INFLUENCE OF THE ENVIRONMENTAL SALINITY O N MELANOTROPIC CELLS IN THEGILTHEAD (SPARUS-AURATA L)

The influence of the environmental salinity on the MSH cells of the pa rs intermedia in the euryhaline teleost Sparus aurata has been investi gated. Control animals stayed in sea water (39 parts per thousand sali nity), and experimental fish in brackish water (7 parts per thousand s alinity) for two months. For light microscopy, pituitaries were fixed with Bouin fluid and embedded in paraffin. For electron microscopy the y were fixed with Karvnosky and embedded in Araldite. Sections were st ained with histochemical procedures and immunocytochemistry using an a ntiserum against human ACTH (1-24). The immunoreaction intensity was m easured by microdensitometry, the nuclear area and granule size by pla nimetry, and the volume occupied by the ACTH cells by volumetry. Where as the adaptation to brackish water decreased the immunoreactivity to anti-ACTH serum on the MSH cells, the volume and the nuclear area of t hese cells increased although without statistical significance. These results suggest that the adaptation to hypoosmotic environment elicits an increase in the synthesis and release of MSH and ACTH.