An unusually small, mature whitefish which appeared to be identical to the lake whitefish, Coregonus clupeaformis, was found in 22 lakes in northwestern Maine in 1957-62. In most lakes the “dwarfed” form was found sympatric with “normal” lake whitefish, but populations that are completely dwarfed were found in three lakes. Distinct differences have been found in the size and age at which the two forms of whitefish become sexually mature, in their rate of growth, in their morphology, and in their erythrocyte antigens. Information on spawning habits provides further evidence of two separate breeding populations. All evidence leads to the conclusion that the two forms of lake whitefish are discrete, and that at least a partial barrier to gene flow exists between them. The differences between the two forms are highly variable from lake to lake, making any conclusions as to their systematic relationship tenuous. It is suggested that this variation may be due in part to varying degrees of convergence of two whitefish forms that once diverged from a common progenitor.
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