Populations of two congeneric species of southwestern Atlantic sciaenid fish, Menticin-hus americanus and Menticin-hus littoralis, analysed electrophoretically to detect isoenzyme variability, showed very little genetic variation and a moderately high similarity in their allelic composition. A total of 22 alleles encoded by 17 loci were observed. Interspecific variability were found for the loci G6pdh-A, G6pdh-B, Hbdh-B, Mdh-B and Sod-A. Intraspecific variation was observed only for Mdh-B in M.

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... littoralis. The genetic similarity between M. americanus and M. littoralis (INEI +0.76) is congruentwith the high level of morphological similarity showed by these two congeneric species.