Episodic exposure to acid and aluminium in soft water: survival and recovery of brown trout,<i>Salmo trutta</i> L.

Abstract

Yolk‐sac fry, swim‐up fry and 1–2 yr juveniles of brown trout, Sulmo trutta L., were exposed to episodes of aluminium and low pH, maximum aluminium concentration 12 μmol l −1 (323 μg l −1 ), minimum pH 4.5, total duration up to 54 h (yolk‐sac fry) or up to 78 h (swim‐up fry and juveniles), in an artificial soft water medium, [Ca] 20 μmol l −1 (0–8 mg l −1 ) (nominal baseline: pH 5.6, zero aluminium concentration). Yolk‐sac fry mortality was nil or very low. A marked increase in susceptibility, with high mortalities, occurred when the yolk was fully absorbed. Mortality of juveniles exposed to two successive episodes was lower than would have been expected on the basis of comparisons with mortalities in single episodes, and mortality declined as the interval between the two episodes was increased. Disturbance of sodium, potassium or calcium balance or gill damage in surviving yolk‐sac fry or juveniles was still evident 5 to 6 days after the end of a single episode.