Quantitative changes in potassium,sodium, and calcium in the submaxillary salivary gland and blood serum of rats exposed to 2880-MHz microwave radiation

Na⁺, K⁺, and Ca²⁺ concentrations in the blood serum and submaxillary salivary gland (SSG) were investigated in adult, male rats exposed to 2880-MHz microwaves modulated with 1.5-μs pulses at a pulse repetition rate of 1000 Hz or in a hyperthermal environment. Rats were exposed, one at a time, for 30 min to microwaves producing a specific absorption rate (SAR) of: 4.2, 6.3,6.8,8.4, 10.8, or 12.6 W/kg, or were sham exposed under similar environmental conditions. In a second series, one group of rats was exposed singly for 15, 30, or 60 min to microwaves producing an SAR of 9.5 W/kg and other rats were exposed for similar periods at 40 °C; and 10 rats were sham exposed. Flame photometric analysis indicated that the thresholds of microwave radiation required to induce a change in Na⁺, K⁺, and Ca²⁺ concentrations in the salivary glands are 6.8, 6.8, and 6.3 W/kg, respectively. The directions of Na⁺, K⁺, and Ca²⁺ ion shifts in exposed rats' salivary glands are similar, whether affected by microwaves or hyperthermia. Greater changes in Na⁺ and K⁺ concentrations in SSG of rats exposed to microwaves for 15 and 30 min were found than in those exposed at 40 °C. On the other hand, exposure to hyperthermia at 40 °C or to microwaves for 1 h caused Na⁺ concentration to be increased by 68.7 and 59.5% and K⁺ concentration to be decreased by 29.6 and 21.7%, respectively.     

APPLIED ISSUES The effect of ammonium nitrate on the feeding and development of larvae of the smooth newt, Triturus vulgaris (L.), and on the behaviour of its food source, Daphnia

1. Larvae of the smooth newt, Triturus vulgaris, were exposed to four concentrations of ammonium nitrate in artificial pond water (50, 100, 200 and 500 mg 1-^?1) under controlled laboratory conditions. 2. Larvae exposed to a 50 mg 1-^?1 solution of ammonium nitrate showed no significant difference to control larvae in feeding rate, mass at metamorphosis or time to metamorphosis. However, larvae exposed to 200 or 500 mg 1-^?1 ammonium nitrate, for a single period of 24, 48 or 72 h, were significantly smaller than controls at metamorphosis. Larvae exposed to 100 mg 1-^?1 had a significantly higher feeding rate than those reared under control conditions or those exposed to 200 or 500 mg 1-^?1 ammonium nitrate, but this was not reflected in their size at metamorphosis, which was not significantly different from the controls. Larval survival remained high in all trials. 3. In separate trials, Daphnia, used as a food source for the newt larvae, were exposed to the same series of ammonium nitrate concentrations. Daphnia behaviour was affected by exposure to 200 and 500 mg 1-^?1 ammonium nitrate, and in both cases animals were significantly more likely to be found at the top of the water column than those exposed to 50 or 100 mg 1-^?1 ammonium nitrate or the control medium.     

Effect of different salinity on serum osmolality,ion levels and hematological parameters of East Java strain tilapia Oreochromis niloticus

This study evaluated the effect of different salinity levels on the physiology of East Java strain tilapia (Oreochromis niloticus) by measuring the serum osmolalities (SO), ion levels and hematological parameters. Their SOs above the external medium (hyper-osmotic) at 0 and 5 ppt, becoming iso-osmotic at 10 ppt and hypo-osmotic at 15 ppt. The concentrations of serum Na⁺, K⁺, Cl^? and Ca²⁺ in fish acclimated in 0 and 5 ppt were not significantly different. The levels of Na⁺, Cl^– and Ca²⁺ in fish exposed to 10 and 15 ppt were higher than those in fish acclimated at 0 and 5 ppt. In contrast, the levels of K⁺ in fish exposed to 10 and 15 ppt were lower than those in fish exposed to 0 and 5 ppt. The levels of red blood cell, hematocrit and hemoglobin of fish exposed to salinity of 0, 5, 10 and 15 ppt were not significantly different. The levels of white blood cell increased significantly at fish exposed to 10 and 15 ppt. These data provide useful information for future reference and farming practice.     

