Artificial Soft Water Research Articles

Performance recovery of proton exchange membrane electrolyzer degraded by metal cations contamination

Hydrogen production from renewable electricity offers an eco-friendly alternative to fossil fuels. Proton exchange membrane (PEM) electrolysis is a well-known method for this purpose. Studies have primarily focused on reducing costs of noble catalysts, improving efficiency, managing system degradation, and addressing membrane thinning caused by contaminated cations. However, techniques for PEM recovery post-degradation are still under development. This study investigated the effects of cations on PEM cells using artificial soft water, and analyzed two recovery methods to restore cell performance. Our findings indicate a significant rise in cell operating voltage and a decrease hydrogen production over 8 h of operation with soft water. After introducing both recovery methods, the initial operating value was reinstated in both cases. Only nitric acid treatment, however, achieved hydrogen production levels comparable to those of ultrapure water.

Life in acid: interactive effects of pH and natural organic acids on growth, development and locomotor performance of larval striped marsh frogs (Limnodynastes peronii)

The low pH of naturally acidic aquatic environments is the result of soft-water with low buffering capacity and high concentrations of natural organic acids. Our current understanding of the influence of pH on aquatic organisms is largely limited to laboratory studies conducted under controlled conditions with little incorporation of these organic acids. Recent studies suggest natural organic acids may influence the physiology of aquatic species independent of low pH. We examined the effects of pH and varying concentrations of natural wallum water, which is high in organic acids on the hatching success, growth and locomotor performance of larval striped marsh frogs (Limnodynastes peronii). Based on previous studies, we predicted that the detrimental effects of low pH would be further exacerbated by higher concentrations of naturally occurring organic acids (high concentrations of wallum water). In artificial soft-water, embryos experienced both reduced growth and reduced survival when exposed to low pH. However, greater concentrations of natural organic acids did not exacerbate these effects of low pH on growth and development. Instead, we found some evidence that the natural organic acids within wallum water improved growth and swimming performance across all pH treatments. Using path analyses to investigate the effects of pH and natural organic acid concentration on burst swimming performance, we found performance was directly affected by both body length and organic acid concentration. Our data further highlight our limited understanding of the importance of natural organic acids for aquatic organisms and the need to incorporate greater ecological relevance into these studies.

Lethal body residue of chlorophenols and mixtures of chlorophenols in benthic organisms.

The lethal body residue (LBR) of a few chlorophenol congeners were measured in the oligochaete worm Lumbriculus variegatus, and the LBR of pentachlorophenol was measured also in a midge, Chironomus riparius larvae. LBR is defined as the concentration of the compound in the organism, on molar basis, to cause death, and the LBR(50) is defined as the calculated LBR value to cause a 50% mortality in population after a given time. Groups of 30 or 40 organisms were exposed to different chlorophenol concentrations in artificial soft fresh water to achieve differential mortality. Exposure times were either 24 h or 48 h. In addition to exposures with individual congeners, mixtures of chlorophenols were also tested. After each exposure, the surviving organisms were collected and the body burden of chlorophenols was measured by gas chromatography with electron capture detection. The measured body burden was related to the percent mortality in the group. The trichlorophenols and pentachlorophenol have a 48-h LBR(50) of 0.45-0.66 micromol/g wet weight in L. variegatus. The 48-h LBR(50) of pentachlorophenol for C. riparius was 0.15 micromol/g wet weight, indicating a slight difference in the sensitivity of these two species. The 48-h LBR(50) of 2,3,4,6-tetrachlorophenol is 0.91 micromol/g wet weight, and the value for 2,6-dichlorophenol is 1.2 micromol/g wet weight in L. variegatus. The 48-h LBR(50)s of the chlorophenol mixtures ranged from 0.50 to 0.83 micromol/g wet weight, demonstrating an additive toxicity.

Detrimental effects associated with trace element uptake in lake chubsuckers (Erimyzon sucetta) exposed to polluted sediments.

