Morphological studies on the growth hormone cells in the pituitary gland of the nine-spined stickleback, Pungitius pungitius L.

Base-line data is presented on growth hormone cells in adult, nine-spined sticklebacks, Pungitius pungitius L. The cells are smallest in June-August, when adult animals are oldest and many large fish are dying. It may thus be the wrong time for seawater-transfer experiments designed to alter the secretory state of these cells. Starving fish for 3.5-4 weeks in February and in September-October did not markedly affect growth hormone cell numbers, staining properties or size. A detailed morphometric analysis of growth hormone cell ultrastructure is presented. The cells are characterized by their electron dense secretory granules, 150-750 nm in diameter that occupy 33% of the cell volume. Neither the Golgi apparatus nor the rough endoplasmic reticulum are present in large amounts (volume densities 2.9% and 8.1% respectively), but the rough endoplasmic reticulum is conspicuous because of its flocculent cisternal contents. Both 'light' and 'dark' growth hormone cells were found. The dark cells have a densely staining cytoplasmic ground substance and abundant, closely packed secretory granules. The morphometric data is compared with similar information that is available for the related three-spined stickleback, Gasterosteus aculeatus.