Migratory passage structures at hydropower plants as potential physiological and behavioural selective agents.

Anthropogenic activities affect fish populations worldwide. River dams have profound impacts on ecosystems by changing habitats and hindering migration. In an effort to counteract such effects, a range of mitigation measures have been installed at hydroelectric power plants. However, not all individuals in a population use these measures, potentially creating strong selection processes at hydroelectric power plants. This may be especially true during migration; fish can get heavily delayed or pass through a hydropower turbine, thus facing increased mortality compared with those using a safe bypass route. In this study, we quantify migration route choices of descending wild passive integrated transponder (PIT)-tagged Atlantic salmon smolts released upstream from a hydroelectric plant. We demonstrate how only a few metres' displacement of bypass canals can have a large impact on the fish guidance efficiency (FGE). The proportion of fish using the bypasses increased from 1% to 34% when water was released in surface gates closer to the turbine intake. During a period of low FGE, we observed two different smolt migratory strategies. While some individuals spent little time in the forebay before migrating through the turbine tunnel, others remained there. We suggest that these groups represent different behavioural types, and that suboptimal mitigation measures at hydropower intakes may, therefore, induce strong selection on salmon behavioural traits. The ultimate outcome of these selection mechanisms is discussed in light of potential trade-offs between turbine migration mortality coast and optimal sea entrance timing survival benefits.

Development and application of a biotic ligand model for predicting the chronic toxicity of dissolved and precipitated aluminum to aquatic organisms.

Aluminum (Al) toxicity to aquatic organisms is strongly affected by water chemistry. Toxicity-modifying factors such as pH, dissolved organic carbon (DOC), hardness, and temperature have a large impact on the bioavailability and toxicity of Al to aquatic organisms. The importance of water chemistry on the bioavailability and toxicity of Al suggests that interactions between Al and chemical constituents in exposures to aquatic organisms can affect the form and reactivity of Al, thereby altering the extent to which it interacts with biological membranes. These types of interactions have previously been observed in the toxicity data for other metals, which have been well described by the biotic ligand model (BLM) framework. In BLM applications to other metals (including cadmium, cobalt, copper, lead, nickel, silver, and zinc), these interactions have focused on dissolved metal. A review of Al toxicity data shows that concentrations of Al that cause toxicity are frequently in excess of solubility limitations. Aluminum solubility is strongly pH dependent, with a solubility minimum near pH 6 and increasing at both lower and higher pH values. For the Al BLM, the mechanistic framework has been extended to consider toxicity resulting from a combination of dissolved and precipitated Al to recognize the solubility limitation. The resulting model can effectively predict toxicity to fish, invertebrates, and algae over a wide range of conditions. Environ Toxicol Chem 2018;37:70-79. © 2017 SETAC.

Atlantic salmon (Salmo salar L.) smolts require more than two weeks to recover from acidic water and aluminium exposure.

The detrimental effects of acid rain and aluminium (Al) on salmonids have been extensively studied, yet knowledge about the extent and rate of potential recovery after exposures to acid and Al episodes is limited. Atlantic salmon smolts in freshwater (FW) were exposed for 2 and 7-day episodes (ACID2 and ACID7, respectively) to low pH (5.7±0.2) and inorganic aluminium (Ali; 40±4 µg) and then transferred to good water quality, control water (CW; pH 6.8±0.1; <14±2 µg Ali). Al accumulation on gills after 2 and 7 days of acid/Al exposure was 35.3±14.1 and 26.6±1.8 µg g(-1) dry weight, respectively. These elevated levels decreased 2 days post transfer to CW and remained higher than in control (CON; 5-10 µg Ali) for two weeks. Plasma Na(+) levels in ACID2 and ACID7 smolts decreased to 141±0.8 and 138.6±1.4mM, respectively, and remained significantly lower than CON levels for two weeks post transfer to CW. Similarly, plasma Cl(-) levels in ACID7 smolts (124.3±2.8mM) were significantly lower than in CON, with Cl(-) levels remaining significantly lower in ACID7 (126.2±4.8 mM) and ACID2 (127.6±3.7 mM) than in CON following 9 and 14 days post-transfer to CW, respectively. ACID2 and ACID7 smolts sustained elevated plasma glucose levels post transfer to CW suggesting elevated stress for more than a week following exposure. While gill Na(+), K(+)-ATPase (NKA) activity was only slightly affected in ACID2 and not in ACID7 smolts in FW, acid/Al exposure resulted in a transient decrease in NKA activity following SW exposure in both groups. Acid/Al episodes had limited impact on isoform specific NKA α-subunit mRNA during exposure. However, the transfer of ACID2 and ACID7 smolts to CW showed an increase in NKAα1a mRNA (the FW isoform) and inhibited the up-regulation of NKAα1b (the SW isoform), probably resulting in higher abundance of the enzyme favouring ion uptake. Gill caspase 3B gene transcription did not change in acid/Al treated smolts, indicating no increased apoptosis in gills. ACID2 and ACID7 treatments resulted in lower smolt-related gill transcription of the gene encoding the tight junction protein claudin 10e compared to CON, while the gene encoding claudin 30 showed lower mRNA expression only after 11 days SW exposure in ACID7 fish. Our data suggest that acid/Al conditions affect ion perturbations through a combination of alteration of the preparatory increase in paracellular permeability and negative impact on the SW type NKA α-subunit mRNA transcripts, and raise major concerns regarding the recovery of physiological disruption in smolts following acid/Al exposure. Smolts may require more than two weeks to fully recover from even short moderate episodes of acid/Al exposure. Acid/Al exposure thus probably has greater impact on salmon populations than previously acknowledged.