Evaluation of acute corneal damage induced by 222-nm and 254-nm ultraviolet light in Sprague–Dawley rats

Two hundred twenty-two nanometres ultraviolet (UV) light produced by a krypton–chlorine excimer lamp is harmful to bacterial cells but not skin. However, the effects of 222-nm UV light exposure to the eye are not fully known. We evaluated acute corneal damage induced by 222- and 254-nm UV light in albino rats. Under deep anaesthesia, 6-week-old Sprague–Dawley albino rats were exposed to UV light. The exposure levels of corneal radiation were 30, 150, and 600?mJ/cm². Epithelial defects were detected by staining with fluorescein. Superficial punctate keratitis developed in corneas exposed to more than 150?mJ/cm² of UV light, and erosion was observed in corneas exposed to 600?mJ/cm² of UV light. Haematoxylin and eosin staining also showed corneal epithelial defects in eyes exposed to 254-nm UV light. However, no damage developed in corneas exposed to 222-nm UV light. Cyclobutane pyrimidine dimer-positive cells were observed only in normal corneas and those exposed to 254-nm UV light. Although some epithelial cells were stained weakly in normal corneas, squamous epithelial cells were stained moderately, and the epithelial layer that was detached from the cornea exposed to 600?mJ/cm² of light was stained intensely in corneas exposed to 254-nm UV light. In the current study, no corneal damage was induced by 222-nm UV light, which suggested that 222-nm UV light may not harm rat eyes within the energy range and may be useful for sterilising or preventing infection in the future.     

Effect of exposure to cadmium on the tropical freshwater prawn Macrobrachium rosenbergii

The effect of cadmium (Cd) on mortality, resistance and bioaccumulation in the tropical freshwater prawn Macrobrachium rosenbergii from Egypt were studied. Survival of prawns exposed to Cd doses over 60 μg l^?1 were significantly lower than that of prawns exposed to lower doses. After 96 h prawns exposed to >40 μg l^?1 of Cd had a greater reduction in total haemocyte count and phagocytic activity than those exposed to lower concentrations. Bioaccumulation of Cd in the gills, hepatopancreas and muscles was variable. Cadmium accumulated significantly in the gills and hepatopancreas, but Cd accumulation in the muscles increased only marginally. Macrobrachium rosenbergii manifested histopathological alterations in the gills, hepatopancreas and muscles when exposed to various concentrations of cadmium.     

Peptide heterogeneity in the band 3 protein of rabbit erythrocyte plasma membranes

We have examined the band 3 protein(s) of rabbit erythrocyte membranes by a combination of differential extraction and surface labeling methods. Only one major peptide was labeled when intact red cells were exposed to ¹²⁵I^? and lactoperoxidase; this coincided with band 3. When intact cells were exposed to galactose oxidase followed by [³H]borohydride, numerous surface glycoproteins were labeled, one of which clearly coincided with band 3. Differential extraction with lithium diiodosalicylate revealed one major band 3 glycoprotein which contained both the ¹²⁵I^? and ³H surface labels and three peptides which were unlabeled; these three peptides are apparently not exposed at the cell surface.     

Effects of homogeneous and inhomogeneous static magnetic fields combined with gamma radiation on DNA and DNA repair

The aim of this study was to reveal whether static magnetic fields (SMFs) influence the repair of radiation‐damaged DNA on leukocytes or has any effect on DNA. After 4 Gy of ⁶⁰Co‐γ irradiation, some of the samples were exposed to inhomogeneous SMFs with a lateral magnetic flux density gradient of 47.7, 1.2, or 0.3 T/m by 10 mm lateral periodicity, while other samples were exposed to homogeneous SMF of 159.2 ± 13.4 mT magnetic flux density for a time period of 0.5 min, 1, 2, 4, 6, 18, 20, or 24 h. Another set of samples was exposed to the aforementioned SMFs before gamma irradiation. The following three groups were examined: (i) exposed to SMF only, (ii) exposed to SMF following irradiation by ⁶⁰Co‐γ, and (iii) exposed to SMF before ⁶⁰Co‐γ irradiation. The analysis of the DNA damage was made by single‐cell gel electrophoresis technique (comet assay). Statistically significant differences were found at 1 h (iSMF), 4 h (hSMF), and 18 h (hSMF) if samples were exposed to only SMF, compared to control. When the SMF exposure followed the ⁶⁰Co‐γ irradiation, statistically significant differences were found at 1 h (iSMF) and 4 h (hSMF). If exposure to SMF preceded ⁶⁰Co‐γ irradiation, no statistically significant difference was found compared to 4 Gy gamma‐irradiated group. Bioelectromagnetics 31:488–494, 2010. © 2010 Wiley‐Liss, Inc.     

