The influence of the environmental salinity on the prolactin (PRL) and growth hormone (GH) cells of the adenohypophysis of the grey mullet (Mugil cephalus) adapted to seawater (SW, 35 ‰) and fresh water (FW, 0-0.5 ‰) has been studied by immunocytochemical technique. The results indicated that PRL and GH cells of fish adapted to FW occupied a greater hypophysial region and have larger nuclear areas than those of SW-adapted fish. In addition, the activity of both
PRL and GH cells in FW ponds was higher than those of SW ponds. Consequently, the FW-adapted fish exhibiting higher condition factor (1.05 in FW, 0.96 in SW) and with higher percentage of protein content (61.41 % in FW, 48.23 % in SW).