Genic Polymorphism of Tetrazolium Oxidase in Bluefin Tuna, Thunnus thynnus, from the Western North Atlantic

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Abstract
Blood and tissues from bluefin tuna (Thunnus thynnus) contain several electrophoretically distinct forms of the enzyme tetrazolium oxidase. Every fish exhibits one of three oxidase phenotypes: a single band at either of two positions on the gel or both bands with a third midway between them. The pattern comprising three bands occurs in both males and females. Frequency distributions of phenotypes conform to Hardy-Weinberg distributions and apparently are not related to fish size. We conclude from these facts that bluefin tetrazolium oxidase contains two protein subunits and that phenotypic differences among individuals reflect segregation of two codominant autosomal alleles. Frequency distributions of phenotypes in three areas of the western North Atlantic do not differ significantly.