Effects of temperature on the recovery of juvenile grayling (Thymallus thymallus) from exposure to Al + Fe

Abstract

One-summer-old graylings (Thymallus thymallus ) were exposed for 6 days to water containing a mixture of 1 mg l-1 Fe and 100 mg l-1 Al at pH 5.5, with or without 15 mg l-1 humic acid. A pH of 6.9 was used as a control. The experiment was performed at two test temperatures, 13 and 3 8C. After 1 week of exposure, half of the fish in the tank were taken for oxygen measurement and tissue sampling. The remaining half were maintained in metal-free water for a further week to assess their recovery at the two test temperatures. Fifty percent of the fish died under metal exposure at 13 8C, but none at 3 8C. Despite of the lack of mortalities at the lower temperature, surviving fish at both test temperatures suffered similar gill damage (adherence of lamellae), disturbances in ion regulation, increases in haematocrit value (Hct) and haemoglobin (Hb) concentration and reductions in oxygen consumption. The addition of humic acid prevented these changes. The reduced plasma chloride concentration, increased blood Hct value and Hb concentration recovered completely at 13 8C, whereas the lowered oxygen consumption recovered less completely, which may be attributed to the remaining minor gill damage (lamellar hypertrophy). At the lower temperature, the adherence of lamellae persisted after the recovery period, and oxygen consumption, therefore, remained at a very low level. The decreased plasma chloride concentration was also unable to recover. The accumulation of Al inside the gill tissue was greater at low temperature. We conclude that the acute toxicity of a mixture of Fe and Al to grayling and their subsequent ability to recovery is dependent on the exposure temperature.