The effects of Fe and Al exposure with or without humic acid at two pH levels on the gills, oxygen consumption and blood and plasma parameters of juvenile grayling (Thymallus thymallus).

Abstract

One-summer-old grayling (Thymallus thymallus) were exposed to combinations of low pH (5 and 6), iron (0 and 2 mg l -1 ), aluminium (0 and 200 μg l -1 ) and humic acid (0 and 15 mg l -1 ) for three days. Gill damage was evident when metals were added to the water, which resulted in greatly reduced oxygen consumption, but humic acid protected the gills. Exposure to Al and Fe caused considerable mortality at pH 5, whereas only one fish died at pH 6. Nevertheless, Al and Fe individually and in combination were toxic at pH 6 as indicated by haematological changes, a reduced plasma chloride concentration and a high blood glucose concentration. These responses correlated with the accumulation of metals in the gills. Apart from increased mucus production at pH 5 + Al, there was no difference in the Al toxicity between the two pHs. Iron, on the other hand, seemed to be more toxic at pH 5. Despite its toxicity, iron did not stimulate mucus production by the gills at pH 5. Iron reduced the accumulation of Al into the gills at pH 6 but not at pH 5.