Ionoregulatory and endocrine responses to disturbed salt and water balance in Mozambique tilapia exposed to confinement and handling stress

This study assessed the endocrine and ionoregulatory responses by tilapia (Oreochromis mossambicus) to disturbances of hydromineral balance during confinement and handling. In fresh water (FW), confinement and handling for 0.5, 1, 2 and 6 h produced elevations in plasma cortisol and glucose; a reduction in plasma osmolality was observed at 6 h. Elevations in plasma prolactins (PRL177 and PRL188) accompanied this fall in osmolality while no effect upon growth hormone (GH) was evident; an increase in insulin-like growth-factor I (IGF-I) occurred at 0.5 h. In seawater (SW), confinement and handling increased plasma osmolality and glucose between 0.5 and 6 h; no effect on plasma cortisol was seen due to variable control levels. Concurrently, both PRLs were reduced in stressed fish with only transient changes in the GH/IGF-I axis. Next, the branchial expression of Na+/K+/2Cl− cotransporter (NKCC) and Na+/Cl− cotransporter (NCC) was characterized following confinement and handling for 6 h. In SW, NKCC mRNA levels increased in stressed fish concurrently with elevated plasma osmolality and diminished gill Na+, K+-ATPase activity; NCC was unchanged in stressed fish irrespective of salinity. Taken together, PRL and NKCC participate in restoring osmotic balance during acute stress while the GH/IGF-I axis displays only modest responses.