Effects of repeated short episodes of environmental acidification on Atlantic salmon (Salmo salar) from a landlocked population.

Chronic or repeated exposure to environmental contaminants may result in allostatic overload, a physiological situation in which the costs of coping affect long-term survival and reproductive output. Continuous measurements in Otra, the largest river in southern Norway, show the occurrence of repeated 24-48 h episodes of acidification. This work investigates the impact of repeated short acidification episodes on a unique land-locked population of normally anadromous Atlantic salmon ("Bleke"). This was done by recording physiological measures of stress and allostatic load in fish exposed for 7 days to continuous or repeated episodes of simulated environmental acidification or untreated Otra water (controls). A standardized acute stress test was performed after these different exposure regimes, with brain and blood samples taken before (baseline) or after the stress test. Treatment effects on stress coping ability were assessed by neuroendocrine indicators, including telencephalic serotonergic activity and plasma cortisol. Continuous exposure to acidification resulted in increased baseline plasma Cl- and Na+ and elevated baseline plasma cortisol compared to episodic exposed fish. However, both episodic and continuous acidification resulted in similar increase in gill Al, indicating similar impact on gill permeability of these two exposures. This suggests a lower impact on the electrolyte homeostasis in episodic compared to continuous exposure and that this effect is not directly related to the effects of Al complexes binding to the gills. Furthermore, there were no treatment induced differences on stress coping ability, suggesting that episodic exposure to the sublethal concentrations of Al in pH 5.5 in the present study do not result in higher allostatic load than in control or continuous exposed Bleke.

Assaying waterborne psychoactive drugs by the response to naturalistic predator cues in the stickleback (Gasterosteus aculeatus).

Ecotoxicological effects of psychiatric drugs and drug metabolites released by the human population are of increasing environmental concern. In this study we evaluate behavioral responses to visual predator cues in wild caught three-spined stickleback (Gasterosteus aculeatus) after exposure to water-born citalopram, a widely prescribed selective serotonin reuptake inhibitor with antidepressant and anxiolytic effects. Fish were exposed to ecological relevant concentrations of citalopram (0.15 or 1.5 µg L-1) for 10 or 20 days. After drug exposure, individual fish were moved to a test arena where they were exposed to two naturalistic visual predator cues; a shadow from beneath, which simulated an approaching fish, and an overhead silhouette of a passing gull. Both visual cues resulted in decreased locomotor activity after post cue presentation. Notably, citalopram exposure resulted in a dose dependent suppression in response to the overhead stimulus. These results show that an ecologically relevant stimulus elicits a robust avoidance behavioral in wild caught fish after 25 min of acclimatization in the test arena. This suggests that the gull stimulus can be utilized as a behavioral endpoint in high flow through assays of ecotoxicological effects of psychiatric drugs and drug metabolites. Furthermore, the short acclimation time of wild caught fish in the test arena, opens for behavioral screening by fish living or kept in water bodies which are potentially impacted by psychiatric drugs.

Neuroendocrine indicators of allostatic load reveal the impact of environmental acidification in fish.

When mobilized from surrounding soils and binding to gills at moderately low pH, aluminum (Al) cations can adversely affect fish populations. Furthermore, acidification may lead to allostatic overload, a situation in which the costs of coping with chronic stress affects long-term survival and reproductive output and, ultimately, ecosystem health. The brain's serotonergic system plays a key role in neuroendocrine stress responses and allostatic processes. Here, we explored whether sublethal effects of Al in acidified water affects serotonergic neurochemistry and stress coping ability in a unique land-locked salmon population from Lake Bygelandsfjorden, in southern Norway. Fish were exposed to untreated water with pH 6.5 and 74 µg Al l-1 or acidified (pH 5.5) water with different aluminum concentrations ([Al]; 74-148 µg l-1) for 5-6 days. Afterward, effects on stress coping ability were investigated by analyzing plasma cortisol levels and telencephalic serotonergic neurochemistry before and after a standardized acute stress test. Before the stress test, positive dose-response relationships existed between [Al], serotonergic turnover rate and plasma cortisol. However, in acutely stressed fish, exposure to the highest [Al] resulted in reduced cortisol values compared with those exposed to lower concentrations, while the positive dose-response relationship between Al concentrations and serotonergic turnover rate persisted in baseline conditions. This suggests that fish exposed to the highest Al concentration were unable to mount a proper cortisol response to further acute stress, demonstrating that neuroendocrine indicators of allostatic load can be used to reveal sublethal effects of water acidification-and potentially, the environmental impacts of other factors.

