The swimming ability of fish may be one of the most important factors affecting their capture by or escape from fishing gears. It has a bearing on capture processes by both active (such as trawls and purse seines) and passive (such as gillnets, longlines and traps) fishing gears. Swimming ability of fish varies from species to species and size of the fish and can be influenced by environmental factors such as water temperature. As a result, swimming ability of fish may affect the size and species selectivity of the gear and affect the seasonal and spatial differences in availability and catchability. This chapter will review the swimming ability of some commercial marine fish species and discuss the swimming behavior of these species in relation to their capture by, and, escape from, otter trawls and bottom-set gillnets.