[Ultrastructure of prolactin cells of three Mugilidae during adaptation to fresh-water (author's transl)].

The behaviour of three species of Mugilidae (Mugil ramada, Crenimugil labrosus and Mugil auratus) during adaptation to fresh water is very different. Those differences may be explain by variants of their prolactin cells activity. The adaptation of Mugil ramada and Crenimugil labrosus to fresh water is easy and last over a long time; the prolactin cells, with a slow activity in sea water, become during adaptation more active. In Mugil auratus in sea water, prolactin cells present already a sign of strong activity. After transfert in fresh water, they appear to be unable to increase their activity. The adaptation of this species is difficult and short-lasting.