Individual growth and foraging responses of age-0 largemouth bass to mixed prey assemblages during winter

We conducted an outdoor pool experiment at a mid-temperate latitude (Ohio, 40degreesN) to determine how commonly occurring prey assemblages affect individual foraging and growth of individually marked, age-0 largemouth bass during winter. The treatments were low prey, bluegill prey only, macroinvertebrates only, and bluegill plus macroinvertebrates. Across all treatments, growth in mass ( g) was unrelated to body size. Conversely, small individuals lost more energy (kJ) than large counterparts in all but the macroinvertebrate-only treatment. With low prey, overall growth of largemouth bass was negative, with losses varying among individuals by 30% and 60% for mass and energy content, respectively. Counterparts in bluegill-only pools also consistently lost mass and energy, with less variability (15% mass; 30% energy). In the macroinvertebrate-only treatment, 31% of individuals gained mass, reflecting the greatest range in mass (100%) and energy ( 60%) change. With macroinvertebrates plus bluegill, overall growth was generally negative, with intermediate variance among individuals. Variation in growth among individuals typically increased with the frequency that prey occurred in diets during sampling. Apparently, some individuals were inactive, foraged infrequently, and consistently lost intermediate quantities of mass and energy. Others were active and foraged with variable success. Because activity and growth vary among individuals as a function of prey composition during winter, prey assemblages during this season will affect patterns of first-year survival and cohort strength.