Sauvagine/urotensin I-like immunoreactivity in the caudal neurosecretory system of a seawater fish Diplodus sargus L. in normal and hyposmotic milieu.

We report the presence of sauvagine/urotensin I-like immunoreactive (SV/UI-LI) elements in the caudal neurosecretory system of a teleost (Diplodus sargus L.) collected from aquaria tanks of the Aquaculture Center (Talassographic Institut of CNR) of Messina or maintained in an hyposmotic milieu for different periods. In normal specimens, SV/UI-LI material was recognizable in discrete or little amounts both in Dahlgren cell cytoplasm and in their axons that reach the urophysis. On the contrary, the specimens transferred in an hyposmotic milieu showed a fast and dramatic increase of immunoreactivity mainly in neurohemal endings of the urophysis. This suggests a physiological role of caudal neurosecretory products on osmoregulatory mechanisms.