Effects of the fungicide azoxystrobin on Atlantic salmon (Salmo salar L.) smolt.

Atlantic salmon smolts were exposed to three doses of the fungicide azoxystrobin for 4 days, and physiological blood parameters and transcriptional effects in liver and muscle were evaluated in search for potential negative effects. Azoxystrobin exposure mediated up-regulation of catalase, MAPK1 and IGFBP1 in liver tissue. Catalase, transferrin, IGFBP1 and TNFR were up-regulated and CYP1A down-regulated in muscle tissue. Blood parameters glucose, hematocrit, pCO(2), HCO(3) and pH grouped together with transcripts levels of MnSOD, MAPK1, IGFBP1, MAP3K7 and GPx4 in liver of fish exposed to the highest azoxystrobin concentration (352 µgL(-1)) using principal component analysis (PCA). In muscle, the blood parameters glucose, hematocrit, pCO(2), HCO(3) and pH grouped together with transcript levels of heme oxygenase, thioredoxin, MnSOD, TNFR and MMP9. These results suggest that the fungicide azoxystrobin affects mitochondrial respiration and mechanisms controlling cell growth and proliferation in fish and may have negative effects on juvenile Atlantic salmon.

Effects of acidic water and aluminum exposure on gill Na(+), K(+)-ATPase alpha-subunit isoforms, enzyme activity, physiology and return rates in Atlantic salmon (Salmo salar L.).

Na(+), K(+)-ATPase (NKA) is involved, through its role as a major driving force for electrochemical gradients, in a range of transmembrane transport processes. Maintenance of homeostasis in anadromous salmonids requires modulation of several gill ion secretory proteins as part of the preparatory adaptation and acclimation to marine life. Atlantic salmon smolts were exposed to combinations of low pH and inorganic aluminum (acid/Al(i)) in freshwater (FW) and were then transferred to seawater (SW) for studies of post-smolt performance. Gill mRNA levels of four NKA-alpha isoforms (alpha1a, alpha1b, alpha1c and alpha3) of the catalytic NKA subunit and NKA enzyme activity were measured. Moderate acid/Al treatment (MOD, pH 5.9+/-0.3, 15+/-9microgl(-1)Al(i)) prevented the FW preparatory increase in NKA activity observed in control (CON, pH 6.9+/-0.1, 8+/-3microgl(-1)Al(i)) smolts, while high acid/Al treatment (SEV, pH 5.6+/-0.2, 30+/-7microgl(-1)Al(i)) caused a rapid and persistent reduction in NKA activity. Correspondingly, a 3.3-fold increase in plasma glucose levels in the SEV groups concurrent with a decrease in plasma chloride levels suggest that acid/Al exposed fish were stressed and experienced problems maintaining ion homeostasis. Gill NKA activities in acid/Al exposed groups were re-established after 28 days in SW. Both long (9 days) and short-term (2.5 days) treatments had significant impact on isoform-specific Na(+), K(+)-ATPase alpha-subunit mRNA abundance in the FW period. Acid/Al exposed groups lacked the preparatory increases in all NKA-alpha isoform mRNA levels seen in the CON group, except for alpha1a. In contrast to the other isoforms measured, alpha1a mRNA abundance decreased sharply upon SW transfer, supporting the hypothesis of isozyme shifting as a mechanism of altering the gill from an ion absorbing to an ion excreting tissue during smoltification and SW exposure. Adult return rates to the Imsa river were significantly reduced both in short-term (78% of controls) and long-term (55% of controls) acid/Al exposures, emphasising the physiological and ecological consequences of acid/Al exposure during smoltification.

