Effect of aluminium and calcium ions on survival and physiology of rainbow trout Salmo gairdneri (Richardson) eggs and larvae exposed to acid stress

Abstract

Survival and different physiological parameters of developing rainbow trout were investigated during exposure to conditions of low pH, different calcium and aluminium ion levels. In fertilized non-hatched eggs from rainbow trout exposed to different low pH levels mortality occurred at regular intervals during development. Hatching rate was delayed at the lowest ambient pH levels and hatching success was reduced accordingly. The lethal concentration of aluminium ions (LC 50) was 3.8 mg Al/l in soft water and 71 mg Al/l in hard water, when determined on day 25 after hatching at pH 7. In general, exposure to aluminium reduced survival. However, the greatest reduction in survival was observed in relation to the calcium ion concentration of the ambient medium. Exposure to Al reduced dry weight by 9% and respiration rate by 13% in soft water at pH 5. Aluminium ions had only minor effects on the body concentration of Ca and on the cardiac rate. Respiration rate was reduced by 41% by a lowering of pH only, and low pH also had the greatest reducing effect on cardiac rate (32% at pH 5 in soft water). Previous exposure to low pH, low calcium and high aluminium ion concentrations had no significant effect on larval growth after transfer to hard water at pH 7.