Seasonal changes of the gill epithelia of Arctic char (Salvelinus alpinus) from a high mountain lake

Abstract

The gill structure of Arctic char from a low ionic (1-2 µmol Cl -) high mountain lake (2344 m above sea level) showed distinct seasonal changes. From spring to early winter chloride cells (responsible for ion uptake) were numerous, and during summer gill epithelia were highly hypertrophic resulting in a thick blood-to-water barrier. This gill morphology is typical for fish from soft water habitats and reflects osmoregulatory responses. In mid-winter, however, both chloride cell numbers and epithelia thickness were reduced and comparable to the situation in freshwater with high ionic contents. This pattern correlated with seasonal fluctuations of water chemistry. The most significant correlation was found with CO 2 which accumulated under the ice cover, reaching a tenfold oversatturation. The concentration of Ca, Na, and Cl varied only by a factor of two or less and the correlation with the epithelial thickness was much weaker.

Seasonal changes in blood cells of Arctic char (Salvelinus alpinus L.) from a high mountain lake

“…In addition, lymphocytes frequently contained swollen and damaged mitochondria and proved to be vulnerable to mechanical stress such as smearing on glass plates or centrifugation. As during winter the histological status of gills (Hofer et al, 2000) and liver of the fish (Hofer and Lackner, unpublished results) was better than in summer the decreased resistance of white blood cells can hardly be attributed to environmental stress. A higher lability due to their advanced age is more likely and confirms the results with erythrocytes.…”

“…During the ice-free period, however, the whole water body is saturated with oxygen. On the other hand, gill epithelia became hypertrophic during summer (Hofer et al, 2000), which may impact the branchial gas transfer (Bindon et al, 1994).…”

“…The oxygen content varied between somewhat more than 11 mg · L -1 in summer and a minimum of 5 mg · L -1 at the deepest point of the lake in winter. For more data on water chemistry see Köck et al (1995) and Hofer et al (2000).…”