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The growth hormone gene has been used to infer phylogenetic relationships in fishes, and in closely related species the intronic sequence has shown particular value in discriminating among taxa. We examined the growth hormone gene in the esocid family by cloning the fourth intron of the growth hormone gene from all five esocid species. Our initial analysis identified a 33-nucleotide minisatellite in the fourth intron that is present in copy numbers ranging from seven to 16 among the various species. Database searches indicate that this minisatellite is present only as a single copy element in all of the salmonids, indicating a recent expansion in the esocid species since their divergence from a common ancestor. The minisatellite was not detected in any other growth hormone sequences available at the time of this writing. Furthermore, point mutations and deletions in the esocid minisatellites indicate a model for the evolution of this genetic element and corroborate existing molecular phylogenies for the five members of this genus.