Nature of norepinephrine-sensitive Ca-pool in rabbit aortic smooth muscle: Effect of pH

High affinity Ca-binding to rabbit aortic smooth muscle microsomes was reduced at low pH. To investigate the role of this Ca-binding, aortic strips were briefly exposed either to pH 5.1 or 7.3, subsequently incubated in a Ca-free medium at pH 7.3, and then challenged with 1 μM norepinephrine (NE). Tissues pretreated at pH 5.1 gave smaller contractions. Tissues loaded with ⁴⁵Ca when exposed to pH 5.1 showed much larger release of ⁴⁵Ca than those exposed to pH 7.3. Subsequently, all ⁴⁵Ca-loaded tissues were placed at pH 7.3 and the effect of 100 μM NE on ⁴⁵Ca-efflux was examined. Tissues exposed previously to pH 7.3 showed a NE-sensitive ⁴⁵Ca-efflux but those pretreated at pH 5.1 did not. The results are consistent with, but do not prove, the hypothesis that the high affinity pH-sensitive Ca-binding to plasma membranes is a large Ca-pool and that the NE-sensitive Ca-pool is a small component of it.     

Composition and distribution of meiofauna,including nematode genera,in two contrasting Arctic beaches

The meiofauna of two tidal beaches, one exposed and one more sheltered, on Bjornoya (Bear Island) was investigated in summer 2000. Both meiofaunal densities and composition seem to be controlled by physical properties of the sediment, which in turn are controlled by exposure. The moderately and poorly sorted sediments in the sheltered beach were more abundant in terms of meiofaunal densities than the well sorted sediments in the exposed beach (254–481 individuals in 10 cm² vs 7–269 individuals in 10 cm², respectively). In total, seven higher meiofaunal taxa were found. Turbellaria were the numerically dominant taxon in the exposed beach. In the sheltered beach, Turbellaria also dominated, followed by Nematoda and Harpacticoida. The vertical distribution of the meiofauna was in accordance with what has been reported from other intertidal beaches. Nematoda were studied in detail and their densities ranged over 0.7–7.7 individuals in 10 cm² in the exposed beach and 2.7–186.0 individuals in 10 cm² in the sheltered beach. Nematodes were identified to genus level and a total of eight nematode genera were found. Sediment community respiration, measured as oxygen consumption, ranged between 2.3 cm³ O₂ m^–2 h^–1 in the exposed beach and 7.3 cm³ O₂ m^–2 h^–1 in the sheltered beach (respectively, the equivalent of 24 mg and 75 mg of organic carbon metabolised per day). Values from the sheltered site are within the range of results registered in much warmer localities.     

Effects of exposure to electromagnetic field from 915 MHz radiofrequency identification system on circulating blood cells in the healthy adult rat

We investigated whether exposure to the 915 MHz radiofrequency identification (RFID) signal affected circulating blood cells in rats. Sprague–Dawley rats were exposed to RFID at a whole‐body specific absorption rate of 2 W/kg for 8 h per day, 5 days per week, for 2 weeks. Complete blood counts were performed after RFID exposure, and the CD4⁺/CD8⁺ ratio was determined by flow cytometry. The number of red blood cells (RBCs) and the values of hemoglobin, hematocrit, and RBC indices were increased in the RFID‐exposed group compared with those in the cage‐control and sham‐exposed groups (P < 0.05). However, the RBCs and platelet numbers were within normal physiologic response ranges. The number of white blood cells, including lymphocytes, was decreased in RFID‐exposed rats. However, there was no statistically significant difference between the sham‐exposed and RFID‐exposed groups in terms of T‐cell counts or CD4⁺/CD8⁺ ratio (P > 0.05). Although the number of circulating blood cells was significantly altered by RFID exposure at a whole‐body specific absorption rate of 2 W/kg for 2 weeks, these changes do not necessarily indicate that RFID exposure is harmful, as they were within the normal physiological response range. Bioelectromagnetics. 39:68–76, 2018. © 2017 Wiley Periodicals, Inc.     

