The ionoregulatory responses to hypoxia in the freshwater rainbow trout Oncorhynchus mykiss.

We utilized the rainbow trout, a hypoxia-intolerant freshwater teleost, to examine ionoregulatory changes at the gills during hypoxia. Progressive mild hypoxia led first to a significant elevation (by 21%) in J(Na)(influx) (measured with 22Na), but at 4-h hypoxia when PCO2 reached approximately 110 mmHg, there was a 79% depression in J(Na)(influx). Influx remained depressed during the first hour of normoxic recovery but was restored back to control rates thereafter; there were no significant changes in J(Na)(efflux) or J(Na)(net).

The role of the kidney in compensating the alkaline tide, electrolyte load, and fluid balance disturbance associated with feeding in the freshwater rainbow trout, Oncorhynchus mykiss.

The effect in freshwater rainbow trout of digesting a commercial pellet meal on the renal handling of water, ions and acid-base equivalents was investigated through urine collection over a 48 h period following meal ingestion. The glomerular filtration rate (GFR) and urine flow rate (UFR) were reduced in fed fish between 12 and 24h following the meal, likely reflecting a loss of endogenous water across the gastric epithelium as a result of ingesting dry, ion-rich food pellets. The kidney was also responsible for the excretion of some excess dietary Ca(2+), and, to a much lesser extent, Na(+) and Cl(-), while the urinary excretion of K(+) was unaffected.

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.

The stress response of the highly social African cichlid Neolamprologus pulcher.

In group-living species, dominant individuals are frequently aggressive toward subordinates, and such dominant aggression can lead to chronic stress, higher glucocorticoid levels, and decreased fitness for subordinates. However, in many cooperatively breeding species, it is surprisingly the dominants rather than the subordinates that exhibit higher levels of glucocorticoids, a possible consequence of the demands of maintaining high social rank and socially suppressing the reproduction of other group members. This study investigates the relationship between social status and circulating plasma cortisol in groups of the cooperatively breeding African cichlid Neolamprologus pulcher.

The role of size in synchronous air breathing of Hoplosternum littorale.

Synchronized air breathing may have evolved as a way of minimizing the predation risk known to be associated with air breathing in fish. Little is known about how the size of individuals affects synchronized air breathing and whether some individuals are required to surface earlier than necessary in support of conspecifics, while others delay air intake. Here, the air-breathing behavior of Hoplosternum littorale held in groups or in isolation was investigated in relation to body mass, oxygen tensions, and a variety of other physiological parameters (plasma lactate, hepatic glycogen, hematocrit, hemoglobin, and size of heart, branchial basket, liver, and air-breathing organ [ABO]).

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.

The influence of feeding and fasting on plasma metabolites in the dogfish shark (Squalus acanthias).

Dogfish sharks are opportunistic predators, eating large meals at irregular intervals. Here we present a synthesis of data from several previous studies on responses in plasma metabolites after natural feeding and during prolonged fasting (up to 56days), together with new data on changes in plasma concentrations of amino acids and non-esterified fatty acids. Post-prandial and long-term fasting responses were compared to control sharks fasted for 7days, a typical inter-meal interval.

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.

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.

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)).

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.

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.

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 P(O(2)), indicating a comparable reduction in whole body Na(+) efflux rate. However, branchial O(2) transfer factor does not fall. The present study focused on the nature of the efflux reduction in the face of maintained gill O(2) permeability.

mRNA expression analysis of the physiological responses to ammonia infusion in rainbow trout.

We recently reported that tissue levels of Rhesus (Rh) mRNA in rainbow trout changed in response to high-external ammonia (HEA). To investigate whether or not these changes could be due to elevated plasma ammonia levels, we infused rainbow trout for 12 h with 140 mmol L(-1) NH(4)HCO(3), or with 140 mmol L(-1) NaCl as a control for the effects of infusion. We also analyzed the effects of dorsal aortic catheterization alone, without infusion.

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%).

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.

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.

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.

TEP on the tide in killifish (Fundulus heteroclitus): effects of progressively changing salinity and prior acclimation to intermediate or cycling salinity.

Transepithelial potentials (TEP) were measured in killifish, acclimated to freshwater (FW), seawater (SW), 33% S: W or cycling salinities relevant to tidal cycles in an estuary, and subsequently subjected to salinity changes in progressive or random order. Random compared to progressive salinity changes in an upward or downward direction in FW- and SW-acclimated fish, respectively, did not greatly influence responses to salinity change. Fish acclimated to SW or 33% SW as well as those acclimated to cycling salinities behaved similarly (TEP more positive than +15 mV in 100% SW, decreasing to approximately 0 mV at 20-40% SW, and more negative than -30 mV in FW).

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.

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.

Dietary iron alters waterborne copper-induced gene expression in soft water acclimated zebrafish (Danio rerio).

Metals like iron (Fe) and copper (Cu) function as integral components in many biological reactions, and, in excess, these essential metals are toxic, and organisms must control metal acquisition and excretion. We examined the effects of chronic waterborne Cu exposure and the interactive effects of elevated dietary Fe on gene expression and tissue metal accumulation in zebrafish. Softwater acclimated zebrafish exposed to 8 microg/l Cu, with and without supplementation of a diet high in Fe (560 vs.

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.

Water balance and renal function in two species of African lungfish Protopterus dolloi and Protopterus annectens.

The basic physiology of water balance and kidney function was characterized in two species of African lungfish, Protopterus dolloi and Protopterus annectens. Diffusive water efflux rate constants were low (0.13 h(-1)-0.