid distribution between the skin of juveniles and adults were noted. The ability to absorb dissolved organic matter across the skin and gill may be an adaptation to a scavenging lifestyle, allowing hagfish to maximize sporadic opportunities for organic nutrient acquisition. From an evolutionary perspective, hagfish represent a transitory state between the generalized nutrient absorption pathways of aquatic invertebrates and the more specialized digestive systems of aquatic vertebrates.

In vitro characterization of cadmium transport along the gastro-intestinal tract of freshwater rainbow trout (Oncorhynchus mykiss)

An in vitro gut sac technique was used to examine the mechanism(s) of cadmium (Cd) uptake along the gastro-intestinal tract (GIT) of rainbow trout (Oncorhynchus mykiss). The spatial distribution of Cd between three compartments (mucus-binding, mucosal epithelium, and transport into blood space) was determined using a modified Cortland saline containing 50μM Cd (as CdCl(2)) labeled with (109)Cd radiotracer. Taking into account total surface areas, the order of relative importance for total Cd uptake rate was: posterior intestine>anterior intestine>stomach>mid intestine. Cd transport was not inhibited by experimentally reducing fluid transport rates by manipulation of osmotic gradients using mannitol, but was sensitive to internal luminal pressure changes, suggesting a mechanosensitive pathway. Q(10) values (1, 11, and 19°C) indicated a facilitated transport of Cd in the anterior- and mid-intestine. The effects of 10mM Ca on the kinetics of Cd uptake suggest the presence of a common uptake pathway for Cd and Ca in the stomach, anterior-, and mid-intestine. Further evidence of a shared route of entry was found using three Ca channel blockers, lanthanum, verapamil, and nifedipine: both voltage-insensitive and voltage-sensitive Ca channels appear to be present in either some, or all portions of the GIT. Elevated Fe (500μM), Mg (50mM), and Zn (500μM) showed varying degrees of inhibition of Cd transport depending on the compartment and segment of the GIT. Overall it appears that there are multiple sites, and mechanisms, of Cd uptake along the GIT of rainbow trout.

Acute toxicity, accumulation and tissue distribution of copper in the blue crab Callinectes sapidus acclimated to different salinities: in vivo and in vitro studies

In vivo and in vitro studies were performed to evaluate acute toxicity, organ-specific distribution, and tissue accumulation of copper in Callinectes sapidus acclimated to two different experimental salinities (2 and 30 ppt). Blue crabs were quite tolerant to copper. Acute dissolved copper toxicity (96-h LC(50) and its corresponding 95% confident interval) was higher at salinity 2 ppt (5.3 (3.50-8.05) μM Cu) than at 30 ppt (53.0 (27.39-102.52) μM Cu). The difference between salinities can be completely explained based on the water chemistry because it disappeared when 96-h LC(50) values were expressed as the free Cu(2+) ion (3.1 (1.93-4.95) μM free Cu at 2 ppt versus 5.6 (2.33-13.37) μM free Cu at 30 ppt) or the Cu(2+) activity (1.4 (0.88-2.26) μM Cu activity at 2 ppt versus 1.7 (0.71-4.07) μM Cu activity at 30 ppt). The relationships between gill Cu burden and % mortality were very similar at 2 and 30 ppt, in accord with the Biotic Ligand Model. In vivo experiments showed that copper concentration in the hemolymph is not dependent on metal concentration in the surrounding medium at either experimental salinity. They also showed that copper flux into the gills is higher than into other tissues analyzed, and that anterior and posterior gills are similarly important sites of copper accumulation at both experimental salinities. In vitro experiments with isolated-perfused gills showed that there is a positive relationship between copper accumulation in this tissue and the metal concentration in the incubation media for both anterior and posterior gills. A similar result was observed at both low and high salinities. Furthermore, in vitro experiments showed that copper accumulation in posterior gills is also positively and strongly dependent on the incubation time with copper. Gill copper accumulation occurred at a lower rate in the first 2h of metal exposure, increasing markedly after this "steady-state" period. This finding was corroborated by a significant increase in copper influx to the gill perfusate (corresponding to crab hemolymph) after this time, measured using (64)Cu. In vivo, after uptake from solution, (64)Cu was primarily accumulated in the gills and the rest of the body rather than in the hemolymph, hepatopancreas, or other internal tissues. Overall, the present findings indicate that gills are a key target organ for copper accumulation, as well as an important biological barrier against the excessive uptake of copper into the hemolymph and the subsequent distribution of this metal to internal organs of the blue crab.

Utility of tissue residues for predicting effects of metals on aquatic organisms

As part of a SETAC Pellston Workshop, we evaluated the potential use of metal tissue residues for predicting effects in aquatic organisms. This evaluation included consideration of different conceptual models and then development of several case studies on how tissue residues might be applied for metals, assessing the strengths and weaknesses of these different approaches. We further developed a new conceptual model in which metal tissue concentrations from metal-accumulating organisms (principally invertebrates) that are relatively insensitive to metal toxicity could be used as predictors of effects in metal-sensitive taxa that typically do not accumulate metals to a significant degree. Overall, we conclude that the use of tissue residue assessment for metals other than organometals has not led to the development of a generalized approach as in the case of organic substances. Species-specific and site-specific approaches have been developed for one or more metals (e.g., Ni). The use of gill tissue residues within the biotic ligand model is another successful application. Aquatic organisms contain a diverse array of homeostatic mechanisms that are both metal- and species-specific. As a result, use of whole-body measurements (and often specific organs) for metals does not lead to a defensible position regarding risk to the organism. Rather, we suggest that in the short term, with sufficient validation, species- and site-specific approaches for metals can be developed. In the longer term it may be possible to use metal-accumulating species to predict toxicity to metal-sensitive species with appropriate field validation.

Niche dimensions in fishes: an integrative view

Current shifts in ecosystem composition and function emphasize the need for an understanding of the links between environmental factors and organism fitness and tolerance. The examples discussed here illustrate how recent progress in the field of comparative physiology may provide a better mechanistic understanding of the ecological concepts of the fundamental and realized niches and thus provide insights into the impacts of anthropogenic disturbance. Here we argue that, as a link between physiological and ecological indicators of organismal performance, the mechanisms shaping aerobic scope and passive tolerance set the dimensions of an animal's niche, here defined as its capacity to survive, grow, behave, and interact with other species. We demonstrate how comparative studies of cod or killifish populations in a latitudinal cline have unraveled mitochondrial mechanisms involved in establishing a species' niche, performance, and energy budget. Riverine fish exemplify how the performance windows of various developmental stages follow the dynamic regimes of both seasonal temperatures and river hydrodynamics, as synergistic challenges. Finally, studies of species in extreme environments, such as the tilapia of Lake Magadi, illustrate how on evolutionary timescales functional and morphological shifts can occur, associated with new specializations. We conclude that research on the processes and time course of adaptations suitable to overcome current niche limits is urgently needed to assess the resilience of species and ecosystems to human impact, including the challenges of global climate change.