The effect of dissolved oxygen on the growth of young-of-the-year winter flounder,Pseudopleuronectes americanus

Synopsis The effects of constant and diurnally fluctuating levels of dissolved oxygen on the growth of young-of-the-year winter flounder,Pseudopleuronectes americanus, were examined under controlled laboratory conditions. Fish were exposed for either 10 or 11 weeks to constant levels of 6.7 (high) and 2.2 (low) mg l^–1, and a diurnal fluctuation, ranging from 2.5 to 6.4 mg 0₂l^–1. Growth rates, calculated for both standard length and weight, for fish exposed to low and diurnally fluctuating levels were significantly reduced (p < 0.001) as compared to those for fish exposed to the high level. Growth rates of fish exposed to the high level were over twice those of fish held under low oxygen conditions. Under fluctuating conditions, fish grew at intermediate rates. Following these exposures, all fish were subsequently held at 7.2 mg Oz l^–1 for five weeks. Growth rates increased over two and a half times for fish previously exposed to the low oxygen level and were significantly (p < 0.001) higher than for the other two groups.     

Effects of chronic exposure to cadmium- or lead-enriched environments on ionic currents of identified neurons inLymnaea stagnalis L.

Summary 1. Voltage-activated ionic currents of three identified neurons ofLymnaea stagnalis L. were compared in control snails and in animals having been exposed to a cadmium- or lead-enriched environment for 2 weeks. We determined the presence, amplitude, and changes, if any, in the current-voltage characteristics of calcium and potassium currents in each of the three neurons from each of the three groups of animals. Finally, we have compared the effects of acute administration of Cd²⁺ or Pb²⁺ on neurons from control and chronically exposed animals.2. Chronic exposure to cadmium resulted in a near doubling of the high voltage-activated calcium current.3. No differences were found in the effects of acute application of Cd²⁺ or Pb²⁺ on neurons of pretreated and control animals. Cadmium was a potent blocker of the Ca current in either case, while lead caused only a 20% inhibition of the Ca current in neurons of both control and lead-exposed animals.4. Potassium currents were affected in both Cd²⁺- and Pb²⁺-exposed animals. While the sustained outward current was not influenced noticeably, the fast K current was affected in different ways in different neurons. Some did not show this current in the controls but expressed it in neurons from the exposed animals. Other neurons showed the current in the controls and its depression in exposed animals. Acute application of cadmium did not modulate the K current, but lead enhanced the peak amplitude of the transient K current in neurons of both exposed and control snails.     

Macroinfauna community structure and biochemical composition of sedimentary organic matter along a gradient of wave exposure in sandy beaches (NW Spain)

Six sandy beaches on the North West coast of Spain, exposed to different wave action, were sampled in order to study the macroinfauna community and the biopolymeric fraction (proteins, lipids and carbohydrates) of sedimentary organic matter. According to McLachlan’s rating system (1980), three of them were classified as sheltered and the other three as exposed beaches. Sampling was carried out during August 2004 at three tidal levels: high, medium and low. Macroinfauna community and organic matter concentrations were found to be significantly different when sheltered and exposed beaches were compared. Macroinfauna diversity (H′), abundances and biomass became increasingly enriched along a gradient from exposed to sheltered beaches. Macroinfauna mean abundance was found higher in sheltered (ranked from 1535 ± 358 to 15062 ± 5771 ind m⁻²) than in exposed beaches (from 150 ± 41 to 5518 ± 1986 ind m⁻²). Macroinfauna biomass ranged from 3.2 to 14.7 g m⁻² and species richness from 25 to 27 in sheltered localities; while in exposed beaches, biomass ranged from 0.2 to 2.3 g m⁻² and the number of species from 5 to 14. The biopolymeric carbon concentration (BPC) was significantly higher in sheltered (from 84.7 ± 44.7 to 163.3 ± 34.8) than in exposed (from 30.3 ± 7.5 to 78.7 ± 12.3) beaches. The low hydrodynamic conditions of sheltered beaches favoured the settlement of organic rich fine sediments, being supported by the higher protein to carbohydrate ratio found in the exposed (from 23.5 ± 0.9 to 32.7 ± 4.4), rather than in the sheltered localities (from 6.2 ± 0.7 to 13.6). Mean macroinfauna abundances were higher at medium and low tidal levels in both sheltered and exposed beaches. Crustacea was found to be the main group inhabiting the upper part of both types of beaches, dominating all tidal levels of exposed sandy beaches. Mollusca and Polychaeta groups were dominant in sheltered beaches at the medium and lower levels. There was a significant negative relationship between the BPC and the beach face slope; thus, BPC decreased as the intertidal slope increased. It seems that exposed sandy beaches are mainly physically controlled, whereas hospitable sheltered beaches let other factors, such as biochemical compounds, enrich the benthic fauna scenery. Electronic Supplementary Material  Supplementary material is available in the online version of this article at and is accessible for authorized users Handling editors: K. Martens     

