Frode Kroglund

Increased mortality of fish due to changing Al-chemistry of mixing zones between limed streams and acidic tributaries

The present study is mainly focusing on mortality variations of fish due to changing Alchemistry of mixing zones. An artificial mixing zone was made by pumping water from a limed stream and an acidic tributary into a mixing channel. Atlantic salmon (Salmo salar L.) parr were exposed to the mixed water, limed stream water, and acidic tributary water. Mortality, blood haematocrit and plasma Cl−-concentration were recorded. Neither mortality, nor changes in haematocrit and plasma Cl− were observed when fish were exposed to limed water, while in both acidic and mixed water, mortalities and loss of plasma Cl− were observed. The highest mortality rates were found within the initial part (0 to 20 s) of the mixing zone. Blood haematocrit increased only in fish exposed to acidic tributary water. Our results shows that changes in Al-chemistry and subsequent Al-polymerization occur when acidic tributary water is mixed with limed stream water. We have also demonstrated that the toxicity which can arise in mixing zones are greater than in the original acidic water before mixing. The variations in mortality observed are associated with the quality and quantity of Al-polymerization as well as ageing of the polymers.

Impact of early salmon louse, Lepeophtheirus salmonis, infestation and differences in survival and marine growth of sea‐ranched Atlantic salmon, Salmo salar L., smolts 1997–2009

The impact of salmon lice on the survival of migrating Atlantic salmon smolts was studied by comparing the adult returns of sea-ranched smolts treated for sea lice using emamectin benzoate or substance EX with untreated control groups in the River Dale in western Norway. A total of 143 500 smolts were released in 35 release groups in freshwater from 1997 to 2009 and in the fjord system from 2007 to 2009. The adult recaptures declined gradually with release year and reached minimum levels in 2007. This development corresponded with poor marine growth and increased age at maturity of ranched salmon and in three monitored salmon populations and indicated unfavourable conditions in the Norwegian Sea. The recapture rate of treated smolts was significantly higher than the controls in three of the releases performed: the only release in 1997, one of three in 2002 and the only group released in sea water in 2007. The effect of treating the smolts against salmon lice was smaller than the variability in return rates between release groups, and much smaller that variability between release years, but its overall contribution was still significant (P < 0.05) and equivalent to an odds ratio of the probability of being recaptured of 1.17 in favour of the treated smolts. Control fish also tended to be smaller as grilse (P = 0.057), possibly due to a sublethal effect of salmon lice.

Low concentrations of inorganic monomeric aluminum impair physiological status and marine survival of Atlantic salmon

Two strains of Atlantic salmon (Salmo salar) presmolts were exposed for 3 months to moderately acidic water (pH 5.8; 6±2 μg aluminum (Ali) l−1 inorganic monomeric aluminum-acid exposure group) or non-acid water (pH>6.5–6.9; <5 μg Ali l−1—Good/control group) at NINA Research Station, Ims, Southern Norway. Exposure to low concentrations of Ali raised the gill-aluminum (gill-Al) concentration by 20–30 μg Al g−1 gill dry weight compared to control fish having <10 μg Al g−1 gill dry weight. The fish responded to the Al loading with elevated blood glucose, but retained more normal hematocrit and plasma chloride levels. Fish exposed under acid conditions grew significantly poorer than the control fish. After 3 months of exposure, 150 Carlin-tagged smolts from both Imsa treatments were released into the non-acidic River Imsa, 800 m upstream from a trap that caught all migrating smolts. Acid-exposed fish migrated downstream slightly later than the controls. At the same time, Carlin-tagged fish from all four treatments (Acid and Good, both strains; approximately 1000 fish group−1) were released downstream of the trap located 150 m above the river mouth. Based on the number of adult recaptures (by May 2001), marine survival was 20–30% lower for the acid-exposed fish than for the controls. There were no differences in marine growth between the treatments. The results suggest that even very low concentrations of Ali (6±2 μg l−1) can reduce seawater survival, thereby having effect on the population level. The physiological responses, reduced growth and reduced marine survival also suggest that the presmolts did not acclimate to the acid conditions.

Time and Ph-Dependent Detoxification of Aluminum in Mixing Zones between Acid and Non-Acid Rivers

Liming detoxifies aluminum in a time-dependent process following the increase in pH. Transformation of Ali into non-reactive or colloidal forms of Al reduces toxicity. To investigate the effects of pH on the detoxification rate, Atlantic salmon (Salmo salar) parr were exposed in four identical channel-tank setups differing only in mixing ratio (30:70, 16:84 or 6:94) between acid (pH 5.6, total Ali 90 µg Al·L−1) and non-acid water (pH 6.3, total Ali 3 µg Al·L−1). Two channels had identical mixing ratio (30:70), but differed with respect to pH (6.0 or >6.4) due to addition of lime. Fish were exposed for 140 hrs. in waters aged from 1 minute and up to 4 hours after mixing. Ali decreased within minutes after mixing at pH 6.4. The detoxification process required hours at pH 6.0. Al accumulation onto fish gills and fish homeostasis was related to Ali. The data suggest that the detoxification process, and therefore the water body affected by ongoing polymerization, was strongly influenced by pH, where a pH target for liming set at pH 6.4 detoxified water faster than a pH target of pH 6.0.

