Why are so many boreal freshwater fishes anadromous? Confronting ‘conventional wisdom’

Suggestions that anadromy predominates in northern high latitudes because boreal marine seas have high primary productivity are questioned. Instead, post‐Pleistocene invasion of far northern fresh waters, which became inhabitable as Pleistocene temperatures ameliorated, via coastal seas, is suggested as a primary cause for northern distributions of widely anadromous fish families. Also, cold temperature preferences may be implicated in determining the ranges of these families, as well as the inhospitability of far northern fresh waters and the lack of ecosystem space to support the huge populations of boreal anadromous fishes. Moreover, there are significant numbers of tropical anadromous fish species.