Lake chubsuckers (Erimyzon sucetta) were exposed to coal ash-polluted sediments under conservative experimental conditions (filtered artificial soft water and abundant uncontaminated food). After 4 months of exposure, fish grazing the polluted sediments had significantly elevated body burdens of Se, Sr, and V. Selenium levels were particularly elevated, reaching mean whole body concentrations of 5.6 microg/g dry mass by the end of experimental manipulations. Twenty-five percent of fish exposed to pollutants died during the study. All surviving fish exposed to ash exhibited substantial decreases in growth and severe fin erosion. Total nonpolar lipids were two times higher in fish from the control treatment, but percent lipid did not differ between treatments. Because fish were presented with the same amount of food during the study, it appears fish exposed to ash utilized more energy for daily activities and/or were less efficient at converting available energy to tissues for growth and storage. The results were particularly interesting because we were unable to detect differences in standard metabolic rate (SMR) of fish between treatments. Increased energy expenditures not detectable in estimates of maintenance based on SMR, such as costs of digestion or activity, may have contributed to decreased energetic efficiency. Our findings corroborate previous studies which have documented the toxicity of ash-derived pollutants in fish.

Branchial Ionic Flux Responses in Rainbow Trout to Chloramine-T after Acclimation to Different Levels of Water Hardness

Abstract Whole-body unidirectional and net Na+ and Cl– fluxes were determined in rainbow trout Oncorhynchus mykiss exposed to chloramine-T (9 mg/L) alone or in combination with 17 mmol NaCl/L (0.1 % weight per volume, w/v) after acclimation to either city of Ottawa tap water (TW: Na+ 0.121 ± 0.004 mmol/L; K+ 0.015 ± <0.001 mmol/L; Ca2+ 0.351 ± 0.004 mmol/L; Cl– 0.141 ± 0.002 mmol/L) or artificial soft water (ASW: Na+ 0.043 ± 0.003 mmol/L; K+ 0.005 ± <0.001 mmol/L; Ca2+ 0.063 ± 0.002 mmol/L; Cl– 0.026 ± 0.002 mmol/L). Preexposure fluxes revealed that ASW-acclimated fish had reduced rates of Na+ uptake and efflux compared with TW-acclimated fish. However, rates of Cl– uptake among ASW-acclimated fish were comparable with those of TW-acclimated fish. Exposure to chloramine-T in TW resulted in significant increases in the Cl– efflux, giving rise to a significant and negative net flux. Exposure of ASW-acclimated fish to chloramine-T caused a significant negative increase in the Na+ efflux and net flux but only...

Plasma ammonia concentration in brown trout in soft acidic water and its relationship to decreased swimming performance

Adult brown trout (300&shy;600 g) were acclimated for 2 weeks to an artificial soft water (Ca2+, 50 &micro;mol l-1) and maintained at either 5 &deg;C (October to March) or 15 &deg;C (May to August). Following insertion of a cannula into the dorsal aorta under MS-222 anaesthesia and a recovery period of 2 days, the fish were exposed to a 4 day episode of sub-lethal copper levels at pH 5 or kept at control conditions of pH 7 without copper. The copper concentrations had been predetermined by toxicity testing and were approximately 0.47 &micro;mol l-1 at 5 &deg;C and 0.08 &micro;mol l-1 at 15 &deg;C. At 5 &deg;C, a group of fish was also exposed to approximately 0.08 &micro;mol l-1 copper at pH 5. Plasma total ammonia (Tamm) concentration was significantly elevated by exposure to copper and pH 5. In resting trout exposed to the appropriate sub-lethal copper concentration at pH 5, Tamm was six and 7.5 times greater at 5 and 15 &deg;C, respectively, than those of control trout at the respective temperatures. Although unconfirmed, an elevation of ammonia production alone seems unlikely to account for such substantial increases. From previous studies, there is little evidence of impairment of respiratory gas exchange in trout exposed to these copper concentrations and yet, in the acidic test waters, the gradient of NH3 partial pressure between fish and water was 5.5&shy;6 times greater than that under control conditions. Swimming performance determined by the critical swimming speed (Ucrit) was reduced by copper and acid exposure, and a significant relationship existed between Ucrit and the plasma ammonia concentration of exercised trout. Ammonium ions influence several key enzymes involved in energy metabolism, and elevated ammonia levels might, therefore, reduce the capacity of muscle to exercise. Alternatively, ammonia may have affected the nervous coordination of exercise either centrally or by disrupting peripheral motor innervation.