Phylogeography and conservation genetics of Lake Qinghai scaleless carp Gymnocypris przewalskii

The objective of this study was to examine the spatial genetic relationships of the Lake Qinghai scaleless carp Gymnocypris przewalskii within the Lake Qinghai system, determining whether genetic evidence supports the current taxonomy of Gymnocypris przewalskii przewalskii and Gymnocypris przewalskii ganzihonensis and whether Gymnocypris przewalskii przewalskii are returning to their natal rivers to spawn. Comparison of mitochondrial (control region) variation (42 haplotypes in 203 fish) of G. przewalskii with the postulated ancestral species found in the Yellow River, Gymnocypris eckloni (10 haplotypes in 23 fish), indicated no haplotype sharing, but incomplete lineage sorting. Consistent with the sub-species status, an AMOVA indicated that the Ganzi River population was significantly different from all other river populations (F(ST) = 0·1671, P < 0·001). No genetic structure was found among the other rivers in the Lake Qinghai catchment. An AMOVA of amplified fragment length polymorphism (AFLP) loci, however, revealed significant genetic differences between most spawning populations (F(ST) = 0·0721, P < 0·001). Both mitochondrial and AFLP data found significant differences among G. p. przewalskii, G. p. ganzihonensis and G. eckloni (F(ST) values of 0·1959 and 0·1431, respectively, P < 0·001). Consistent with the incomplete lineage sorting, Structure analysis of AFLP loci showed evidence of five clusters. One cluster is shared among all sample locations, one is unique to G. p. ganzihonensis and G. eckloni, and the others are mostly found in G. p. przewalskii. Genetic evidence therefore supports the current taxonomy, including the sub-species status of G. p. ganzihonensis, and is consistent with natal homing of most Lake Qinghai populations. These findings have significant implications for the conservation and management of this unique and threatened species. The evidence suggests that G. p. przewalskii should be treated as a single population for conservation purposes. Exchangeability of the populations, however, should not be used to promote homogenization of fish spawning in the different rivers. As some degree of genetic divergence was detected in this study, it is recommended that the spawning groups be treated as separate management units.

Acid-base responses to feeding and intestinal Cl- uptake in freshwater- and seawater-acclimated killifish, Fundulus heteroclitus, an agastric euryhaline teleost

Marine teleosts generally secrete basic equivalents (HCO(3)(-)) and take up Na(+) and Cl(-) in the intestine so as to promote absorption of H(2)O. However, neither the integration of these functions with feeding nor the potential role of the gut in ionoregulation and acid-base balance in freshwater have been well studied. The euryhaline killifish (Fundulus heteroclitus) is unusual in lacking both an acid-secreting stomach and a mechanism for Cl(-) uptake at the gills in freshwater. Responses to a satiation meal were evaluated in both freshwater- and seawater-acclimated killifish. In intact animals, there was no change in acid or base flux to the external water after the meal, in accord with the absence of any post-prandial alkaline tide in the blood. Indeed, freshwater animals exhibited a post-prandial metabolic acidosis ('acidic tide'), whereas seawater animals showed no change in blood acid-base status. In vitro gut sac experiments revealed a substantially higher rate of Cl(-) absorption by the intestine in freshwater killifish, which was greatest at 1-3 h after feeding. The Cl(-) concentration of the absorbate was higher in preparations from freshwater animals than from seawater killifish and increased with fasting. Surprisingly, net basic equivalent secretion rates were also much higher in preparations from freshwater animals, in accord with the 'acidic tide'; in seawater preparations, they were lowest after feeding and increased with fasting. Bafilomycin (1 micromol l(-1)) promoted an 80% increase in net base secretion rates, as well as in Cl(-) and fluid absorption, at 1-3 h post-feeding in seawater preparations only, explaining the difference between freshwater and seawater fish. Preparations from seawater animals at 1-3 h post-feeding also acidified the mucosal saline, and this effect was associated with a marked rise in P(CO(2)), which was attenuated by bafilomycin. Measurements of chyme pH from intact animals confirmed that intestinal fluid (chyme) pH and basic equivalent concentration were lowest after feeding in seawater killifish, whereas P(CO(2)) was greatly elevated (80-95 Torr) in chyme from both seawater and freshwater animals but declined to lower levels (13 Torr) after 1-2 weeks fasting. There were no differences in pH, P(CO(2)) or the concentrations of basic equivalents in intestinal fluid from seawater versus freshwater animals at 12-24 h or 1-2 weeks post-feeding. The results are interpreted in terms of the absence of gastric HCl secretion, the limitations of the gills for acid-base balance and Cl(-) transport, and therefore the need for intestinal Cl(-) uptake in freshwater killifish, and the potential for O(2) release from the mucosal blood flow by the high P(CO(2)) in the intestinal fluids. At least in seawater killifish, H(+)-ATPase running in parallel to HCO(3)(-):Cl(-) exchange in the apical membranes of teleost enterocytes might reduce net base secretion and explain the high P(CO(2)) in the chyme after feeding.

Signatures of contamination in invasive round gobies (Neogobius melanostomus): a double strike for ecosystem health?

The invasive round goby has a recognised role in transferring contaminants through foodwebs, but little work has been done on contaminant impacts on round gobies themselves. Here we present the first case study of contaminant biomarkers and subpopulation structure variation in round gobies, in relation to habitat contamination, within a Canadian Area of Concern, Hamilton Harbour. Copper and cadmium were elevated in livers of fish from contaminated habitats. Although catch abundances were similar across sites, fish were smaller, a greater proportion of fish were female and more males were in reproductive condition in contaminated sites. Fish from contaminated areas showed more fin loss. Males from contaminated sites showed intersex gonads and genitalia. Ethoxyresorufin-o-deethylase (EROD) activity was higher in fish collected near polycyclic aromatic hydrocarbon (PAH)-rich sediments. The results indicate that contaminants impact the characteristics of round goby populations, which could affect ecosystems beyond toxicant biomagnification. This study also confirms that round gobies can be abundant in polluted habitats, which may draw predators-facilitating mobilisation of contaminants in foodwebs.

Rh glycoprotein expression is modulated in pufferfish (Takifugu rubripes) during high environmental ammonia exposure

Rhesus (Rh) protein involvement in ammonia transport processes in freshwater fish has received considerable attention; however, parallel investigations in seawater species are scant. We exposed pufferfish to high environmental ammonia (HEA; 1 and 5 mmol l–1 NH4HCO3) and evaluated the patterns of ammonia excretion and gill Rh mRNA and protein expression. Gill H+-ATPase, NHE1, NHE2, NHE3, Na+/K+-ATPase (NKA), Na+/K+/2Cl– co-transporter (NKCC1) mRNA, H+-ATPase activity, NKA protein and activity, were also quantified. Activation of NKA by NH4+ was demonstrated in vitro. The downregulation of Rhbg mRNA and simultaneous upregulations of Rhcg1, H+-ATPase, NHE3, NKA, NKCC1 mRNA, H+-ATPase activity, and NKA protein and activity levels suggested that during HEA, ammonia excretion was mediated mainly by mitochondria-rich cells (MRCs) driven by NKA with basolateral NH4+ entry via NKA and/or NKCC1, and apical NH3 extrusion via Rhcg1. Reprotonation of NH3 by NHE3 and/or H+-ATPase would minimise back flux through the Rh channels. Downregulated Rhbg and Rhag mRNA observed in the gill during HEA suggests a coordinated protective response to minimise the influx of external ammonia via the pavement cells and pillar cells, respectively, while routing ammonia excretion through the MRCs. Exposure to hypercapnia (1% CO2 in air) resulted in downregulated gill and erythrocyte Rhag mRNA. Surprisingly, Rhag, Rhbg, Rhcg1 and Rhcg2 proteins responded to both hypercapnia and HEA with changes in their apparent molecular masses. A dual NH3/CO2 transport function of the pufferfish Rh proteins is therefore suggested. The results support and extend an earlier proposed model of pufferfish gill ammonia excretion that was based on immunolocalisation of the Rh proteins. Passive processes and/or Rhbg and Rhcg2 in the pavement cells may maintain basal levels of plasma ammonia but elevated levels may require active excretion via NKA and Rhcg1 in the MRCs.

