Comparative oxygen consumption and metabolism of striped bass Morone saxatilis and its hybrid M. chrysops ♀ x M. saxatilis ♂

It has been reported that metabolic rates of striped bass Morone saxatilis and hybrid striped bass M. chrysops x M. saxatilis d are different. A series of experiments were conducted to further characterize oxygen consumption and metabolism of striped bass and its hybrid, the sunshine bass. Oxygen consumption was measured to determine standard and routine metabolic rates of striped bass and hybrid striped bass in a freshwater, flow-through tank system. Additionally, blood chemistry stress indicators of the two bass groups were compared in both fresh and brackish water. Hematocrit (% PCV) and hemoglobin were measured in order to compare oxidative efficiencies of the bass. Plasma glucose, chlorides, and cortisol levels were measured to compare the relative stress status of the two bass types reared under experimental conditions. No significant differences were found in average daily oxygen consumption between striped bass and sunshine bass for either standard metabolism (P = 0.92), or routine metabolism (P = 0.86). Standard metabolic rates of oxygen consumption were 69 +/- 4.1 and 68 +/- 3.5 mg O-2/kg(3/4) bw/h for sunshine bass and striped bass respectively. Routine metabolic rates were 132 +/- 30 and 125 +/- 30 mg O-2/kg(3/4) bw/h for sunshine bass and striped bass respectively. While there were no significant differences in oxygen consumption between species, normal feeding activity generally resulted in increased oxygen consumption by the fish. Striped bass had significantly lower hematocrit values (P = 0.0001), but significantly higher hemoglobin concentrations than sunshine bass maintained in freshwater (P = 0.0001). Striped bass had significantly higher (P = 0.0001) levels of plasma glucose compared to sunshine bass (176 +/- 8.6 vs. 103 +/- 5.6 mg/dL respectively). Plasma chloride levels for striped bass (123 +/- 1.9 mEq/L) were significantly higher (P = 0.041) than plasma chloride levels of sunshine bass (117 1.7 mEq/L). Plasma cortisol levels were significanty higher (P = 0.0081) for striped bass (147 +/- 8.4 ng/mL) compared to sunshine bass (119 +/- 5.6 ng/mL) when reared in freshwater. When maintained in brackish water, sunshine bass had significantly higher hematocrit values (P = 0.0001), and hemoglobin concentrations (P = 0.0012) when compared to striped bass. However, sunshine bass had significantly higher hemoglobin concentrations (P = 0.0012) when compared to striped bass. In addition, plasma glucose levels were significantly lower (P = 0.0079) for sunshine bass (79 +/- 4.1 g/dL) when compared to striped bass (115 +/- 11 g/dL). There were no significant differences between the bass in levels of chlorides or cortisol. No differences were detected in oxygen consumption. However, hybrid striped bass may have more efficient oxidative metabolism due to elevated hemoglobin concentrations. While striped bass hemoglobin values tended to be higher in brackish water than in freshwater, sunshine bass hematocrit or hemoglobin values generally were significantly higher than striped bass in both fresh and brackish water. Based on these results, hybrid striped bass may be capable of directing more energy towards growth than striped bass due to more efficient oxidative metabolism and lower losses of energy related to increased stress.