Abstract
The pond-cultured annual salmonid fish, the Ayu, Plecoglossus altivelis T. & S., was maintained under the artificial controlled photoperiodicity, and the survival time of the fish was prolonged considerably beyond the natural life span of this species. In the present paper, merely histological description was given of the endocrine glands of the fish. The shape of the pituitary gland shows a remarkable deformity, and many lacunae were occurred in the adenohypophysis, particularly in the rostral zone of pars distalis. The glandular cells, including many of dilated cells, located in the dorsal region of the proximal zone of pars distalis, were in the process of marked degeneration. The figure of the thyroid gland appears to be hypofunction and degeneration. Marked expansion of the head kidney was encountered, and the adrenal cortical tissue is composed of hyperplastic masses of acidophiles and of basophiles. The superficial layer of the head kidney indicates the state of severe necrosis. Inside the cardinal vein, there appears a strange structure which might be the hemangio-endothelioma. Whole ovarian eggs were remained in a state of preovulation, and underwent the process of degeneration. Various stages in the course of formation of corpora lutea were seen. Notable lymphosarcomatous nodules, varying in size, were detected in the ovary. The atretic eggs under the process of formation of corpora lutea were surrounded by fibrous connective tissue and reticulum which maintain many lymphocytes. Sometimes, partial necrosis was developed in the central region of a large tumorous growth. Possible relation between the light rhythm and the endocrine unbalance was discussed.
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