Effects of hypoxic stress on energy metabolism in red sea bream, Pagrus major, 1: Stress response and energy status in various tissues of red sea bream, Pagrus major, subjected to hypoxic exposure

Abstract

Young red sea bream, Pagrus major, were exposed to a gradual decrease in partial pres- sure of oxygen (PO2) down to 20 mmHg for 5 h, and then sustained under 20 mmHg PO2 for an additional 3 h at 19.9oC. Fish respiratory frequency slowly increased and attained a peak level at approximately 35 mmHg PO2, and then gradually decreased. Fish sank to the tank bottom about an hour after PO2 fell below 20 mmHg, and respiration began to arrest after another hour. Hematocrit value increased and mean cellular hemoglobin content (MCHC) decreased with increasing hypoxia load. Plasma cortisol and glucose levels were significantly augmented when respiratory frequency decreased. ATP, total adenylate (TA) concentration and energy charge (EC) in the hepatopancreas, in addition to TA in the kidney, were considerably diminished by hypoxia. However, this was not observed in the gill and brain of all fishes prior to respiratory arrest. In the hepatopancreas, levels of ATP, TA and EC notably declined as respiratory frequency decreased. These results show that the cortisol stress response to hypoxia is significantly induced with the decreased respiratory fre- quency. Decreased energy status in the hepatopancreas appears to be important and occurs with stress response as a metabolic depression in the whole body.