Interaction of temperature, dissolved oxygen and feed energy on ecophysiological performance of juvenile red drum

The red drum (Sciaenops ocellatus) is important for recreational fishing and aquacultural production in Texas' coastal waters and elsewhere in the nearshore Gulf of Mexico and in subtemperate to subtropical areas of the western North Atlantic Ocean. I performed indoor-tank and outdoor-pond experiments, in conjunction with automa ted respirometry and ecophysiological modeling, to assess interacting effects of temperature, dissolved-oxygen concentration (DO) and feed energy density on survival, growth, metabolism, and other measures of juvenile red drum performance. The main objective was to test an energy/metabolism tradeoff hypothesis, which states that growth of fish exposed to high temperatures can be limited by available feed energy; whereas, growth of fish exposed to lower temperatures can be limited by their metabolic capacity to exploit available feed energy. Also, I examined the influence of DO on this relationship and evaluated the effects of cyclical regimes of temperature and DO on fish performance. Insights from laboratory-based feeding trials were incorporated in experiments conducted in hatchery ponds to assess effects of oxygen supplementation and dietary additives - nucleotides and prebiotics - on performance in a more natural setting. In examining these issues, various technologies were developed. These included a computer-based apparatus for autonomously inducing cyclical regimes of temperature and DO in experimental tanks over an extended period of time. Additionally, I developed a soft feed with low energy-density to simulate natural forage. Experimental results supported the principal research hypothesis: At high temperature and DO, ecophysiological performance of juvenile red drum was enhanced by feeding to satiation with a high-energy feed (15.9 kJ/g) versus with a foragesimulating feed having lower energy density (4.1 kJ/g). Cyclical regimes of temperature and DO - as imposed in my particular laboratory experiments -did not impart growth benefits; however, the potential for enhanced growth via an appropriate cyclical environmental regime remains intact. Results from outdoor-pond experiments were consistent with laboratory results; however, the strong positive effect of feed energy density overwhelmed potential effects of dietary additives or oxygen supplementation on growth.