A RECENT MARINE ANCESTRY FOR DIADROMOUS FISHES - SOMETIMES YES, BUT MOSTLY NO

Diadromy in its three forms (anadromy, catadromy and amphidromy) neces sarily involves fish spending part of their lives in the sea. It is no t uncommon contention that diadromous fish have a recent marine ancest ry and that they are in the process of moving from a marine to a fresh water lifestyle. However, analysis of the distribution of diadromy in fishes suggests that, for most species, it is an ancient life history style though, for a few, a recent marine ancestry seems plausible. In general, there is no reason to consider diadromy anything but a stable and successful life history style, and no reason to regard it as tran sitional between marine and freshwater habitats.