Exposure of brown trout, Salmo trutta, to sub-lethal copper concentrations in soft acidic water and its effect upon sustained swimming performance

Toxicity tests were performed to determine the 96 h sub-lethal copper concentration at pH 5 (SLCC) for adult brown trout acclimated to 5 °C (Oct.–Mar.) or 15 °C (May–Aug.) in an artificial softwater (Ca 2+ 50 μmol l −1). These were found to be 0.47 and 0.08 μmol l −1 Cu 2+ at 5 and 15 °C respectively. Routine oxygen consumption (M o 2 ) and critical swimming speed (Ucrit) of groups of trout exposed to the SLCC for each temperature were measured and compared to trout maintained in the absence of copper and at pH 7. At 5 °C, an additional group was exposed to the summer copper level of 0.08 μmol l −1 Cu 2+ at pH 5. At the end of each experiment, samples of arterial blood were taken from the dorsal aorta via chronically indwelling cannulae. Copper exposure in acidic water significantly reduced swimming performance. Trout exposed to 0.08 μmol l −1 Cu 2+ at pH 5 achieved a critical swimming speed some 25–50% slower than control trout with no significant temperature effect. Of the six winter trout exposed to 0.47 μmol l −1 Cu 2+ at pH 5, only one swam steadily at the lowest test speed of 0.3 m s −1, the remainder achieving at most a brief burst of activity. Earlier workers suggested that observed increases in aerobic maintenance costs and decreased maximum metabolism arose from copper-induced inefficiencies in ionoregulation and gas exchange and reduced Ucrit to be a consequence of this lower scope for activity. In the present study, plasma sodium and chloride concentrations were reduced some 25–35%, regardless of acclimation temperature or copper concentration. The routine M o 2 of trout exposed to the SLCC at either temperature was elevated (by 72% and 38% at 5 and 15 °C respectively). However, there was no change in that of winter trout exposed to only 0.08 μmol l −1 Cu 2+ at pH 5 although their swimming performance was also reduced. More significantly, there were no changes in the blood oxygen content or lactate concentration of exercised trout at any copper concentration as might be expected if M o 2max was limited by an impaired oxygen uptake. There were, however, some effects of copper and acid exposure, such as increases in haemoglobin and plasma protein concentrations, which may have elevated blood viscosity and which could have led to a disruption of oxygen transport to the tissues. Although the occurrence and magnitude of these effects were not consistent between treatment groups, there is some evidence for a tissue hypoxia from a parallel study.

The Relationship Between Intracellular pH and Swimming Performance of Brown Trout Exposed to Neutral and Sublethal pH

ABSTRACT Adult brown trout were acclimated for 2–4 weeks to artificial soft water ([Ca2+] 25 μmol l−1) at neutral pH and at summer (15°C) temperature. During this period they swam against a current of approximately 0.25 ms −1. They then had their dorsal aorta cannulated and were exposed to neutral or sublethal pH (4.5) for 4 days in still water. After 4 days of exposure to sublethal pH, critical swimming speed (Ucrit) was 35% lower than that for fish at neutral pH. There were significant increases in arterial and in blood lactate concentrations at Ucrit compared with the values in resting fish at neutral pH and these led to significant reductions in plasma pH. There were no such changes in fish at sublethal pH. There were no significant changes in intracellular pH (pHi) of red blood cells at Ucrit, probably as a result of increases in the levels of plasma catecholamines. There were significant reductions in pHi of red and white muscle fibres at Ucrit. It is argued that these values were not as low in the white fibres as those seen in previous studies after fish have been chased to exhaustion and, therefore, that the fish in the present study were not completely exhausted, although they would no longer swim at a steady speed. As pHi of the red muscle was the same at Ucrit for fish at neutral and at sublethal pH, it is suggested that Ucrit (fatigue) coincides with a particular pHi of the red muscles and possible mechanisms are discussed.