Effects of waterborne silver in a marine teleost, the gulf toadfish (Opsanus beta): effects of feeding and chronic exposure on bioaccumulation and physiological responses

Marine teleosts drink seawater, and the digestive tract is a key organ of osmoregulation. The gastro-intestinal tract therefore offers a second site for the potential uptake and toxicity of waterborne metals, but how these processes might interact with the digestive functions of the tract has not been investigated previously. We therefore compared the responses of adult gulf toadfish (Opsanus beta, collected from the wild) to a chronic 22d exposure to waterborne Ag (nominally 200 microg L(-1)=1.85 micromol L(-1)), in the presence or absence of daily satiation feeding (shrimp). Ag exposure did not affect voluntary feeding rate. Feeding reduced the net whole body accumulation of Ag by >50%, with reductions in liver concentrations (high) and white muscle concentrations (relatively low) playing the largest quantitative roles. Feeding also protected against Ag buildup in the esophagus-stomach and kidney, and increased biliary and urinary Ag concentrations. The gill was the only tissue to show the opposite response. Although terminal plasma Na(+), Cl(-), and Mg(2+) concentrations were unaffected, there were complex interactive effects on osmoregulatory functions of the gastro-intestinal tract, including drinking rate, gut fluid volumes, and intestinal base secretion rates. At the end of the exposure, the plasma clearance kinetics of an arterially injected tracer dose of (110 m)Ag were faster in toadfish that had been chronically exposed to waterborne Ag, and (110 m)Ag accumulation in their red blood cells was reduced. After 32 h, higher amounts of (110 m)Ag were found in bile and urine, but lower amounts in the intestine of the Ag-exposed toadfish; there were no other differences in tissue-specific distribution. The results suggest that feeding reduces waterborne Ag uptake through the digestive tract and alters physiological responses, while chronic exposure enhances regulatory functions. The time-dependent actions of the liver in Ag scavenging and detoxification are highlighted.

Can the biotic ligand model predict Cu toxicity across a range of pHs in softwater-acclimated rainbow trout?

This study examined the effects of pH (5.0-8.5) on the toxicity of waterborne Cu to juvenile rainbow trout (Oncorhynchus mykiss) in soft water under flow-through conditions. Relationships between 96 h or 30 day Cu toxicity and 24 h lethal Cu accumulation on the gills (24 h LA(50-Acute) or 24 h LA(50-Chronic)) were examined in the context of predictions made using the biotic ligand model (BLM). Acute toxicity was relatively constant across pHs except for a 2- to 3-fold higher LC(50) at pH 5.0. In the chronic exposure, the fish had similar tolerance to Cu from pH 5.0 to 8.0, but were 3- to 4-fold more tolerant at pH 8.5. This pattern was not captured by the current BLM which predicts that acute and chronic LC(50) values should increase progressively from pH 5.0 to 8.5, with much greater values than those observed at the higher pH range. BLM-based water quality criteria would not be protective for trout at pH 8.0 or 8.5 in acute exposure to Cu in soft water. The measured 24 h LA(50-Acute) and LA(50-chronic) at pH 8.5 were higher, and 24 h LA(50-Chronic) at pH 5.0 was lower than those at the other pHs. This study indicates that gill Cu bioaccumulation does not explain toxicity at high or low pH, and the BLM needs revision to adequately predict Cu toxicity to trout in soft water.

Cortisol reduces paracellular permeability and increases occludin abundance in cultured trout gill epithelia

A role for the tight junction (TJ) protein occludin in the regulation of gill paracellular permeability was investigated using primary cultured "reconstructed" freshwater (FW) rainbow trout gill epithelia composed solely of pavement cells. Cortisol treatment reduced epithelial permeability characteristics, measured as changes in transepithelial resistance (TER) and paracellular [3H]PEG-4000 flux. Cortisol also reduced net Na+ flux rates when epithelia were exposed to apical FW. cDNA encoding for the TJ protein occludin was cloned from rainbow trout and found to be particularly abundant in gill tissue. In cultured gill preparations, occludin immunolocalized to the TJ complex and transcript abundance dose-dependently increased in response to cortisol treatment in association with reduced paracellular permeability. Occludin protein abundance also increased in response to cortisol treatment. However, occludin mRNA levels did not change in response to apical FW exposure, and [3H]PEG-4000 permeability did not decrease. These data support a role for occludin in the endocrine regulation of paracellular permeability across gill epithelia of fishes.

Functional characterization of Rhesus glycoproteins from an ammoniotelic teleost, the rainbow trout, using oocyte expression and SIET analysis

Recent experimental evidence from rainbow trout suggests that gill ammonia transport may be mediated in part via Rhesus (Rh) glycoproteins. In this study we analyzed the transport properties of trout Rh proteins (Rhag, Rhbg1, Rhbg2, Rhcg1, Rhcg2, Rh30-like) expressed in Xenopus oocytes, using the radiolabeled ammonia analogue [14C]methylamine, and the scanning ion electrode technique (SIET). All of the trout Rh proteins, except Rh30-like, facilitated methylamine uptake. Uptake was saturable, with Km values ranging from 4.6 to 8.9 mmol l−1. Raising external pH from 7.5 to 8.5 resulted in 3- to 4-fold elevations in Jmax values for methylamine; Km values were unchanged when expressed as total or protonated methylamine. Efflux of methylamine was also facilitated in Rh-expressing oocytes. Efflux and influx rates were stimulated by a pH gradient, with higher rates observed with steeper H+ gradients. NH4Cl inhibited methylamine uptake in oocytes expressing Rhbg1 or Rhcg2. When external pH was elevated from 7.5 to 8.5, the Ki for ammonia against methylamine transport was 35–40% lower when expressed as total ammonia or NH4+, but 5- to 6-fold higher when expressed as NH3. With SIET we confirmed that ammonia uptake was facilitated by Rhag and Rhcg2, but not Rh30-like proteins. Ammonia uptake was saturable, with a comparable Jmax but lower Km value than for total or protonated methylamine. At low substrate concentrations, the ammonia uptake rate was greater than that of methylamine. The Km for total ammonia (560 μmol l−1) lies within the physiological range for trout. The results are consistent with a model whereby NH4+ initially binds, but NH3 passes through the Rh channels. We propose that Rh glycoproteins in the trout gill are low affinity, high capacity ammonia transporters that exploit the favorable pH gradient formed by the acidified gill boundary layer in order to facilitate rapid ammonia efflux when plasma ammonia concentrations are elevated.

Water chemistry alters gene expression and physiological end points of chronic waterborne copper exposure in zebrafish, Danio rerio

This is the first study to implement a genomic approach to ascertain both transcriptional and functional end points of chronic Cu toxicity in fish associated with experimentally manipulated water chemistries. Over 21 d, zebrafish acclimated to softwater (Na(+) = 0.06 mM, Ca(2+) = 0.08 mM, Mg(2+) = 0.03 mM) were exposed to the following: soft-water (Ctrl); 12 microg L(-1) Cu (Cu); 3.3 mM Na(+) (Na); 3.3 mM Na(+) + 12 microg L(-1) Cu (Na + Cu); 3.3 mM Ca(2+) (Ca); or 3.3 mM Ca(2+) + 12 microg L(-1) Cu (Ca + Cu). Although effective at reducing Cu load in all tissues, Na(+) in the presence of Cu did not decrease the degree of oxidative damage, particularly in the gill and gut. In contrast, Ca + Cu treatment decreased Cu accumulation in gill, but not liver or gut, with no reduction in oxidative damage. Transcriptional analysis of candidate genes (atp7a, ctr1, ECaC, esr1) showed principally a down regulation of transcripts with the Cu only treatment, while Ca + Cu treatment restored some of the genes to control levels. Conversely, the Na + Cu treatment had a strong, opposing affect when compared to that of Cu alone. Zebrafish Affymetrix GeneChips revealed significantly clustered patterns of expression. Changes in expression induced by Cu appeared to be opposite to the majority of the other treatments. Our data on the preventative or enhancing effects of Na(+) and Ca(2+) both alone and in the presence of Cu, may, in the future, facilitate the incorporation of gene expression end points into a biotic ligand model predicting chronic Cu toxicity in this tropical model species of genomic importance.

