| Abstract: | Approximately one-half million Florida largemouth bass Micropterus salmoides floridanus (FLMB) advanced fry were stocked into Aquilla Lake (1,330 hectares) between 1983 and 1985. The purpose of this study was to evaluate these successive annual FLMB stockings into this new Texas reservoir, and assess subsequent introgression with the resident population of northern largemouth bass M. s. salmoides (NLMB). Over a three-year period, allozymic variation at four enzyme-encoding loci and age were determined for 1,210 largemouth bass M. salmoides. With the formation of the 1986 year-class, FLMB and hybrid bass were numerically (72%) the dominant phenotypes in the population. At that time, the frequency of FLMB alleles expressed at the Idh-B and Aat-B loci was 52%. Although the subspecies hybridized in 1985 and 1986, the largemouth bass population did not conform to expected Hardy-Weinberg genotype proportions at Idh-B and Aat-B. Three factors were examined that partially explained Hardy-Weinberg disequilibrium and FLMB genomic contribution to the population: 1) partial temporal subspecies spawning segregation occurred, as NLMB tended to breed earlier in the spring than FLMB; 2) higher survival rates were evident for FLMB and F₁ hybrids than for NLMB; and 3) FLBM growth potential was greater than NLMB after age-2 which probably conferred a foraging and size-dependent fecundity advantage for these fish. Thermal conditions in Aquilla Lake were generally colder than those observed for FLMB populations previously sampled by other workers in peninsular Florida, but there was no evidence of genetic deterioration in the Aquilla Lake largemouth bass population following FLMB stocking. Based on these observations, regression equations predicted that the largemouth bass population in Aquilla Lake will become nearly fixed for FLMB alleles by 1992. A skewed sex ratio containing predominantly female fish was evident for F[subscript x] intergrades. Otolith size and time of annulus formation varied between subspecies. A decrease in FLMB feeding activity was observed at water temperatures below 12° C, suggesting prolonged exposure to cold water may reduce FLMB growth, condition, and survival. The duration of cold water temperatures during winter may be an important environmental factor determining the success of Florida largemouth bass stockings. |
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