Branchial Morphological and Endocrine Responses of Rainbow Trout (Oncorhynchus mykiss) to a Long-Term Sublethal Acid Exposure In Which Acclimation Did Not Occur

Changes in branchial morphology and in plasma Cortisol, adrenaline, and noradrenaline were quantified throughout an 81 -d exposure of rainbow trout (Oncorhynchus mykiss) to sublethal acidity (pH 4.8) in artificial soft water and after a 5-h acid challenge (pH 4.0) of naive fish and 81-d acid-preexposed fish. Changes in branchial morphology at pH 4.8 were generally very mild and characterized by slight increases in filamental mucous cells and decreases in lamellar mucous cells. Chloride cell numbers and branchial Na+–K+- and total ATPase activities did not change. The filamental epithelium thickened, but the water–blood diffusion distance in the lamellae decreased during chronic exposure. Cortisol was significantly elevated throughout whereas catecholamines exhibited relatively little response. Response to acute pH 4.0 challenge was similar in naive and 81-d acid-exposed fish: epithelial damage, increase in visible mucous cells, loss of chloride cells by necrosis, and high cortisol levels but no changes in lamellar or filamental epithelial thickness, diffusion distance, ATPase activities, or catecholamine levels. Previously reported physiological data from these same trout demonstrated that sensitization rather than acclimation had occurred. Therefore, these observations support the view that acclimation does not occur in the absence of significant branchial damage and repair.

Effects of six trace metals on calcium fluxes in brown trout (Salmo trutta L.) in soft water

Calcium fluxes were measured simultaneously in brown trout fry maintained in an artificial soft water medium of [Ca] 20 mumol.1(-1) and pH 5.6, and exposed to each of six trace metals (Al, Cu, Fe, Ni, Pb, and Zn). The trace metal concentrations represented typical and maximum levels found in acid waters experiencing declining fishery status. In the absence of trace metals, evidence is presented which suggests that ca. 91% of Ca taken up from the external medium was by extraintestinal active transport. Calcium efflux was stimulated by both concentrations of Al, Cu, Fe, and Pb. Efflux was also stimulated by [Ni] 170 nmol.1(-1) and [Zn] 3000 nmol.1(-1). In some cases, response to increased efflux was stimulation of influx. Lack of stimulation of influx resulted in negative net Ca fluxes. Net Ca losses were recorded at both concentrations of Al, Pb, and Ni, lower concentrations only of Fe, and higher concentrations only of Cu and Zn.

Episodic exposure to acid and aluminium in soft water: survival and recovery of brown trout,Salmo trutta L.

Yolk-sac fry, swim-up fry and 1–2 yr juveniles of brown trout, Sulmo trutta L., were exposed to episodes of aluminium and low pH, maximum aluminium concentration 12 μmol l−1 (323 μg l−1), minimum pH 4.5, total duration up to 54 h (yolk-sac fry) or up to 78 h (swim-up fry and juveniles), in an artificial soft water medium, [Ca] 20 μmol l−1 (0–8 mg l−1) (nominal baseline: pH 5.6, zero aluminium concentration). Yolk-sac fry mortality was nil or very low. A marked increase in susceptibility, with high mortalities, occurred when the yolk was fully absorbed. Mortality of juveniles exposed to two successive episodes was lower than would have been expected on the basis of comparisons with mortalities in single episodes, and mortality declined as the interval between the two episodes was increased. Disturbance of sodium, potassium or calcium balance or gill damage in surviving yolk-sac fry or juveniles was still evident 5 to 6 days after the end of a single episode.

