Abstract
Histological changes of the ultimobranchial gland of the masu salmon, Oncorhynchus masou, were examined with reference to the serum calcinm and osmotic concentrations at different ecological phases through the life history of the fish. In smolts, the giand cell was higher than that in parrs of the same length. The mitoses were active in large parrs, smoles, and young salmon in the coastal sea, while inactive in maturing salmon. In fresh water ascending salmon, the arrangement of the gland cells was compact; the nuclei elongated in profile and the cytoplasm became more basophilic. Abundant blood capillaries became apparent in the surrounding connective tissue. In pre-ovulating females, the height of the epithelial cell reached a maximum; the cells exhibited a bypertrophy and included extensive infranuclear ergastoplasm, corresponding to the well-developed granular endoplasmic reticulum. Such characteristic features were not observed in the male glands. Degeneration of the epithelial cells in the female glands was noted at ovulation. Alterations of the serum calcium and osmotic concentrations seemed not to be correlated with the above-mentioned morphological changes of the ultimobranchial gland. The findings suggest that the gland may play some sex-related role in the females.