A note on copper bioaccumulation in Mozambique tilapia,Oreochromis mossambicus (Osteichthyes: Cichlidae)

Copper (Cu) is one of the most commonly reported metal pollutants in African water bodies, but there are few studies on African freshwater fish species of copper accumulation and copper toxicity. Adult O. mossambicus were exposed to 0mg l^?1 (control) and 0.75mg l^?1 Cu for 96h and 0 (control), 0.11, 0.29 and 0.47mg l^?1 copper for 64 days. Samples of liver and gills were collected after 96h, and after 1, 32 and 64 days, respectively. There were significant differences in the mean Cu accumulation values in the liver and gills between the control and the Cu-exposed fish after the 96-h exposure. In fish exposed to 0.11 and 0.29mg l^?1 Cu for 64 days there was an increase in copper level in the tissues. In fish exposed to 0.47mg l^?1 Cu the concentration in the gill and liver tissue did not increase between Day 1 and Day 32. At this time, Cu accumulation in the liver was higher than for fish exposed to 0.11 and 0.29mg l^?1 Cu for 64 days. Exposure to approximately 0.47mg l^?1 Cu for more than 32 days induced mortality.     

Application of immobilized tannase from <Emphasis Type="Italic">Aspergillus niger</Emphasis> for the removal of tannin from myrobalan juice

Microbial diversity of soil and water samples collected from pyrochemicals exposed areas of Virdhunagar district (Tamil Nadu, India) was studied. Soil and water samples from cultivable area, waste land and city area of the same region were also studied for a comparative acount. There is a remarkable reduction in total heterotrophic bacterial population (THB) in pyrochemicals exposed soil and water samples (42 × 10⁴ CFU/g and 5.6 × 10⁴ CFU/ml respectively), compared to the THB of cultivable area soil and water samples (98 × 10⁷ CFU/g and 38.6 × 10⁷ CFU/ml). The generic composition the THB of the pyrochemicals exposed samples too exhibited considerable change compared to other samples. Pseudomonas sp. was the predominant one (41.6%) followed by Achromobacter sp. (25%) in pyrochemical exposed soil and Pseudomonas sp. was the predominant one (25%) in pyrochemical exposed water samples followed by Bacillus sp. (25%) and Micrococcus sp. (16.6%). It was observed that Cornybacterium sp. and Micrococcus sp. were absent completely in pyrochemical exposed soil and Achromobacter sp. was missing in the pyrochemical exposed water samples, which were present in the other samples. The outcome of this study clearly demonstrates that pollutants such as chemicals used in pyrotechniques affect the microbial biodiversity and suitable measures have to be taken to control the pollution level and to save biodiversity.     

Chronic Internal Exposure to Low Dose 137Cs Induces Positive Impact on the Stability of Atherosclerotic Plaques by Reducing Inflammation in ApoE-/- Mice

After Chernobyl and Fukushima Daï Chi, two major nuclear accidents, large amounts of radionuclides were released in the environment, mostly caesium 137 (¹³⁷Cs). Populations living in contaminated territories are chronically exposed to radionuclides by ingestion of contaminated food. However, questions still remain regarding the effects of low dose ionizing radiation exposure on the development and progression of cardiovascular diseases. We therefore investigated the effects of a chronic internal exposure to ¹³⁷Cs on atherosclerosis in predisposed ApoE^-/- mice. Mice were exposed daily to 0, 4, 20 or 100 kBq/l ¹³⁷Cs in drinking water, corresponding to range of concentrations found in contaminated territories, for 6 or 9 months. We evaluated plaque size and phenotype, inflammatory profile, and oxidative stress status in different experimental groups. Results did not show any differences in atherosclerosis progression between mice exposed to ¹³⁷Cs and unexposed controls. However, ¹³⁷Cs exposed mice developed more stable plaques with decreased macrophage content, associated with reduced aortic expression of pro-inflammatory factors (CRP, TNFα, MCP-1, IFNγ) and adhesion molecules (ICAM-1, VCAM-1 and E-selectin). Lesions of mice exposed to ¹³⁷Cs were also characterized by enhanced collagen and smooth muscle cell content, concurrent with reduced matrix metalloproteinase MMP8 and MMP13 expression. These results suggest that low dose chronic exposure of ¹³⁷Cs in ApoE^-/- mice enhances atherosclerotic lesion stability by inhibiting pro-inflammatory cytokine and MMP production, resulting in collagen-rich plaques with greater smooth muscle cell and less macrophage content.     