Transformation of iron species in mixing zones and accumulation on fish gills.

The speciation of iron (Fe) strongly influences the deposition and accumulation on gills causing toxicitytoward fish. The impacts of ferric (Fe(III)) and ferrous (Fe(II)) species on gill accumulation were studied in parallel flow-through channel experiments where Atlantic salmon (Salmo salar L.) was kept in cages. Downstream of the pH 6.3 mixing point, where Fe(III) ions or Fe(ll) ions were added continuously to lake water, the molecular mass of Fe(III) increased within 0.5 min after mixing due to hydrolysis and polymerization, while the Fe(II) species remained as low molecular mass (LMM) species 20 min after mixing. For fish exposed to the Fe(lll) enriched water (0.5 mg L(-1)) the Fe accumulation on gills was high and decreased downstream, while low when Fe(II) was added to water. By adjusting the Fe(II) enriched water to pH 6.7, the oxidation of Fe(II) forming Fe(III) accelerated, the Fe accumulation on fish gills increased by a factor of 3, and high mortality (33%) was observed. Thus, input of Fe(ll) ions, oxidation of Fe(ll) at rates higher than 1.5 microg L(-1) min(-1), and continuous formation of LMM Fe(III) species accumulating on gills can induce toxicity toward fish present in circumneutral freshwaters a long distance downstream from the entry points.

Sodium silicate as alternative to liming-reduced aluminium toxicity for Atlantic salmon (Salmo salar L.) in unstable mixing zones.

When acid aluminium (Al) rich water is limed, unstable mixing zones are formed until equilibrium is reached. In such mixing zones transient high molecular mass positively charged Al-species (HMM Al(i)) being extremely gill reactive are produced, causing toxic effects in fish. The transient HMM Al(i)-species are formed due to hydrolysis and polymerization of low molecular positively charged Al-species (LMM Al(i)), e.g. initiated by liming and the subsequent increase in pH. To counteract the toxicity of transient Al polymers in such mixing zones, sodium silicate, forming non-toxic hydroxyaluminosilicate (HAS) complexes, can be used as alternative to liming. In the present work the effect of sodium silicate on polymerization of LMM Al(i) in unstable mixing zones and subsequent gill reactivity and mortality of fish was compared to results obtained from liming. Diluted sodium silicate (<1.5 g l(-1)) and lime slurry (Ca(OH)(2)), respectively, were continually added to acidified Al-rich water in six different channel-tank systems, to obtain mixing zones with pH 5.9, 6.0 and 6.4, respectively. Utilising in situ size and charge fractionation techniques and following the exposure of Atlantic presmolt (Salmo salar L.) kept in cages at defined stations along the channel-tank systems, changes of Al-species in the mixing zones, the gill reactivity of Al-species and thus Al toxicity could be followed downstream the confluences (time of reaction after mixing: 1-100 min). By increasing the pH of the acid water to 6.0 or 6.4 by sodium silicate, the detoxification of Al was faster than using lime. Using sodium silicate, the transformation of LMM Al(i), the formation of HMM Al(i), the Al deposition in fish gills and fish mortality were lower than using lime. The formation of neutral LMM Al-species (Al(o)) was, however, higher and the formation of colloidal Al-species (Al(c)) lower in the presence of silicate compared to lime. Furthermore, the Al deposition in fish gills and fish mortality decreased by increasing concentration of sodium silicate dosed. Thus, sodium silicate is a good alternative to liming, and under certain circumstances when aging of water may represent a problem (e.g. aquaculture) sodium silicate should be the preferred agent.