Rhesus glycoprotein and urea transporter genes in rainbow trout embryos are upregulated in response to alkaline water (pH 9.7) but not elevated water ammonia

Recent studies have shown that genes for the putative ammonia transporter, Rhesus glycoproteins (Rh) and the facilitated urea transporter (UT) are expressed before hatching in rainbow trout (Oncorhychus mykiss Walbaum) embryos. We tested the hypothesis that Rh and UT gene expressions are regulated in response to environmental conditions that inhibit ammonia excretion during early life stages. Eyed-up embryos (22 days post-fertilization (dpf)) were exposed to control (pH 8.3), high ammonia (1.70 mmol l(-1) NH4HCO3) and high pH (pH 9.7) conditions for 48h. With exposure to high water ammonia, ammonia excretion rates were reversed, tissue ammonia concentration was elevated by 9-fold, but there were no significant changes in mRNA expression relative to control embryos. In contrast, exposure to high water pH had a smaller impact on ammonia excretion rates and tissue ammonia concentrations, whereas mRNA levels for the Rhesus glycoprotein Rhcg2 and urea transporter (UT) were elevated by 3.5- and 5.6-fold, respectively. As well, mRNAs of the genes for H+ATPase and Na+/H+ exchanger (NHE2), associated with NH3 excretion, were also upregulated by 7.2- and 13-fold, respectively, in embryos exposed to alkaline water relative to controls. These results indicate that the Rhcg2, UT and associated transport genes are regulated in rainbow trout embryos, but in contrast to adults, there is no effect of high external ammonia at this stage of development.

Copper binding dynamics and olfactory impairment in fathead minnows (Pimephales promelas)

When fish are exposed to sublethal, environmentally relevant Cu concentrations, olfactory acuity is impaired. The goals of the present study were to investigate the binding dynamics of waterborne Cu in the olfactory epithelium (OE), to examine the influence of calcium (Ca(2+)) on Cu binding, and to link Cu-OE binding to changes in olfactory acuity. Using short-term in vivo waterborne exposures to (64)Cu, we found that Cu accumulates rapidly in the OE, reaching a plateau by 3 h. The binding affinity (log K(Cu-OE)) and binding capacity (B(max)) of (64)Cu in the OE were 6.7 and 10.0 nmol Cu g(-1), respectively. As waterborne Ca(2+) was increased from 50 to 1000 microM L(-1), the B(max) of Cu decreased by approximately 50% while the log K(Cu-OE) remained constant, indicative of noncompetitive inhibition. Using electro-olfactograms (EOG), short-term exposures to 160 and 240 nmol Cu L(-1) were found to reduce olfactory responses to 10(-5) M l-arginine by 72 and 79%, respectively. Short-term exposure to 160 nmol Cu L(-1) also caused a 15-fold reduction in behavioral responses to a food stimulus. Interestingly, increasing waterborne Ca(2+) did not reduce the effects of Cu on EOG or behavioral responses. These results demonstrate that short-term, environmentally realistic concentrations of Cu not only bind to the OE of fathead minnows but also impair their olfactory sensitivity and behavioral responses to olfactory stimuli. Waterborne Ca(2+) reduces Cu-OE binding but does not protect against olfactory impairment.

Case study--leprosy

We present the case of a 26 year old Indian base worker who attended the Role 2 enhanced hospital in Iraq with a case of leprosy. The patient presented four times over a 12 month period with non-specific pain in the right hand and forearm combined with a large lesion of dry skin and reduced sensation in the forearm. A clinical diagnosis of leprosy was made, which was subsequently confirmed as paucibacillary leprosy by skin smears sent to the UK. It was not possible to treat the patient locally and a recommendation made to the patient's employer that the patient return to India to commence treatment.

Post-prandial metabolic alkalosis in the seawater-acclimated trout: the alkaline tide comes in

The consequences of feeding and digestion on acid-base balance and regulation in a marine teleost (seawater-acclimated steelhead trout; Oncorhynchus mykiss) were investigated by tracking changes in blood pH and [HCO3-], as well as alterations in net acid or base excretion to the water following feeding. Additionally the role of the intestine in the regulation of acid-base balance during feeding was investigated with an in vitro gut sac technique. Feeding did not affect plasma glucose or urea concentrations, however, total plasma ammonia rose during feeding, peaking between 3 and 24 h following the ingestion of a meal, three-fold above resting control values (approximately 300 micromol ml(-1)). This increase in plasma ammonia was accompanied by an increase in net ammonia flux to the water (approximately twofold higher in fed fish versus unfed fish). The arterial blood also became alkaline with increases in pH and plasma [HCO3-] between 3 and 12 h following feeding, representing the first measurement of an alkaline tide in a marine teleost. There was no evidence of respiratory compensation for the measured metabolic alkalosis, as Pa CO2 remained unchanged throughout the post-feeding period. However, in contrast to an earlier study on freshwater-acclimated trout, fed fish did not exhibit a compensating increase in net base excretion, but rather took in additional base from the external seawater, amounting to approximately 8490 micromol kg(-1) over 48 h. In vitro experiments suggest that at least a portion of the alkaline tide was eliminated through increased HCO3- secretion coupled to Cl- absorption in the intestinal tract. This did not occur in the intestine of freshwater-acclimated trout. The marked effects of the external salinity (seawater versus freshwater) on different post-feeding patterns of acid-base balance are discussed.

Gene expression endpoints following chronic waterborne copper exposure in a genomic model organism, the zebrafish, Danio rerio

Although copper (Cu) is an essential micronutrient for all organisms, in excess, waterborne Cu poses a significant threat to fish from the cellular to population level. We examined the physiological and gene expression endpoints that chronic waterborne Cu exposure (21 d) imposes on soft-water acclimated zebrafish at two environmentally relevant concentrations: 8 microg/l (moderate) and 15 microg/l (high). Using a 16,730 65-mer oligonucleotide customized zebrafish microarray chip related to metal metabolism and toxicity to assess the transcriptomic response, we found that 573 genes in the liver responded significantly to Cu exposure. These clustered into three distinct patterns of expression. There was distinct upregulation of a majority of these genes under moderate Cu exposure and a significant downregulation under high Cu exposure. Microarray results were validated by qPCR of eight genes; two genes, metallothionein 2 (mt2) and Na(+)-K(+)-ATPase 1a1 (atp1a1), displayed increased expression under both Cu exposures, indicative of potential genetic endpoints of Cu toxicity, whereas the remaining six genes demonstrated opposing effects at each Cu exposure. Na(+)-K(+)-ATPase enzyme activity decreased during Cu exposure, which may be linked to Cu's competitive effects with Na(+). Whole body cortisol levels were significantly increased in Cu-exposed fish, which prompted an analysis of the promoter region of all significantly regulated genes for glucocorticoid (GRE) and metal (MRE) response elements to dissociate metal- and stress-specific gene responses. Of the genes significantly regulated, 30% contained only a GRE sequence, whereas 2.5% contained only a consensus MRE. We conclude that the indirect effects of Cu exposure regulate gene expression to a much greater degree than the direct effects.

