1989, Dietrich, Daniel R., Schlatter, Christian, Blau, Nenad, Fischer, M.

The comparison of a fish stocking experiment in a Swiss mountain lake (Lake Laiozza) with results obtained in a South Norwegian lake (Lake Liervatn) revealed contradictory results as to the toxicity of the respective acid water. This, even though the pH, aluminium concentration, conductivity, and ionic composition of the two lakes proved to be almost identical. Lake Liervatn water was less toxic and had a substantially higher NaCI concentration. In order to answer the question whether NaCI could have a mitigating effect on pH-aluminium toxicity to fish, experiments were performed in the laboratory using "Synthetic Laiozza", a media made up from deionized water and salts added according to the concentrations found in Lake Laiozza. Synthetic Laiozza was then enriched with 0, 0.125, 0.25, 0.5, and 4.0 meq NaCI per liter media.
The addition of 0, 0.125, 0.25 and 0.5 meq NaCI/L had no significant effect on the survival time of the fish (all MT50'S laying between 16 and 23 hours), whereas the addition of 4.0 meq NaCI/L resulted in longer survival of the fish i.e. MT50 = 85 hours. The analyses of plasma electrolytes on the other hand, revealed a progressive reduction in electrolyte loss with increasing ambient NaCI concentration.

1989, Dietrich, Daniel R., Schlatter, Christian

Several attempts to stock fish in acidified alpine lakes have so far proven unsuccessful. In an effort to investigate the problems associated with the stocking of fish, the Swiss alpine Lake Laiozza was chosen for experimentation. An analysis of Lake Laiozza water revealed low ion concentrations (0.5 mg Ca/L, 0.13 mg Na/L, 0.02 mg Cl/L), moderate aluminium concentrations (121 ± 28 µg Al/L), and a moderately low pH (5.41 ± 0.21). As in common practice, one and two year old brown trout were exposed in a closed keep-net in Lake Laiozza. The water of Lake Laiozza proved to be acutely toxic to the fish. Mucous clogging of the gills, gill epithelial damage, plasma electrolyte losses, and high hematocrits were the predominant symptoms observed. All symptoms observed are typical for an acute intoxication with aluminium. This stands in contrast to the generally accepted view that aluminium concentrations lower than 200 µg Al/L should not be toxic to brown trout at a pH 5.4. The low Na and Cl and low Ca concentrations in the Lake Laiozza water seem to have rendered the fish much more susceptible to aluminium intoxication.

1989, Dietrich, Daniel R., Schlatter, Christian

An acute toxicity study of aluminium at low pH, using one-year-old rainbow trout (Salmo gairdneri R.), was performed in a closed recirculating system at pH 5.2, 5.4, and 5.6 with nominal concentrations of 0, 100, 200, and 400 μg A1/l. Mortality (96 h) was dependent on the pH and aluminium concentration. Measurements of aluminium in the plasma of exposed fish, by electrothermal atomic absorption spectrometry (ETAAS), showed a dose-dependent uptake of aluminium, but no correlation of plasma aluminium concentration to the mortality observed. Three major mechanisms of pH-Al toxicity seemed to prevail:
i. Relatively low nominal aluminium concentrations (100 and 200 μg/l) at pH 5.2 as well as 200 μg A1/l at pH 5.4 led to electrolyte loss possibly due to an interaction of aluminium with enzymes and epithelial tight junctions in the gill of the exposed fish.
ii. Exposing fish to Al concentrations ≥100 μg/l and pH values ≥5.2 enhanced cell necrosis, proliferations, and fusions of the secondary lamellae in the gills resulting in the obstruction of the interlamellar space and thus most likely in the impairment of gas exchange. Aluminium fractionation suggested that inorganic monomeric Al was responsible for this tissue damage.
iii. High aluminium concentrations (≥200 μg/l) at moderately low pH (≥5.4) led to clogging of the gills with mucus and thus to an impairment of gas exchange. This mucification was thought to stem from the physical irritation of the gills by accumulating polymeric Al.