Acute acid exposure of rainbow trout, Salmo gairdneri Richardson: Effects of aluminium and calcium on ion balance and haematology

Rainbow trout, acclimated to low environmental calcium (38 μEq/1) were acutely exposed to either acid water (pH 4.1) or acid water with aluminium (350 μg/1) for 3.5 h. The exposure to Al in acid water provoked a massive whole body ion loss of sodium, chloride and potassium which was twice as high as in fish exposed to acid water. It is demonstrated that the branchial ion loss increased, while the urinary ion loss remained the same in acid + Al conditions compared to control conditions. The presence of higher ambient Ca-levels (190 μEq/1) had no moderating effect on the toxicity of Al to the ion balance. Plasma ion levels and plasma osmolality declined in Al-exposed fish, indicating a possible disturbance of the osmotic equilibrium between the intracellular and extracellular compartments. This phenomenon could also give rise to a swelling of the red blood cells, thus explaining the observed higher haematocrit value in Al-exposed trout.