Ionoregulatory physiology of two species of African lungfishes Protopterus dolloi and Protopterus annectens

Basic ionoregulatory physiology was characterized in two species of African lungfish, slender African lungfish Protopterus dolloi and West African lungfish Protopterus annectens, largely under aquatic conditions. There were no substantive differences between the two species. Plasma [Na], [Cl] and [Ca] were only 60-80% of those typical of freshwater teleosts, and plasma Ca activity was particularly low. Unidirectional Na and Cl influx rates from water were also very low, only c. 10% of teleost values, whereas unidirectional Ca influx rates were comparable with teleost rates. Protopterus spp. were fed a 3% ration of bloodworms every 48 h. The bloodworm diet provided similar amounts of Na and Ca as uptake from water, but almost no Cl. Efflux rates of Na and Cl through the urine were greater than via the faeces, whereas the opposite was true for Ca. Net ion flux measurements and ionic balance sheet calculations indicated that (1) both water and dietary uptake routes are important for Na and Ca acquisition; (2) the waterborne route predominates for Cl uptake; (3) unidirectional ion effluxes across the body surface (gills and skin) rather than urine and faeces are the major routes of loss for Na, Cl and Ca. Tissues (muscle, liver, lung, kidney, intestine and heart) and plasma ions were also examined in P. dolloi'terrestrialized' in air for up to 5 months, during which plasma ion concentrations (Na, Cl, Ca and Mg) did not change and there were only a few alterations in tissue ions, that is, increased [Na] in intestine, decreased [Cl] in kidney and increased [Ca] in liver and kidney.

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.

A new paradigm for ammonia excretion in aquatic animals: role of Rhesus(Rh) glycoproteins

Ammonia excretion at the gills of fish has been studied for 80 years, but the mechanism(s) involved remain controversial. The relatively recent discovery of the ammonia-transporting function of the Rhesus (Rh) proteins, a family related to the Mep/Amt family of methyl ammonia and ammonia transporters in bacteria, yeast and plants, and the occurrence of these genes and glycosylated proteins in fish gills has opened a new paradigm. We provide background on the evolution and function of the Rh proteins, and review recent studies employing molecular physiology which demonstrate their important contribution to branchial ammonia efflux. Rhag occurs in red blood cells,whereas several isoforms of both Rhbg and Rhcg occur in many tissues. In the branchial epithelium, Rhcg appears to be localized in apical membranes and Rhbg in basolateral membranes. Their gene expression is upregulated during exposure to high environmental ammonia or internal ammonia infusion, and may be sensitive to synergistic stimulation by ammonia and cortisol. Rhcg in particular appears to be coupled to H+ excretion and Na+uptake mechanisms. We propose a new model for ammonia excretion in freshwater fish and its variable linkage to Na+ uptake and acid excretion. In this model, Rhag facilitates NH3 flux out of the erythrocyte, Rhbg moves it across the basolateral membrane of the branchial ionocyte, and an apical “Na+/NH +4 exchange complex” consisting of several membrane transporters (Rhcg, V-type H+-ATPase, Na+/H+ exchanger NHE-2 and/or NHE-3, Na+ channel) working together as a metabolon provides an acid trapping mechanism for apical excretion. Intracellular carbonic anhydrase(CA-2) and basolateral Na+/HCO –3cotransporter (NBC-1) and Na+/K+-ATPase play indirect roles. These mechanisms are normally superimposed on a substantial outward movement of NH3 by simple diffusion, which is probably dependent on acid trapping in boundary layer water by H+ ions created by the catalysed or non-catalysed hydration of expired metabolic CO2. Profitable areas for future investigation of Rh proteins in fish are highlighted: their involvement in the mechanism of ammonia excretion across the gills in seawater fish, their possible importance in ammonia excretion across the skin, their potential dual role as CO2 transporters,their responses to feeding, and their roles in early life stages prior to the full development of gills.

Characterization of dietary Ni uptake in the rainbow trout, Oncorhynchus mykiss

We characterized dietary Ni uptake in the gastrointestinal tract of rainbow trout using both in vivo and in vitro techniques. Adult trout were fed a meal (3% of body mass) of uncontaminated commercial trout chow, labeled with an inert marker (ballotini beads). In vivo dietary Ni concentrations in the supernatant (fluid phase) of the gut contents averaged from 2 micromoll(-1) to 24 micromoll(-1), and net overall absorption efficiency of dietary Ni was approximately 50% from the single meal, similar to that for the essential metal Cu, adding to the growing evidence of Ni essentiality. The stomach and mid-intestine emerged as important sites of Ni uptake in vivo, accounting for 78.5% and 18.9% of net absorption respectively, while the anterior intestine was a site of net secretion. Most of the stomach uptake occurred in the first 4h. In vitro gut sac studies using radiolabeled Ni (at 30 micromoll(-1)) demonstrated that unidirectional uptake occurred in all segments, with area-weighted rates being highest in the anterior intestine. Differences between in vivo and in vitro results likely reflect the favourable uptake conditions in the stomach, and biliary secretion of Ni in the anterior intestine in vivo. The concentration-dependent kinetics of unidirectional Ni uptake in vitro were biphasic in nature, with a saturable Michaelis-Menten relationship observed at 1-30 micromoll(-1) Ni (K(m) - 11 micromoll(-1), J(max) - 53 pmolcm(-2)h(-1) in the stomach and K(m) - 42 micromoll(-1), J(max) - 215 pmolcm(-2)h(-1) in the mid-intestine), suggesting mediation by a channel or carrier process. A linear uptake relationship was seen at higher concentrations, indicative of simple diffusion. Ni uptake (at 30 micromoll(-1)) into the blood compartment was significantly reduced in the stomach by high Mg (50 mmoll(-1)), and in the mid-intestine by both Mg (50 mmoll(-1)) and Ca (50 mmoll(-1)). In both regions, kinetic analysis demonstrated reductions in J(max) with unchanged K(m), suggesting non-competitive interactions. Therefore the Mg and Ca content of the food will be an important consideration affecting the availability of Ni.

