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 immature specimens of the euryhaline species, the gilthead sea bream Sparus aurata, were investigated (trial 1). In addition, physiological responses during 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 1 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 (trial 1), caused a significant increase of plasma cortisol, glucose, osmolality, Na +, Cl − and pCO 2, and a significant reduction of pH, K + and HCO 3 − in the remaining fish of the holding tank. These alterations in most of the plasma parameters studied were progressive for 45–60 min and then remained almost 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 + did not significantly differ from the control levels. However, during recovery 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 indicated that serial cohort-removal, depending on its duration, may increase the alterations in stress responses, especially the secondary ones, and prolong the extent of cortisol and glucose elevations. It was concluded, that serial cohort-removal of gilthead sea bream should be mild and short-term and could be repeated the same day allowing, however, a sufficient period for cortisol and glucose recovery.