Role of Organic Complexation in the Toxicity of Aluminum to Rana pipiens Embryos and Bufo americanus Tadpoles

This study investigated the influence of naturally occurring organic compounds on the survival of amphibian embryos and larvae in acidic, aluminum contaminated water. A series of laboratory tests were conducted which measured aluminum toxicity in artificial soft water (ASW) diluted with varying amounts of pond water which contained dissolved organic compounds. At pH 4.5 for tadpoles of Bufo americanus and pH 4.8 for embryos of Rana pipiens, the organic compounds (DOC 5.7 to 16.2 mg∙L−1) complexed the aluminum and thus increased the LC50 for total aluminum by more than two fold. At pH 4.2, 100% ASW and the four dilutions of pond water were toxic to R. pipiens embryos (75–96% mortality), in contrast to higher pH's, aluminum ameliorated acid toxicity which resulted in a 26% reduction in mortality in 100% ASW at 250 mg∙L−1 total aluminum. Although the organic compounds in the pond water also complexed aluminum at pH 4.2, protective levels of labile aluminum [Formula: see text] were still present at 450 μg∙L−1 total aluminum. However, at a given level of labile aluminum in pH 4.2 water, pond water was more toxic to embryos than ASW. At pH 4.2, pond water without added Al was also significantly more toxic to embryos than 100% ASW with 0 μg∙L−1 Al. Toxicity tests using purified humic and fulvic acid sugested that these compounds may be the toxic agents in high dissolved organic carbon (DOC) pond water.

The effects of water hardness upon the uptake, accumulation and excretion of zinc in the brown trout, Salmo trutta L.

The effects of water hardness (9 and 220 mgl−1 as CaCO3) upon zinc exchange in brown trout exposed to 0.77 μmol Zn 1−1 have been investigated using artificial soft water (&lt;49.9 μmol Ca l‐1, &lt;40.1 μmol Mg 1−1) and mains hard water (1671.7 μmol Ca 1−1, 493.6 μmol Mg 1−1) of known composition. Both hard and soft water‐adapted fish exhibited a bimodal pattern of net zinc influx. Net zinc influxes during both fast and slow uptake phases were significantly greater (P&lt;0.001) in soft (82.9 and 6.2 μmol Zn 100 g−1 h−1) than in hard water (46.3 and 2.4 μmol Zn 100 g h−1). Zinc efflux (‐ 0.2 μmol Zn 100 g−1 h−1) was enhanced only in hard water during the slow net influx phase.Brown trout exposed to zinc in hard water and placed in metal‐free media exhibited a greater net efflux (‐ 25.6 μmol Zn 100 g−1 h−1) of the metal than did fish in soft water (‐4.2 μmol Zn 100 g−1 h−1) treated in the same manner. Tissue 65Zn activities reflected both the differences in uptake and excretion rates of the metal between hard and soft water fish. During zinc exposure (0.77 μmol Zn 1−1) high water hardness reduced tissue burdens of the metal by reducing net branchial influx, and enhancing efflux of the metal in hard water fish.

The effects of acid water and aluminium on the embryonic development of the common frog, Rana temporaria

A decline in recent decades in the status of Rana temporaria in the British Isles has been attributed to a number of factors, mostly relating to increased urbanization. Acidification has recently been suggested as a factor which could affect R. temporaria populations in certain areas.The effects of acid water and aluminium on the embryonic development of R. temporaria were investigated using eggs obtained by artificial fertilization from frogs caught in two widely separated areas; an upland area (acidic ponds) and a lowland area (circumneutral ponds). The eggs were kept in artificial soft water at either pH 4.5 or pH 6.0 and with aluminium concentrations covering the range measured in water from the acidic ponds.The survival of embryos to normal free‐swimming larvae was not affected by water pH in the absence of aluminium. Increasing aluminium concentrations reduced the survival of lowland embryos in circumneutral water, but upland embryos were unaffected. However, in acidic water the survival of embryos from both areas decreased with increasing aluminium concentrations. Embryos which did not survive either died early in development, or developed gross abnormalities, or were constricted in the perivitelline membrane and failed to hatch. The body length of surviving larvae was decreased by both increasing aluminium concentrations and low pH, probably owing to a reduction in growth rate rather than development rate. The body length of larvae from upland ponds was decreased less than that of lowland larvae in acidic water, suggesting a greater acid tolerance in embryos from acidic ponds.Reduced embryo survival, sublethal effects, such as reductions in embryonic growth rate, and indirect ecological effects may affect recruitment to the adult population in acid ponds. It is not possible to predict from the present data what effects these results of acidification may have on regional population because the acid tolerance of embryos varies widely within regions.

