The muscle myogen patterns obtained by starch gel electrophoresis of the Dolly Varden and eastern brook trout (Salvelinus), the rainbow and steelhead trouts and the Atlantic salmon (Salmo), and the coho, spring, chum, sockeye and pink salmon (Oncorhynchus) are compared. The myogen protein patterns are clearly distinct for each species of fishes studied, except for the rainbow and steelhead trouts, and constitute a remarkably constant property which can be employed to differentiate between species and for other useful purposes. The specific and generic inter-relationships have been analyzed by these patterns and developed as further criteria for classification purposes and are discussed in conjunction with currently accepted beliefs.