Gill reactivity of aluminium-species following liming.

In acidified aluminium (Al) rich freshwater positively charged Al-species (Al(i)) are the key toxic components due to the accumulation in fish gills. As a countermeasure, liming is used to increase the pH and reduce the concentration of Al(i)-species; in particular low molecular mass (LMM) Al(i)-species by hydrolyses. However, very toxic high molecular mass (HMM) Al polymers can form in the unstable mixing zone immediately after liming. In the present work gill reactivity of LMM and HMM Al-species was studied under controlled conditions in eight channel-tank mixing zone systems in the field where Atlantic salmon (Salmo salar L.) kept in cages were exposed to defined mixing zone water. Mixing zones were created by continually liming acid river water (pH 5.0-5.7) high in LMM Al(i) to pH 6.0 and 6.4, respectively. Transformation processes affecting the Al-speciation as a function of time after liming were documented by in situ hollow fibre ultrafiltration interfaced with ion chromatography, while the Al accumulation in fish gills was used as bioindicator. For fish exposed to mixing zone water immediately after liming (1 min) the Al accumulation in gills (mug Al g(-1)) was higher (factor of 2) than for fish exposed to acid water prior to liming, due to the formation of gill reactive HMM Al(i)-species. The Al accumulation in gills followed a first order kinetic expression reaching steady-state conditions after 24-h exposures. The deposition rate of Al in gills (mug Al g(-1) h(-1)) correlated with the water concentrations of HMM Al(i) (R(2)=0.80) in the mixing zones, and for LMM Al(i) in the acid water (R(2)=0.92). Due to the transient nature of HMM Al(i) the deposition rate of Al decreased from the point of liming with a factor of 10 downstream the channel-tank system (i.e. 100 min after liming). The concentration of gill accumulated Al was higher (factor of 3) immediately after high level liming (pH 6.4) than following low level liming (pH 6.0). However, high level liming was more efficient in detoxifying Al in downstream waters. Furthermore, the bioavailability of a given LMM Al(i) concentration as well as bioreactivity following liming was dependent on the TOC and silicon concentration in the acid water. Increased concentration of TOC (1.5 to 4.3 mg l(-1)) and silicon (0.3 to 1.0 mg l(-1)) reduced the gill reactivity of Al(i) by approximately 50%.

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.

Fish mortality during sea salt episodes--catchment liming as a countermeasure.

Aluminium (Al) toxicity is usually associated with acid rain and acidified freshwater systems. The present work demonstrates that acute fish mortality (50%) also occurs in moderate acidified salmon rivers during sea salt episodes. Furthermore, catchment liming was proved to be an efficient measure to counteract the fish toxicity. The impact of sea salt episodes on river water qualities and on Atlantic Salmon (Salmo salar L.) was studied in two rivers situated at the west coast of Norway. During February-May 2002, fish were kept in tanks and continually exposed to the changing water qualities. Changes in Al-species were followed using in situ fractionation techniques. During storm events and high sea salt deposition, the sea salt concentration increased (190 to 580 microM Cl), pH decreased (pH 5.3 to 4.6) and the concentration of low molecular mass (LMM) cationic Al-species (Al(i)) increased (0.7 to 3.0 microM) in the river. Subsequently, Al accumulated in fish gills (6 to 19 micromol g(-1) dw) causing ionoregulatory and respiratory failures as well as mortality. In water the concentration of LMM Al(i) stayed enhanced during four weeks, while the physiological stress responses in surviving fish remained high for a longer time (>eight weeks). To counteract Al toxicity, one of the tributary catchments had been limed four years earlier. Due to catchment liming (1000 kg ha(-1)) the water concentration of LMM Al(i)(<0.7 microM) and the Al accumulation in gills remained relatively low (<7 micromol g(-1) dw) during the storm and no fish mortality occurred.

Diffusive gradients in thin films sampler predicts stress in brown trout (Salmo trutta L.) exposed to aluminum in acid fresh waters.