The effects of eight trace metals in acid soft water on survival, mineral uptake and skeletal calcium deposition in yolk‐sac fry of brown trout, Salmo trutta L.

Recently hatched fry of brown trout were exposed to each of eight trace metals (Al, Cd, Cu, Fe, Mn, Ni, Pb, Zn) and to a mixture of all eight, at concentrations typical of soft acid waters, in flowing artificial soft water medium at pH 4·5 and 6·5, for 30 days. At pH 4·5, in the absence of trace metals, net uptake of Ca, Na and K and skeletal calcification were impaired but mortalities were low (10%). At pH 4·5, in the presence of Al, Cu, Pb and Zn individually and the mixture, mortalities were high (87–100%). Cd, Fe, Mn and Ni at pH 4·5 each caused some mortalities (17–43%) and impaired skeletal calcification. At pH 6·5, each of Al, Cd, Cu, Fe, Mn, Pb and the mixture of metals impaired net Ca uptake and (except Al, Fe and Pb) skeletal calcification. Net K uptake was impaired by Al and by the mixture, and less severely by Cu and by Fe. Net Na uptake was impaired by Al and by the mixture, and less severely by Fe and by Mn. The role of trace metals other than Al in fisheries’decline in soft acid waters is discussed.

Surface absorption of aluminium by gill tissue and body mucus of rainbow trout, Salmo gairdneri, at the onset of episodic exposure

Rainbow trout were exposed to an episode of artificial soft water at pH 5.4 containing 0.95 mg 1 ‐1 of aluminium for 1 h and gill, skin, body mucus and blood aluminium concentrations were determined. Skin and blood showed no significant increase in aluminium content, whereas whole gill tissue and body mucus showed significant increases. The results are discussed in terms of the gill and body mucus being major sites of aluminium absorption, and a tentative mechanism for aluminium absorption is discussed.

A Kinetic Method for the Measurement of Zinc Influx in vivo in the Rainbow Trout, and the Effects of Waterborne Calcium on Flux Rates

ABSTRACT Three methods were evaluated to measure rate of influx of Zn into rainbow trout. The first two, disappearance of 65Zn from the water and whole-body counting, overestimated influx when compared with a third method which used a terminal plasma sample to calculate influx. The cause of the overestimate was a short-term adsorption phenomenon to both the experimental apparatus and the exterior of the fish. The third method measured only Zn which entered the fish. This method entailed ‘calibration’ of cannulated trout by constant infusion of small amounts of radiolabelled Zn. This was analogous to the entry of Zn into fish across the gill. After 24-36 h of infusion, plasma radioactivity reached a steadystate concentration which was a simple linear function of the rate of infusion. This relationship was then used to predict influx from a single terminal plasma sample from uncannulated trout exposed to radiolabelled Zn in the water. Trout acclimated to tapwater (Ca2+= 2·0 mequiv P1) and exposed to Zn (1·5–45·9 /μequiv I−1; 0·05–1·5 mg I−1) showed saturable uptake which was apparently first order with no significant linear component. The apparent Jmax and Km were 314nequivkg−1 h−1 and 7·3iμequivl_1 (0·24mgl−1), respectively. Acutely raising the waterborne [Ca2+] (4·7 and 9·7 mequiv I−1) over the same range of [Zn] revealed a competitive type of interaction -little change in Jmax, with increased Km. When Ca2+ was acutely removed (0-05 and 1-02 mequiv I−1) by the use of artificial soft water, significant linear influx occurred in addition to the saturable uptake noted at higher [Ca2+], suggesting the opening of a paracellular leak. Calculation of the inhibitor constant for Ca2+ yielded a value of 0·48 mequiv I−1. This value is similar to the Km for Ca2+ when it was a transported substrate (0·28 ± 0·07 mequiv I−1). The true Km for Zn transport in the absence of Ca2+ was 1-Oqequivl−1 (0·06mgl−1). These data showed Zn influx to be saturable and strongly dependent upon waterborne [Ca2+], perhaps traversing the gill in a manner similar to Ca2+.

