[Ultrastructure of prolactin cells and survival of Gambusia sp. (teleost fish) in deionized water enriched in calcium or sodium].

The ultrastructure of the prolactin (PRL) cells of Gambusia was studied in animals kept in deionized water (EDes) and in EDes supplemented either with Ca2+ (10,2 and 15,3 mM) or with Na+ (10,2 and 15,3 mM). In environments supplemented with CaCl2 the maximal survival was 40 days. The stimulation of PRL cells was similar to that described in EDes. On the contrary, in environments supplemented with NaCl, 50% of the animals are still alive after 45 days. PRL cells are slightly stimulated and their ultrastructural aspect is similar to that observed in controls kept in freshwater. The significance of these results is discussed in relation with our present knowledge of the pituitary control of osmoregulation in teleost fish.