Callose Deposition and Photoassimilate Export in Phaseolus vulgaris Exposed to Excess Cobalt, Nickel, and Zinc

Callose accumulated on sieve plates of phloem of white bean seedlings exposed to excess Co, Ni, or Zn. The callose deposits ranged in thickness and were most pronounced in midribs of unifoliate leaves and their subtending petioles. Lesser callose deposits were found in stems. Although translocation of ¹⁴C was reduced drastically in seedlings exposed to excess metal, no correlation was found between translocated ¹⁴C and the amount of callose in the petioles. It is concluded that the inhibition of phloem translocation in seedlings exposed to excess metal is due to effects other than callose deposition.     

Formaldehyde toxicity is altered by calcium and organic matter

Formaldehyde is one of the shortlist substances permitted for use in aquaculture. Toxicity of formaldehyde and therapeutical success is influenced by water parameters. However, there is a lack of information on the interaction of organic carbon and calcium (Ca²⁺) on the toxicity of formaldehyde. Laboratory experiments were conducted to test the combined effects of Ca²⁺ and natural organic matter (NOM) on formaldehyde toxicity. Zebrafish embryos were exposed to five concentrations of formaldehyde for 144 h. Juveniles exposed to high concentrations died; the embryos exposed to low concentrations were unable to hatch, particularly visible in the groups without NOM. The toxicity‐reducing effects of NOM are not attributable to the presence of Ca²⁺.     

Potassium ion influx measurements on cultured Chinese hamster cells exposed to 60-Hertz electromagnetic fields

Potassium ion influx was measured by monitoring ⁴²KCI uptake by Chinese hamster ovary (CHO) cells grown in suspension culture and exposed in the culture medium to 60–Hz electromagnetic fields up to 2.85 V/m. In the presence of the field CHO cells exhibited two components of uptake, the same as previously observed for those grown under normal conditions; both these components of influx were decreased when compared to sham-exposed cells. Although decreases were consistently observed in exposed cells when plotted as log_c of uptake, the differences between the means of the calculated fluxes of exposed and sham-exposed cells were quite small (on the order of 4–7%). When standard deviations were calculated, there was no significant difference between these means; however, when time-paired uptake data were analyzed, the differences were found to be statistically significant. Cells exposed only to the magnetic field exhibited similar small decreases in influx rates when compared to sham-exposed cells, suggesting that the reduction in K⁺ uptake could be attributed to the magnetic field. Additionally, intracellular K⁺ levels were measured over a prolonged exposure period (96 h), and no apparent differences in intracellular K⁺ levels were observed between field-exposed and shamexposed cultures. These results indicate that high-strength electric fields have a small effect on the rate of transport of potassium ions but no effect on long-term maintenance of intracellular K⁺.     

The effects of the cyanobacterium Microcystis aeruginosa, the cyanobacterial hepatotoxin microcystin–LR, and ammonia on growth rate and ionic regulation of brown trout

Brown trout were exposed for 63 days to five treatments: a control; the purified cyanobacterial hepatotoxin microcystin—LR (MC—LR) (41—57 μg MC—LR 1^?1); lysed toxic Microcystis aeruginosa cells (41–68 μg MC—LR 1^?1 and 288 μg chlorophyll a 1^?1); lysed non—toxic M. aeruginosa cells (non—MC—LR containing and 288 μg chlorophyll a 1^?1); ammonia (65–325 μg NH₃ 1^?1). All treatments produced significantly reduced growth compared to controls (P<0·05, Fisher test). Exposure to ammonia resulted weight loss over the first 7 days followed by weight increase, though at a significantly lower level than in the other treatments. First exposed to lysed toxic M. aeruginosa cells grew less than those exposed to lysed non—toxic cyanobacteria or purified MC—LR. Sodium influx rates after 63 days exposure to purified MC—LR, lysed toxic M. aeruginosa cells, or ammonia showed a significant increase compared to control fish or those exposed to lysed non—toxic M. aeruginosa cells. There were no significant differences in Na⁺ efflux or net Na⁺ uptake rates between treatments. Significant increases in body Na⁺ and Cl^— were seen in fish exposed to lysed toxic M. aeruginosa cells or ammonia. Only fish exposed to ammonia showed a significant increase in body ammonia. Short—term exposure, over 4 h, to lysed toxic cells, non—toxic cells or purified MC—LR resulted in insignificant changes in Na⁺ flux rates compared to controls although there was a significant net Na⁺ loss in fish exposed to ammonia. Chronic exposure of fish to toxic cyanobacterial blooms may result in ionic imbalance and reduced growth.