Effects of hypoxia and subsequent recovery on turbot Scophthalmus maximus: hormonal changes and anaerobic metabolism

Hormonal changes, substrate mobilization and energy metabolism were studied in turbot Scophthalmus maximus exposed to 3 hypoxic conditions (oxygen partial pressure in water, PwO2 = 90, 60 and 30 mm Hg) followed by recovery under normoxia. Measurements of the blood pH, total CO2 concentration, arterial oxygen partial pressure, hematocrit, glucose, lactate, and ‘stress’ hormones (cortisol, adrenaline and noradrenaline) plasmatic concentrations were performed. Highenergy phosphorylated compounds, glycogen, glucose and lactate concentrations were also determined in liver and white muscle tissues. Exposure to 90 or 60 mm Hg did not induce any major physiological change, as hyperventilation by itself could compensate for the decrease in water oxygen tension. At 30 mm Hg, marked increases in cortisol, adrenaline and noradrenaline concentrations, associated with a decrease in blood arterial oxygen partial pressure, were observed. During exposure to 30 mm Hg, turbot resorted to anaerobic metabolism, resulting in liver glycogen depletion and lactate production. This mechanism appeared to be efficient enough to produce energy, as no significant change in phosphorylated compounds and adenylate energy charges in muscle and liver could be observed. These results indicate an absence of metabolic depression in turbot down to 30 mm Hg and confirm the high capacity of this species to cope with low water oxygen tension.