Experiments were conducted in three ponds and nine plastic swimming pools to determine the variation in growth rate of largemouth bass (Micropterus salmoides) during their first year of life. Known-age fish were obtained from artificially stripped and fertilized eggs and from the nest of one pair of largemouth bass. The fry were stocked into pools or ponds. Fathead minnows (Pimephales promelas) were stocked into three ponds and four large plastic pools as brood fish to provide offspring as forage for the bass which were added later. Golden shiners (Notemigonus crysoleucas) were stocked into the ponds after the bass were added. Fathead minnows, mosquito-fish (Gambusia a/finis) and golden shiners were added at intervals in the small pools after the bass were approximately one inch long, and in the large pools to supplement the original stocking of fathead minnows. Samples of approximately 10 bass were taken periodically. The weight and total length of each fish was measured and the fish was returned. When the experiments were terminated, weight and total length were again taken and sex was determined when this could be done without sacrificing the fish. Seventy-one to 243 bass were stocked as fry or one-inch fingerlings into each pond or pool. Survival to approximately one year of age varied from 1.0 to 34.5 percent. Variation in growth rate within individual pools or ponds ranged from 1.9X (largest individual weighed 1.9 times as much as smallest individual in the population) to 20.3X. Coefficient of variability ranged from 14.2 to 94.0. Variation between individuals of a population was, in general, closely correlated with both population density and rate of growth. Variation was greatest in those populations having the greater densities and the slower growing individuals. Differences in growth rate between the sexes could only be determined in the pond experiments as most bass in the pools did not reach sexual maturity during the study period. In all three pond populations, the males were larger than the females when the experiments were terminated. In Liles', Gay's and Knott's ponds the males averaged 188.0, 163.0 and 363.6 grams, respectively, while the females averaged 162.1, 149.4 and 328.9 grams, respectively. Males attained sexual maturity at a smaller size than the females.
