EFFECT OF DECREASED ENVIRONMENTAL SALINITY ON GROWTH-HORMONE CELLS INTHE GILTHEAD SEA BREAM (SPARUS-AURATA)

The effect of decreased environmental salinity on growth hormone produ cing cells (GH cells) of the adenohypophysial proximal pars distalis h as been studied in the gilthead sea bream (Sparus aurata L.) adapted t o sea water (SW, 980 mosmol kg(-1)) and brackish water (BW, 200 mosmol kg(-1)). A combined immunocytochemical, morphometric and electron mic roscopic study was carried out. GH cells of fish adapted to BW occupie d a greater hypophysial volume (about 21% of the total hypophysial vol ume in BW, 17% in SW) and had a larger nuclear area (mean 16 mu m(2) i n BW, 13 mu m(2) in SW) than GH cells of SW-adapted fish. The immunore activity against a salmon GH-antiserum was lower in BW (mean optical d ensity 142 in BW, 159 in SW). Ultrastructural characteristics of GH ce lls of BW-adapted fish were distended rough endoplasmatic reticulum an d large secretory granules (about 216 nm in diameter for BW, 209 nm in SW). Volumetric, densitometric and ultrastructural evidence suggested that the synthesis and release of GH were activated in S. aurata adap ted to hypo-osmotic environment.