Studies on stress responses and recovery from removal in gilthead sea bream Sparus aurata (L.) using recirculated seawater system

The effects of serial cohort-removal stress on physiological responses in i mmature specimens of the euryhaline species, the gilthead sea bream Sparus aurata, were investigated (trial 1). In addition, physiological responses d uring recovery in tanks of 175 l (10.5 kg/m(3)) after a single (trial 2) or serial (trial 3) cohort-removal from a holding tank of l.m(3) (14 kg/m(3)) were examined. All trials were performed in a recirculated seawater system . Serial cohort-removal for 90 min. combined with a continuous pursuing (tr ial 1), caused a significant increase of plasma cortisol, glucose, osmolali ty, Na+, Cl- and pCO(2), and a significant reduction of pH, K+ and HCO3- in the remaining fish of the holding tank. These alterations in most of the p lasma parameters studied were progressive for 45-60 min and then remained a lmost constant. When undisturbed fish were netted and transferred (trial 2) , the levels of plasma cortisol, glucose, osmolality, Cl- and Na+ initially increased, exhibiting maximum elevations at 40 min and recovering within 2 h, At the end of a serial cohort-removal after 15 min, without chasing the fish (trial 3), the levels of plasma cortisol, glucose, Na+, Cl- and K+ di d not significantly differ from the control levels. However, during recover y from netting and transfer of fish disturbed by this serial cohort-removal , the levels of plasma cortisol and glucose recovered after 5 h. It is indi cated that serial cohort-removal, depending on its duration, may increase t he alterations in stress responses, especially the secondary ones, and prol ong: the extent of cortisol and glucose elevations. it was concluded, that serial cohort-removal of gilthead sea bream should be mild and short-term a nd could be repeated the same day allowing, however, a sufficient period fo r cortisol and glucose recovery. (C) 1999 Elsevier Science B.V. All rights reserved.