Morphological Variation of the Pituitary-interrenal Tissue of the Mullet Fish (Mugil cephalus) Reared in Different Habitats.

The current study was designed to illustrate the histological variations of pituitary gland andinterrenal tissue of mullet fish (Mugil cephalus) reared in fresh and marine waters. In thisstudy, the pituitary gland of Mugil cephalus consisted of adenohypophysis andneurohypophysis. Three regions were observed in adenohypophysis, rostral pars distalis(RPD), proximal pars distalis (PPD) and pars intermedia (PI). There was no adrenal gland inMugil cephalus resemble mammals but interrenal tissue and chromaffin cells were locatedin the wall of posterior cardinal vein in the head kidney. Light microscope and staticallystudies showed an increase in the square surface area of RPD including the surface areas ofthe prolactin (PRL) cells adrenocorticotrophs (ACTH cells) in adenohypophysis andinterrenal tissue in the head kidney of the freshwater fish than marine fish. These resultsindicate the important role of prolactin, adrenocorticotropin and cortisol hormones inosmoregulation in the freshwater Mugil cephalus and help in stress and habitat adaptation.