[Ultrastructure of the interrenal gland in young beluga in fresh water and during adaptation to salt water].

Two groups of cells (light and dark) were found in the interrenal gland of the young beluga from the fresh-water. Ultrastructural differencies are presumably associated with different functional activity of cells. 12 hours after the transfer of fishes to the sea water, the interrenal cells appeared to be most active with significant elevation of volumetric density of mitochondria and endoplasmic reticulum. After 8 days in the sea water, dark cells were found seldom; a great number of small lyposomes and large myelin-like figures were observed in the cytoplasm of the light cells. The volumetric density of mitochondria and of the reticulum was seen decreased. The functional activity of interrenal gland of the young beluga was lower after 8 days than after 12 hours in the sea water, but higher than in the fresh-water.