Aquatic Productivity and the Evolution of Diadromous Fish Migration

TLDR

Diadromous migration, in which fish move between freshwater and ocean habitats, has long been perplexing. When diadromous species distribution is mapped against global aquatic productivity, the paradox resolves: oceanic productivity dominates temperate zones favoring anadromous species, while freshwater productivity dominates tropical zones favoring catadromous species.

Abstract

Diadromous migration, in which some fish species migrate from freshwater and feed in the ocean (anadromous species) and others migrate from the ocean and feed in freshwater (catadromous), has long been perplexing. However, when the distribution of diadromous species is examined with respect to global patterns in aquatic productivity, this apparent paradox is resolved. The contrasting directions of migration can largely be explained by the relative availability of food resources in ocean and freshwater habitats. Oceans are more productive than freshwaters in temperate latitudes, and anadromous species predominate. In contrast, catadromous species generally occur in tropical latitudes where freshwater productivity exceeds that of the ocean.