THE GROWTH OF LARGEMOUTH BASS, MICROPTERUS-SALMOIDES (LACEPEDE), UNDER CONSTANT AND FLUCTUATING TEMPERATURES

Growth of largemouth bass, M. salmoides, was tested under constant (15.degree. C, 29.degree. C) and cyclic (18 h at 15.degree. C, 6 h at 29.degree. C) temperature conditions. Six groups of 10 fish each were tested; 1 group under each constant condition, and 4 groups in the thermocycles. The 4 latter groups differed in the timing of their feeding; 1 group each was fed at the start and middle of the warm and cool periods, respectively. All groups were fed to near-satiation. The fish fed at the start of the warm cycle and start cool group grew most rapidly, followed by the constant warm, mild warm, mid cool, and constant cool groups. These data were evaluated in relation to vertical migrations of fish to test the physiological enhancements that may be important to vertical migrations. Apparently, thermocycles allow more rapid consumption of food than constant cool conditions and lower metabolic rates than constant warm conditions, which allows some fish to grow more rapidly under thermocycles than under constant conditions at either extreme of the cycle. The timing of feeding in relation to temperature in the thermocycle is important in the degree of growth enhancement.