Seasonal changes in the gonadotropic cells of the male threespine stickleback, Gasterosteus aculeatus L.

Abstract

Pituitaries from threespine sticklebacks (Gasterosteus aculeatus) sampled in the field in different seasons were studied using light and electron microscopy. At the start of breeding in May the gonadotropic cells demonstrated an increase in the amount of dilated granular endoplasmic reticulum cisternae and in the size of Golgi complexes, indicating increased synthetic activity. When the breeding season ended in August these features declined. In the period April to August there was a continuous decrease in the amount and size of granules stored in the gonadotropic cells. The size of the gonadotropic cell nuclei was larger in April than in the breeding season and at the end of breeding it declined further.