Growth parameters in northern largemouth bass Micropterus salmoides salmoides raised near their upper thermal tolerance for 28 days

This study assessed growth, feed conversion efficiency, and fatty acid composition of three size classes of northern largemouth bass Micropterus salmoides salmoides (80 g, 105 g, and 137 g) subjected to a 35 degrees C water temperature for 28 days. A completely randomized design was conducted, with ten fish per tank and treatments triplicated. The trial was conducted in 180-L tanks in a recirculating system. Fish were fed a commercial diet formulated for largemouth bass consisting of 48% protein and 18% lipid at approximately 0800 and 1500 h daily. The experimental period lasted for 28 days. Water temperature was a significant contributor to the feeding and growth results observed in this study. While the 137 g group did experience some growth, the observed growth was not biologically significant during this study. The percent body weight consumed by all treatment groups was less than 0.21% day -1. Feed conversion was best for the 137 g group at 4.0 +/- 0.44 compared to 5.5 +/- 2.57 and 5.8 +/- 2.77 for the 80 g and 105 g groups, respectively. Fatty acid profiles of the groups remained similar except eicosapentaenoic acid, which was lower in the 80 g fish. This study was the first to examine the growth of northern largemouth bass at temperatures exceeding 32 degrees C and suggest extended periods of exposure to 35 degrees C or higher water temperatures resulted in thermal stress and the inability of these fish to grow at the rates necessary to make them profitable for commercial producers.