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.

Water Quality Dependent Recovery from Aluminum Stress in Atlantic Salmon Smolt

In Norway, a variable pH target (pH 6.2–6.4 during most of the year, but 6.4 during the smoltification period) is used to reduce the cost of liming salmon rivers. Here we test the adequacy of this liming strategy. Atlantic salmon presmolts exposed to sublethal acidic water (pH 5.9, <25 µg Ali·L−1) for more than 3 months showed impaired sewater tolerance, elevated gill-Al concentrations, severe gill tissue changes, elevated blood plasma glucose concentrations, but no effect on blood plasma chloride. It is usually assumed that smolt will recover from prior aluminum (Al) exposure if water quality is restored. Recovery rate is here used as an indirect measure of water quality improvements achieved after treating acid water (pH 5.8, 85 µg Ali·L−1) with lime to reach pH-target levels of 6.0 – 6.3. Fish were exposed in a channel-tank set-up for >210 hrs in water aged from 1 minute up to 2 hours after treatment (in a flow through system). More Al was eliminated from the gills when the fish were exposed to pH 6.3 than to pH 5.8 or 6.0, and when water was aged after pH increase. Recovery, defined as return of normal gill morphology, blood homeostasis and establishment of seawater tolerance was achieved within 210 hrs in channels treated with lime to pH 6.3, while a similar recovery was not obvious at lower pH values. Liming to pH 6.3 detoxified Al better than pH 6.1.

Tolerance to Acid Water Among Strains and Life Stages of Atlantic Salmon (Salmo Salar L.)

Reintroduction of Atlantic salmon (Salmo salar L.) after liming of acidified barren salmon rivers could benefit by choosing acid tolerant strains. Testing different life history stages from fry to smolts of five salmon strains with different acidification history demonstrated strain-specific variation in tolerance to acid aluminum-rich waters for stages from fry to parr. Contrary to expectation, salmon from non-acidified rivers were more tolerant. Differences in sensitivity were found between life history stages. Within a specific life history stage, size-dependent sensitivity was found; small fish being more sensitive to pH while large fish were more sensitive to aluminum. Presmolts showed the same relative tolerance between strains as younger stages. These differences disappeared, however, when the smolt reached full smoltification, probably due to supersensitivity at this stage. Poor water quality during the last period of smoltification and outmigration can thus mask the genetic potential for tolerance to acidic rivers.

Water quality requirement of Atlantic salmon (Salmo salar) in water undergoing acidification or liming in Norway

Atlantic salmon are severely affected by acidification in Norway. Water quality criteria for the salmon have to be based on the most sensitive stage, the smolt stage. The sensitivity to acidic water increases enormously during smolting, the seawater tolerance being especially vulnerable. Even moderately acidic water (pH about 6) with low inorganic monomeric aluminium (LA1) concentrations (<20μg. L−1) and short-term episodes may be harmful. Mixing zones in limed or unlimed rivers may also represent a problem for seaward migrating smolts. In limed salmon rivers, the national liming goal has been increased to pH 6.5 during smolting (1 February to 1 July) and to 6.2 the rest of the year as a result of our experiments. In contrast to what has been found for brown trout, salmon strains originating from watercources undergoing acidification were not more tolerant than those from non-acidic watercourses. At the moment no such “tolerant” strains are available for restocking limed rivers in Norway.

Effects of acidic water and aluminum exposure on gill Na+, K+-ATPase α-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.

Aluminium in acidic river water causes mortality of farmed Atlantic Salmon (Salmo salar L.) in Norwegian fjords

Abstract Acute mortality of Atlantic salmon has been described from fjord-based fish farms in Western Norway. Mortality is often related to snowmelt and heavy rainfall in the catchment areas during the winter. Increased freshwater runoff reduces the surface water salinity from >20 to 200 μg g−1 dry weight). The increases in gill Al were related to increased discharge episodes where acidic, Al-rich freshwater elevated the surface water concentrations of Al from 70 μg Al l−1. Increased mobility of reactive Al (Ala) and increased Al accumulation on gills during flood episodes was the probable cause of the massive salmon mortality.