The Genesis of Fishes from the Order Salmoniformes

The genesis of members of the order Salmoniformes needs elucidation in order to identify the trend of morpho-ecological and genetic evolution of these fishes and also clarify the patterns of their biological diversification. Adherents of the marine genesis hypothesis consider Salmoniformes as marine fishes that have transferred their reproduction to fresh waters, while those advocating the freshwater origin hypothesis suggest these to be freshwater fishes that have occupied feeding grounds in the marine environment. An analysis of literature data has shown the assumption about the transfer of feeding grounds to the marine environment by salmoniforms as untenable, whereas development of spawning in fresh waters by fish of the marine genesis is a quite common and widespread phenomenon. According to results of fossil record examinations, the center of origin of salmoniform fishes is the northern Pacific Ocean, where their marine ancestor became anadromous no later than in the early Paleogene. Subsequently, after the opening of the Bering Strait at the Miocene–Pliocene boundary, anadromous salmoniforms migrated to the Polar Basin and North Atlantic where the secondary centers of speciation emerged.