Zinc Influx Across the Isolated, Perfused Head Preparation of the Rainbow Trout (Salmo gairdneri) in Hard and Soft Water

At a waterborne [Zn] of 1.9 mg∙L−1in hard water (~1 mmol Ca∙L−1), Zn influx across an isolated, saline-perfused head preparation of rainbow trout (Salmo gairdneri) was about 1.5 nmol∙kg−1∙h−1through the lamellar pathway and about 1 nmol∙kg−1∙h−1through the filamental route. Flux rates came rapidly to steady state in both pathways. Trout preexposed to artificial soft water (~0.05 mmol Ca∙L−1) for 5 d showed differential stimulation of flux rates to about 42 and 5 nmol Zn∙kg−1∙h−1through the lamellar and filamental pathways, respectively. Under these conditions, steady-state fluxes across the lamellae did not occur until 15–20 min after the start of perfusion. Preparations from hardwater-acclimated trout tested in soft water gave typical hardwater fluxes showing that these changes in influx were not simply due to acute exposure of the gill surface to low waterborne [Ca]. Influxes in softwater trout, studied over [Zn] from 0.4 to 7.5 mg Zn∙L−1, revealed a saturable, first-order uptake with apparent Jmaxand Kmof 150 nequiv∙kg−1∙h−1and 1.5 mg Zn∙L−1(23 μmol∙L−1), respectively. Because the apparent Kmis in the toxic range, Zn is clearly not the primary substrate. Scanning electron micrography revealed hypertrophy and increased apical exposure of chloride cells; this stimulation, coupled with the increase in Zn influx, suggests that chloride cells may be the site of entry of Zn across the gill.

Respiratory stress in rainbow trout dying from aluminium exposure in soft, acid water, with or without added sodium chloride

Rainbow trout exposed to 32 μM aluminium at pH=5.0 in artificial soft water ([Ca(++)]=50 μM), with or without added sodium chloride (150 mM), suffer from severe respiratory stress characterized by hyperventilation, low PaO 2, high PaCO 2, low pHa and high blood lactate concentrations at death. Plasma chloride concentration at death had decreased in the group with no added NaCl, but not in the presence of added NaCl. Median survival times were not significantly different in the two groups. These findings suggest that death under the given conditions is primarily due to impeded gas exchange.

Do Rainbow Trout (Salmo gairdneri) Acclimate to Low pH?

Adult rainbow trout (Salmo gairdneri) previously exposed to long-term sublethal acid stress (3 mo, pH 4.8) in artificial soft water (Ca2+ = 50, Na+ = 50, Cl− = 100 μeq∙L−1) were challenged with acute severe acid exposure (4.5–5 h, pH 4.0). Their response in terms of whole-body ionic exchanges and blood chemistry was compared with that of trout that had no previous history of acid exposure (naive fish). Acute pH 4.0 exposure caused significant ionoregulatory disturbances in both acid-preexposed and naive fish. Rates of net Na+ and Cl− body losses were twice as large in acid-preexposed fish as in naive fish. The two groups showed similar slight net uptake of acidic equivalents. However, the dynamics of acid–base exchange differed, especially with regard to ammonia excretion which was elevated in acid-preexposed fish and inhibited in naive fish. A larger decrease in plasma Na+, red blood cell swelling, and the maintenance of high-stress indicators (elevated plasma glucose and ammonia excretion, depressed osmolality) confirmed that osmo-ionoregulatory disturbances were more intense in acid-preexposed fish than in naive fish. Thus, long-term sublethal acid exposure did not improve but rather significantly decreased the ability of rainbow trout to respond to more severe acid stress. We conclude that acclimation to acid stress does not occur in rainbow trout.