Migrations of fish species are often very long (in both time and space) and costly in terms of energy. Thus, efficient use of available energy is of great importance and various adaptations or morphology and behavior have resulted. These are especially significant for diadromous species, which encounter large variations in buoyancy, salinity, temperature, and flow conditions during their life cycles, which include large-scale migrations. A mathematical approach to fish migratory adaptations is utilized to analyze observed behavioral patterns and to predict effects of changing environmental pressures. The study is based on the hydrodynamical and mechanical principles of fish locomotion, feeding, and predator-prey interactions. Existing work is reviewed with the goal of identifying areas of future observational and theoretical research applicable to the understanding of the behavioral strategies of these species, many of which are commercially important.