Ammonia as a stimulant to ventilation in rainbow trout Oncorhynchus mykiss

Ammonia is the third most important respiratory gas in ammoniotelic fish after oxygen and carbon dioxide. We here investigated the effects of elevated plasma ammonia on ventilation in freshwater rainbow trout. Intact trout fitted with indwelling dorsal aortic catheters were given injections (over 5 min) of Cortland saline, isotonic high ammonia solutions (NH(4)HCO(3), (NH(4))(2)SO(4), NH(4)OH at pH 8.0, and NH(4)OH at pH 9.0), and other solutions as controls for acid-base effects, while ventilatory rate (VR) and buccal pressure amplitude (DeltaP(buccal)) were recorded. All high ammonia solutions resulted in immediate elevations of plasma Tamm(a), Pa(NH3), and [NH(4)(+)](a), and increases in ventilatory DeltaP(buccal) and VR to different degrees. However, while Pa(O2) remained constant, in every case there was a confounding change in one or more components of acid-base status (decreases in pH(a) or increases in [HCO(3)(-)](a) or Pa(CO2) in different treatments), although the ventilatory responses to ammonia injections were generally larger than could be explained by changes in acid-base status. Therefore a series was performed in which normal blood perfusion of the gills was replaced by ventral aortic perfusion with either Cortland saline or Cortland saline plus high ammonia in which pH, [HCO(3)(-)], P(CO2), and P(O2) remained unchanged. Although ventilation was depressed in these anaesthetized, spontaneously ventilating preparations, perfusion with high ammonia saline increased DeltaP(buccal). In a final series, trout were infused for 24h with Cortland saline, isotonic NH(4)HCO(3), or isotonic (NH(4))(2)SO(4) solutions. The two ammonia solutions both caused persistent elevations in VR and DeltaP(buccal), together with similar large increases in plasma Tamm(a), Pa(NH3), and [NH(4)(+)](a). As there was no changes in Pa(O2), pH(a), Pa(CO2), or [HCO(3)(-)](a) in the (NH(4))(2)SO(4) infusion series, this, together with the ventral aortic perfusion experiment, provides the most convincing evidence that ammonia stimulates ventilation. We suggest several circumstances (post-feeding, post-exercise) where the role of ammonia as a ventilatory stimulant may have adaptive benefits for O(2) uptake, and propose that ammonia-induced hyperventilation may also facilitate ammonia excretion in rainbow trout.

Using omeprazole to link the components of the post-prandial alkaline tide in the spiny dogfish, Squalus acanthias

After a meal, dogfish exhibit a metabolic alkalosis in the bloodstream and a marked excretion of basic equivalents across the gills to the external seawater. We used the H(+), K(+)-ATPase pump inhibitor omeprazole to determine whether these post-prandial alkaline tide events were linked to secretion of H(+) (accompanied by Cl(-)) in the stomach. Sharks were fitted with indwelling stomach tubes for pretreatment with omeprazole (five doses of 5 mg omeprazole per kilogram over 48 h) or comparable volumes of vehicle (saline containing 2% DMSO) and for sampling of gastric chyme. Fish were then fed an involuntary meal by means of the stomach tube consisting of minced flatfish muscle (2% of body mass) suspended in saline (4% of body mass total volume). Omeprazole pre-treatment delayed the post-prandial acidification of the gastric chyme, slowed the rise in Cl(-) concentration of the chyme and altered the patterns of other ions, indicating inhibition of H(+) and accompanying Cl(-) secretion. Omeprazole also greatly attenuated the rise in arterial pH and bicarbonate concentrations and reduced the net excretion of basic equivalents to the water by 56% over 48 h. Arterial blood CO(2) pressure (Pa(CO(2))) and plasma ions were not substantially altered. These results indicate that elevated gastric H(+) secretion (as HCl) in the digestive process is the major cause of the systemic metabolic alkalosis and the accompanying rise in base excretion across the gills that constitute the alkaline tide in the dogfish.

Regulation of gill transcellular permeability and renal function during acute hypoxia in the Amazonian oscar (Astronotus ocellatus): new angles to the osmorespiratory compromise

Earlier studies demonstrated that oscars, endemic to ion-poor Amazonian waters, are extremely hypoxia tolerant, and exhibit a marked reduction in active unidirectional Na+ uptake rate (measured directly) but unchanged net Na+ balance during acute exposure to low PO2, indicating a comparable reduction in whole body Na+ efflux rate. However, branchial O2 transfer factor does not fall. The present study focused on the nature of the efflux reduction in the face of maintained gill O2 permeability. Direct measurements of 22Na appearance in the water from bladder-catheterized fish confirmed a rapid 55% fall in unidirectional Na+ efflux rate across the gills upon acute exposure to hypoxia(PO2=10–20 torr; 1 torr=133.3 Pa), which was quickly reversed upon return to normoxia. An exchange diffusion mechanism for Na+ is not present, so the reduction in efflux was not directly linked to the reduction in Na+ influx. A quickly developing bradycardia occurred during hypoxia. Transepithelial potential, which was sensitive to water [Ca2+], became markedly less negative during hypoxia and was restored upon return to normoxia. Ammonia excretion, net K+ loss rates, and 3H2O exchange rates(diffusive water efflux rates) across the gills fell by 55–75% during hypoxia, with recovery during normoxia. Osmotic permeability to water also declined, but the fall (30%) was less than that in diffusive water permeability (70%). In total, these observations indicate a reduction in gill transcellular permeability during hypoxia, a conclusion supported by unchanged branchial efflux rates of the paracellular marker [3H]PEG-4000 during hypoxia and normoxic recovery. At the kidney, glomerular filtration rate, urine flow rate, and tubular Na+ reabsorption rate fell in parallel by 70% during hypoxia, facilitating additional reductions in costs and in urinary Na+, K+ and ammonia excretion rates. Scanning electron microscopy of the gill epithelium revealed no remodelling at a macro-level, but pronounced changes in surface morphology. Under normoxia,mitochondria-rich cells were exposed only through small apical crypts, and these decreased in number by 47% and in individual area by 65% during 3 h hypoxia. We suggest that a rapid closure of transcellular channels, perhaps effected by pavement cell coverage of the crypts, allows conservation of ions and reduction of ionoregulatory costs without compromise of O2exchange capacity during acute hypoxia, a response very different from the traditional osmorespiratory compromise.

Maternal and foetal outcomes in pregnant patients with active lupus nephritis

The objective of this study was to determine the impact of lupus nephritis disease activity on maternal and foetal outcomes in pregnant patients with systemic lupus erythematosus (SLE). Medical records of all pregnant patients with SLE treated at our institution between 1976 and 2007 were reviewed. All patients met American College of Rheumatology classification criteria for SLE. Demographic data, history of lupus nephritis, nephritis disease activity and maternal and foetal outcomes of pregnancy were abstracted. Active lupus nephritis was defined as the presence of proteinuria >0.5 g/day and/or active urinary sediment with or without an elevation in serum creatinine (Cr). Quiescent lupus nephritis was confirmed in the presence of proteinuria <0.5 mg/day and inactive urinary sediment. We identified 58 patients with 90 pregnancies. Compared with pregnancies in SLE patients without renal involvement (n = 47), pregnancies in patients with active lupus nephritis (n = 23) were associated with a higher incidence of maternal complications (57% vs 11%, P < 0.001), whereas those with quiescent lupus nephritis (n = 20) were not (35% vs 11%, P = 0.10). Women with active lupus nephritis were more likely to deliver preterm than women without lupus nephritis, median of 34 weeks vs 40 gestational weeks, respectively (P = 0.002) and were more likely to suffer foetal loss (35% vs 9%, P = 0.031). Active, but not quiescent, lupus nephritis during pregnancy is associated with a higher incidence of maternal and foetal complications compared with pregnancies in SLE patients without renal involvement.

