Histological changes in the organs and tissues of the gobiid fishes throughout their life-span. VII. Seasonal changes in the hemopoietic organs of the forktongue goby.

Abstract

The hemopoietic organs of the forktongue goby, Chaenogobius urotaenia, were examined histologically with emphasis on the changes in the interrenal tissue during sexual maturity. In adult fish, the greatest enlargement of the parenchymatous tissue of the thymus with an increase in the number of small lymphocytes occurs in July, while the greatest number of small lymphocytes in the spleen and head kidney occurs one to two months later. In the underyearling fish, the parenchymatous thymus reaches its highest activity at the time of ascending the river from July to August, and lymphopoiesis in the spleen and head kidney become highest about two months later, i. e., in October. The cyclic pattern of the activity of these organs in the underyearling is fairly identical with that of the adult form. The interrenal cells of adult fish reach their greatest size just before the breeding period, and, conversely, are smallest from August to September. The recovery phase is detected when the gonadal development becomes active again. A nearly identical situation of the interrenal gland is seen in the underyearling fish. The cyclic pattern of the changes in the interrenal cells is quite opposite to that of the changes in the number of small lymphocytes in the spleen and head kidney as described in the flathead goby, Luciogobius guttatus.