Transferrin variants were examined in population samples of fish, locally known as jaraquis, Semaprochilodus taeniurus and S. insignis. Both species were sampled on two occasions from two geographical areas in the Amazon region. The two species showed no common transferrin type. The 122 specimens of S . taeniurus showed three genotypes encoded by two codominant alleles at the transferrin gene locus ( T n . The 69 specimens of S. insignis showed another two transferrin alleles.Hence the different Tf genotypes support their taxonomic differences, and are predictably capable of identifying any suspected hybrid species. No hybrid was found.

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