Ammonia transport in cultured gill epithelium of freshwater rainbow trout: the importance of Rhesus glycoproteins and the presence of an apical Na+/NH4+ exchange complex

The mechanisms of ammonia excretion at fish gills have been studied for decades but details remain unclear, with continuing debate on the relative importance of non-ionic NH(3) or ionic NH(4)(+) permeation by various mechanisms. The presence of an apical Na(+)/NH(4)(+) exchanger has also been controversial. The present study utilized an in vitro cultured gill epithelium (double seeded insert, DSI) of freshwater rainbow trout as a model to investigate these issues. The relationship between basolateral ammonia concentration and efflux to apical freshwater was curvilinear, indicative of a saturable carrier-mediated component (K(m)=66 micromol l(-1)) superimposed on a large diffusive linear component. Pre-exposure to elevated ammonia (2000 micromol l(-1)) and cortisol (1000 ng ml(-1)) had synergistic effects on the ammonia permeability of DSI, with significantly increased Na(+) influx and positive correlations between ammonia efflux and Na(+) uptake. This increase in ammonia permeability was bidirectional. It could not be explained by changes in paracellular permeability as measured by [(3)H]PEG-4000 flux. The mRNA expressions of Rhbg, Rhcg2, H(+)-ATPase and Na(+)/H(+) exchanger-2 (NHE-2) were up-regulated in DSI pre-exposed to ammonia and cortisol, CA-2 mRNA was down-regulated, and transepithelial potential became more negative. Bafilomycin (1 micromol l(-1)), phenamil (10 micromol l(-1)) and 5-(N,N-hexamethylene)amiloride (HMA, 10 micromol l(-1)) applied to the apical solution significantly inhibited ammonia efflux, indicating that H(+)-ATPase, Na(+) channel and NHE-2 pathways on the apical surface were involved in ammonia excretion. Apical amiloride (100 micromol l(-1)) was similarly effective, while basolateral HMA was ineffective. Pre-treatment with apical freshwater low in [Na(+)] caused increases in both Rhcg2 mRNA expression and ammonia efflux without change in paracellular permeability. These data suggest that Rhesus glycoproteins are important for ammonia transport in the freshwater trout gill, and may help to explain in vivo data where plasma ammonia stabilized at 50% below water levels during exposure to high environmental ammonia ( approximately 2300 micromol l(-1)). We propose an apical ;Na(+)/NH(4)(+) exchange complex' consisting of several membrane transporters, while affirming the importance of non-ionic NH(3) diffusion in ammonia excretion across freshwater fish gills.

Cadmium transport by the gut and Malpighian tubules of Chironomus riparius

Many aquatic insects are very insensitive to cadmium in short-term laboratory studies. LC50 values for larvae of the midge Chironomus riparius are over 25,000 times the Criterion Maximum Concentration in the United States Environmental Protection Agency (U.S. EPA (2000)) species sensitivity distribution (SSD). Excretion or sequestration of cadmium may contribute to insensitivity and we have therefore examined cadmium transport by isolated guts and renal tissues of C. riparius larvae. Regional differences of Cd transport along the gut were identified using a Cd(2+)-selective microelectrode in conjunction with the Scanning Ion-Selective Electrode Technique (SIET). Cd is transported into the anterior midgut (AMG) cells from the lumen and out of the cells into the hemolymph. The transport of Cd from the gut lumen to the hemolymph exposes other tissues such as the nervous system and muscles to Cd. The gut segments which remove Cd from the hemolymph at the highest rate are the posterior midgut (PMG) and the ileum. In addition, assays using an isolated Malpighian (renal) tubule preparation have shown that the Malpighian tubules (MT) both sequester and secrete Cd. For larvae bathed in 10 micromol l(-1) Cd, the tubules can secrete the entire hemolymph burden of Cd in approximately 15 h.

Morphology of the rectal gland of the spiny dogfish (Squalus acanthias) shark in response to feeding

The morphology of the rectal gland was examined in spiny dogfish ( Squalus acanthias L, 1758) sharks fasted (1 week) or 6 and 20 h postfeeding. The morphology of the fasted gland showed a pattern reflecting a dormant physiology, with thick gland capsule, thick stratified epithelium, and secretory parenchyma with tubules of small diameter and lumen. The secretory cells of the tubular epithelium were enlarged and irregularly shaped with abnormally condensed or highly vacuolized cytoplasm containing numerous lysosomes. Early-stage apoptotic cells were not uncommon. Secretory cells showed signs of low activity, e.g., mitochondria with weakly stained matrix and small cristae, poorly branched infoldings of basolateral membranes, and microvesicle-free subapical cytoplasm. All characteristics examined changed significantly upon feeding, consistent with increased salt and fluid secretion: the outer capsule muscle layer and the stratified epithelium decreased in diameter; the tubules enlarged; the secretory cells showed extensive development of the basolateral membrane, more mitochondria, and abundant apical microvesicles. Secretory cell apical surface was increased. The minor differences between morphology in 6 and 20 h postfeeding indicated that changes took place rapidly and were complete by 6 h. Our results are discussed in the context of prior studies of metabolism, proteomics, and cellular pathways of gland activation.

Sperm performance under hypoxic conditions in the intertidal fish Porichthys notatus

Hypoxia (low oxygen) exposure generally leads to decreased reproductive capacity, exhibited by reductions in testicular mass, reproductive hormones, and sperm swimming speed. However, in many fish species, reproduction occurs either periodically or exclusively under hypoxic conditions. In this study we assessed how hypoxia influences sperm performance in the plainfin midshipman ( Porichthys notatus Girard, 1854), a species that lives in intertidal nests that become hypoxic during low tides. We exposed sperm from the same male to normoxic or hypoxic conditions and compared sperm characteristics and oxygen consumption between treatments. Sperm exposed to hypoxic water swam faster and consumed more oxygen than sperm swimming in normoxic conditions. Sperm swimming speed was positively related with oxygen consumption. For each male, the percentage of motile spermatozoa did not differ between treatments, suggesting that the same number of sperm were active but their performance was dependent on the dissolved oxygen content in the water. We discuss the implications of our results in the context of sperm competition and fertilization success under hypoxic conditions.

Toxicity of dissolved Cu, Zn, Ni and Cd to developing embryos of the blue mussel (Mytilus trossolus) and the protective effect of dissolved organic carbon

Marine water quality criteria for metals are largely driven by the extremely sensitive embryo-larval toxicity of Mytilus sp. Here we assess the toxicity of four dissolved metals (Cu, Zn, Ni, Cd) in the mussel Mytilus trossolus, at various salinity levels while also examining the modifying effects of dissolved organic carbon (DOC) on metal toxicity. In 48 h embryo development tests in natural seawater, measured EC50 values were 6.9-9.6 microg L(-1) (95% C.I.=5.5-10.8 microg L(-1)) for Cu, 99 microg L(-1) (86-101) for Zn, 150 microg L(-1) (73-156) for Ni, and 502 microg L(-1) (364-847) for Cd. A salinity threshold of >20 ppt (approximately 60% full strength seawater) was required for normal control development. Salinity in the 60-100% range did not alter Cu toxicity. Experimental addition of dissolved organic carbon (DOC) from three sources reduced Cu toxicity; for example the EC50 of embryos developing in seawater with 20 mg C L(-1) was 39 microg Cu L(-1) (35.2-47.2) a 4-fold increase in Cu EC50. The protective effects of DOC were influenced by their distinct physicochemical properties. Protection appears to be related to higher fulvic acid and lower humic acid content as operationally defined by fluorescence spectroscopy. The fact that DOC from freshwater sources provides protection against Cu toxicity in seawater suggests that extrapolation from freshwater toxicity testing may be possible for saltwater criteria development, including development of a saltwater Biotic Ligand Model for prediction of Cu toxicity.

