Putative role of adenohypophysis in the osmoregulation of tilapia larvae (Oreochromis mossambicus; Teleostei): an ultrastructure study.

Ultrastructure of the secretory cells in the adenohypophysis of tilapia (Oreochromis mossambicus) larvae hatched in fresh water or sea water was compared. Adenohypophysis of newly hatched larvae of tilapia is a short columnar body attached to the ventral floor of the diencephalon. The adenohypophysis is at its early differentiation stage, i.e., various types of secretory cells are still undistinguishable. Only part of the cells in the putative rostral pars distalis look like typical endocrine cells, containing well-developed rough endoplasmic reticulum, Golgi apparatus, and numerous secretory granules. The average size of secretory granules in freshwater-hatched larvae is significantly larger than those in seawater-hatched larvae (12,936 +/- 2854 nm2, N = 11 vs 3375 +/- 810 nm2, N = 10), suggesting some role of adenohypophysis in the osmoregulation of the early developmental stage of teleosts.