Comparative energetics of striped bass (Morone saxatilis) and hybrid (M. saxatilis×M. chrysops) juveniles

Abstract Survival, growth, and energetics of striped bass and striped bass×white bass hybrids, 70–120 days of age, were compared at three formulated daily ration levels of 2.5%, 5% body weight and ad libitum. Significantly higher growth rates were obtained with increasing ration levels for both genetic groups. Hybrids had significantly higher growth rates than striped bass at all ration levels. At the higher ration levels, hybrid growth surpassed striped bass, which were initially older and significantly heavier, at an earlier age during the 50-day culture period. Survival rates of all treatment groups were high (89–100%). Energy budget evaluations for the feeding levels (2.5% and 5%) demonstrated that both genetic groups had similar energetic losses through feces ( F =10.8% of the total energy intake). At the 2.5% ration, metabolism ( M ) accounted for 38.9% vs. 48.4% while growth ( G ) accounted for 42.2% vs. 32.2% of the energy intake for hybrids and striped bass, respectively. Similarly for the 5% ration, M was 43.2% vs. 56.8% and G was 39.8% vs. 25.7% for hybrids and striped bass, respectively. Hybrids had lower metabolism (10–12%) with respect to energetic needs and higher growth rate (10–14%) than did striped bass at both feeding levels. Therefore, hybrids grew faster not because of a better assimilation efficiency or a greater appetite, but because of a higher energy available for growth after metabolism.