Increased gene expression of a facilitated diffusion urea transporter in the skin of the African lungfish (Protopterus annectens) during massively elevated post-terrestrialization urea excretion

The full-length cDNA sequence of a putative urea transporter (lfUT) of the facilitated diffusion UT-A type has been cloned from the African lungfish Protopterus annectens. The lfUT cDNA is 1990 bp in length and its open reading frame encodes a 409 amino acid long protein, with a calculated molecular mass of 44,723 Da. The sequence is closest to those of amphibians ( approximately 65% amino acid homology), followed by mammals and elasmobranchs ( approximately 60%), and then teleosts ( approximately 50%). lfUT was clearly expressed in gill, kidney, liver, skeletal muscle and skin. Upon re-immersion in water after 33 days of air exposure ('terrestrialization'), lungfish exhibited a massive rise in urea-N excretion which peaked at 12-30 h with rates of 2000-5000 micromol-N kg(-1) h(-1) (versus normal aquatic rates of <130 micromol-N kg(-1) h(-1)) and persisted until 70 h. This appears to occur mainly through the skin. Total 'excess' urea-N excretion amounted to approximately 81,000-91,000 micromol-N kg(-1) over 3 days. By real-time PCR, there was no difference in lfUT expression in the ventral abdominal skin between aquatic ammoniotelic controls and terrestrialized lungfish immediately after return to water (0 h), and no elevation of urea-N excretion at this time. However, skin biopsies revealed a significant 2.55-fold elevation of lfUT expression at 14 h, coincident with peak urea-N excretion. At 48 h, there was no longer any significant difference in lfUT mRNA levels from those at 0 and 14 h, or from aquatic fed controls. In accordance with earlier studies, which identified elevated urea-N excretion via the skin of P. dolloi with pharmacology typical of UT-A carriers, these results argue that transcriptional activation of a facilitated diffusion type urea transporter (lfUT) occurs in the skin during re-immersion. This serves to clear the body burden of urea-N accumulated during terrestrialization.

Do you smell what I smell? Olfactory impairment in wild yellow perch from metal-contaminated waters

In this study, we sampled yellow perch from three lakes along a metal-contamination gradient and examined their olfactory ability in response to conspecific chemical alarm cues and metal-binding characteristics of their olfactory epithelium (OE). We measured the electrophysiological response at the OE, tested their antipredator behaviour and measured neuronal density at the olfactory rosette and bulb. Yellow perch from contaminated lakes exhibited significantly larger electrophysiological responses to alarm cues than clean lake fish, but showed no antipredator behaviour contrary to clean lake fish. Neuron density did not differ at either the olfactory rosette or bulb between clean and contaminated fish. Unlike fishes raised under laboratory or aquaculture settings, fish from contaminated lakes possessed a functional OE after metal exposure, but similar to laboratory/aquaculture fishes, yellow perch did not exhibit olfactory-mediated behaviours. Thus, wild fish from contaminated lakes can detect chemical stimuli but olfactory signal processing is disrupted which could alter ecological functioning.

The effect of water chemistry on the acute toxicity of nickel to the cladoceran Daphnia pulex and the development of a biotic ligand model

The goal of this study was to evaluate the influence of water chemistry parameters on the acute toxicity of waterborne Ni to Daphnia pulex in soft waters and using this information to develop a biotic ligand model. The effects of Ca, Mg, Na, K, Cl, pH (two differently buffered sets) and natural organic matter (NOM) from two sources were evaluated in standardized 48h acute toxicity tests. Increases in Ca2+ had a protective effect on Ni toxicity, suggesting that this ion competes with Ni at the site of biological uptake. Increased waterborne Mg2+ also reduced Ni toxicity, but to a lesser degree compared with Ca2+. EC50 values increased at higher pH when the organic buffer 3-morpholinepropanesulfonic acid was used to adjust test pH, however in tests series where pH was varied using HCO(3)(-) the results were equivocal. Other testing showed that Na, K and Cl did not influence the toxicity response of D. pulex to Ni. Complexation of Ni by NOM reduced toxicity but Nordic Reservoir NOM was much more protective compared to Suwannee River NOM. Geochemical modeling of organic matter complexation of Ni was done using the HydroQual Biotic Ligand Model (BLM ver. 2.3.3; research mode) and the Windermere Humic Aqueous Model (WHAM ver 6.0). Results showed dramatic differences between the two models in dissolved organic matter complexation. Modelling of Ni geochemistry for test solutions other than those containing NOM showed consistent and minor differences between the WHAM and the BLM. The latter model was used to develop a comprehensive prediction model of Ni toxicity. logK values developed for competitive cationic effects showed that Ca and Mg have a much higher protective effect in soft water compared to models developed for Daphnia magna in hard water. The BLM developed for this species in soft water provided good predictions of toxicity across a wide range of Ni concentrations but also highlighted the need for an improved understanding of the effects of NOM and pH on Ni toxicity in soft waters.

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.

A matter of potential concern: natural organic matter alters the electrical properties of fish gills

Natural organic matter (NOM) is an important constituent of aquatic environments; however, its influence on aquatic biota remains poorly studied. In the current study, NOM was isolated from nine different sites in southern Ontario, Canada, by the on-site treatment of water by reverse osmosis, followed by cation exchange. NOM from each site was reconstituted to 10 mg of C/L and pH 7.0 and exposed to either adult rainbow trout implanted with indwelling catheters or to in vitro primary cultures of the gill epithelium grown on semipermeable membranes. In both the in vivo and in vitro preparations, NOM was found to hyperpolarize transepithelial potential (TEP), with the magnitude of this change correlating extremely well to the absorptivity of the NOM at 340 nm, which is an index of its aromaticity. Gill hyperpolarization appeared to be independent of Ca2+ complexation by the NOM in all but two samples tested. We argue that NOM has direct actions on the ionic transport and/or permeability properties of fish gills. While NOM effects on the bioavailability of contaminants are well-known, NOM actions on such fundamental physiological properties of the gills have previously been overlooked. These may be of comparable or greater magnitude than commonly reported for other water-quality variables (e.g., hardness, pH, salinity) and therefore of critical importance in ecological understanding and risk assessment.

The effects of CO2 and external buffering on ammonia excretion and Rhesus glycoprotein mRNA expression in rainbow trout

Rhesus (Rh) proteins were recently characterized as ammonia gas (NH(3)) channels. Studies indicate, however, that Rh proteins also facilitate CO2 transport in a green alga and in human erythrocytes. Previously, we reported that Rh mRNA expression in various rainbow trout tissues responded to high environmental ammonia. To determine whether or not Rh proteins may also be involved in CO2 transport in rainbow trout, we examined the effects of a 12 h exposure to external hypercapnia (1% CO2 in air) on Rh mRNA expression in the gill, skin and erythrocytes. External hypercapnic conditions lowered the water pH and facilitated ammonia excretion; therefore, we also studied the effects of hypercapnia and normocapnia in the presence of 10 mmol l(-1) Hepes-buffered water. Hepes treatment prevented water acidification, but resulted in elevated plasma ammonia levels and reduced ammonia excretion rates. Hypercapnia exposure without buffering did not elicit changes in Rh mRNA expression in the gill or skin. However, Rhcg2 mRNA expression was downregulated in the gills and upregulated in the skin of both normocapnia- and hypercapnia-exposed fish in Hepes-buffered water. mRNA expression of a newly cloned Rhbg2 cDNA was downregulated in the skin of fish exposed to buffered water, and Rhag mRNA expression in erythrocytes was decreased with exposure to normocapnia in buffered water but not with hypercapnia exposure in either buffered or unbuffered water. With the aid of Hepes buffering, we were able to observe the effects of both CO2 and ammonia on Rh mRNA expression. Overall, we conclude that high CO2 did not directly elicit changes in Rh mRNA transcription levels in the gill and skin, and that the changes observed probably reflect responses to high plasma ammonia, mirroring those in trout exposed to high environmental ammonia. Therefore a dual function for gill and skin Rh proteins in CO2 and ammonia transport is not evident from these results. Rhag expression, however, responded differentially to high CO2 and high ammonia, suggesting a possible dual role in the erythrocytes.

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.