Increased levels of aluminum ions released from nutrient-poor soils affected by acid rain have been the primary cause of fish deaths in the acidified watersheds of southern Norway. The complex aluminum chemistry in water requires speciation methods to measure the gill-reactive species imposing toxic effects toward fish. Previously, aluminum speciation has mainly followed the fractionation principles outlined by Barnes/Driscoll, and several analogues of these fractionation principles have been used both in situ and in the laboratory. Due to rapid transformation processes, aluminum speciation in water samples may change even during short storage times. Thus, results obtained by laboratory fractionation methods might be misleading for the assessment of potentially toxic aluminum species in the water. Until now, all in situ field fractionation methods have been time and labor consuming. The DGT technique (diffusive gradients in thin films) is a new in situ sampler collecting a fraction of dissolved metal weighted according to the rate of diffusion and dissociation kinetics. In a field experiment with acid surface water we studied the DGT sampler as a new prediction tool for the gill accumulation of aluminum in trout (Salmo trutta L.) and the induced physiological stress responses measured as changes in blood glucose and plasma chloride. Aluminum determined with DGT (DGT-AI) was higher than labile monomeric aluminum (Ali) determined with a laboratory aluminum fractionation procedure (PCV--a pyrocatechol violet analogue of Barnes/Driscoll), a difference due to collection of a fraction of organically complexed aluminum by DGT and a reduction of the Ali fraction during sample storage. DGT-AI predicted the gill uptake and the aluminum-induced physiological stress responses (increased blood glucose and decreased plasma chloride, r2 from 0.6 to 0.9). The results indicate that DGT-AI is a better predictor for the stress response than laboratory-determined Ali, because the DGT sampler collects a more correct fraction of the gill-reactive aluminum species that induces the stress.

Transformation of positively charged aluminium-species in unstable mixing zones following liming.

Liming is widely used to counteract chronic toxicity of positively charged monomeric aluminium species (Ali). Immediately after liming, unstable mixing zones are formed due to the sudden increase in pH. Transformation of monomeric Ali species takes place instantaneously and transient positively charged Al polymers, being acute toxic to fish, are formed in the mixing zones. Using in situ hollow fibre ultrafiltration interfaced with ion chromatography in unstable mixing zone field experiments performed in two river systems situated south and southwest of Norway, information on time-dependent transformations of low molecular mass (LMM) and high molecular mass (HMM) positively charged Ali-species has been followed. The formation of HMM Ali species from LMM Ali occurred rapidly following liming. HMM Ali species have a certain lifetime and are transformed to high molecular mass neutral Al-species (HMM Alo) and then to non-reactive colloidal Al species (HMM Alc). Concentration levels of transient Al-species formed in the mixing zone and the rate of transformation depend on the concentrations of LMM Ali species, Al complexing ligands (DOC and Si) in the input water and on pH in the mixing zone after liming. A dynamic model describing transformation processes influencing the Al speciation in mixing zones following a sudden increase in pH is suggested. Based on the experimental results, associated rate constants and half-lives for transient Al-species were estimated.

Mobilization of aluminium and deposition on fish gills during sea salt episodes--catchment liming as countermeasure.

Episodic events may be critical with respect to aluminium (Al) toxicity in moderately acidified salmon rivers. The present work demonstrates that sea salt episodes enhance the toxicity of Al in acidic rivers. The documented sea salt episode (300 [micro sign]M Cl) mobilized positively charged Al species (0.4 to 1.1 [micro sign]M Al(i)), enhanced the Al accumulation on fish gills (0.9 to 10 [micro sign]mol g(-1) dw) and caused increased stress responses (6 to15 mM blood glucose) in fish. Accumulated Al on gills remained high several days after the episode. The presented results are based on a six-week field study in two tributary rivers on the west coast of Norway. Changes in the river water qualities and Al speciation were followed using in situ fractionation techniques. Al accumulation on gills and stress responses were followed for Atlantic salmon (Salmo salar) kept in tanks continually exposed to the changing water quality. The potential mobilization of Al from the two catchments was studied by extracting soils with diluted seawater (salinity of 3). To counteract Al toxicity, one of the tributary catchments has been limed. The potential mobility of Al by sea salt was lower in limed soils compared to acid soils, and the Al deposition on fish gills (<3.5 [micro sign]mol g(-1) dw) and associated stress responses stayed low during the sea salt episode in the river draining the limed catchment. Thus, for acid river systems in coastal areas, catchment liming should be considered as a useful countermeasure for Al toxicity.