PRELIMINARY STUDIES ON SERUM CORTISOL AS INDICATIVE OF STRESS IN NILE TILAPIA (OREOCHROMIS NILOTICUS)

Abstract

The intensive fish culture procedures are stressors "per se". Although intensive aquaculture in southern Brazil has had a great development in the last years, the knowledge about stress effects in fish production continues insipient. The Nile tilapia (Oreochromis niloticus) has been the preferable species for commercial aquaculture. The aim of the present study was to determine the Nile tilapia response to spatial restriction in cages, added or not by a standard stress (anoxia) repeated during 21 days. The anoxia was provoked by 30 seconds cages emerged daily. Serum cortisol level was used as an evaluating parameter of stress in this species. One hundred and twelve adults Nile tilapias were kept in plastic cages, divided in two treatments with four replications each. The treatments were: T1 - fish submitted to standard stress, and T2 - control, fish not submitted to standard stress. There was no statistical difference in serum cortisol values between treatments. In conclusion, stress provoked by spatial restriction and establishment of hierarchy into both treatments did not show statistical difference in relation to serum cortisol levels provoked by the standard stress. New studies are being developed to better determine stress response of Nile tilapia.