Twenty-eight populations of brook trout (Salvelinus fontinalis) in Georgia were genetically compared using isozymes and their genetic relatedness determined. Eight populations (29%) were classified as southern based on fixation for CK-A2*122 allele, 2 (7%) populations were classified as northern based on fixation for CK-A2*100 allele, and the remaining 18 (64%) were northern-southern hybrid populations. All 8 southern populations shared some variant alleles with northern populations. Northern brook trout in Georgia had much greater genetic variation than southern brook trout, and hybrid populations were intermediate. Among the 8 southern populations and hybrid populations that are strongly southern, 2 major genotypes exist based on fixed or large differences at the sAAT-3* locus. Combinations of migration, non-random mating and selection are occurring, as many loci were not at Hardy-Weinberg equilibrium. Data and historical records indicated that stocking had little genetic impact when established brook trout populations were already present. Among the 8 southern populations, allele frequencies indicate 4 pairs of populations that are highly similar to each other. Logan Creek and Bryant Creek have similar allele frequencies and patterns of genetic variations. Similar allele frequencies and genetic variation patterns were also observed at Emory Branch and North Prong Left, Keener Creek and Gizzard Brand, and Rough Creek and High Shoals Creek.
