The effects of iron, humic acids and low pH on the gills and physiology of Brown Trout (Salmo trutta)

One-summer-old brown trout (Salmo trutta) were exposed to iron and humic acids at pHs 5 and 6 for two to three days in the laboratory. The oxygen consumption of the fish was measured after the exposure whereafter the gill and blood samples were taken. Brown trout gills were damaged in the exposure to iron at both pHs, more so at pH 5. Morphometric analysis showed that the fusion of the lamellae and hypertrophy of the epithelial cells significantly increased the diffusion distance across the gills. The precipitation of iron on the gills may also have increased the diffusion distance which had a negative effect on the oxygen uptake of the fish. Gill damage also impaired ion regulation seen as low Na+ and Cl- concentrations in the plasma. The blood glucose concentration increased, indicating stress in the fish. Humic acids in the water containing iron had an ameliorating effect on the ion regulation as well as the oxygen uptake but they did not completely prevent hypertrophy in the gills.