Selectivity (selectivity) is the ability of fishing gear to take (select) from the available stock a certain number of fish differentiated by species and size groups, sex, age.

Selectivity of fishing gear is the ability of fishing gear to select a certain number of fish from the herd, shoal, or part of the population being fished. It depends on the ratio of fish girth to mesh perimeter and the number of fish in the fished part of the population. There are 4 types of selectivity of fishing gear: by species, size, sex and age of fish.

The selectivity of a fishery is determined by two things: the selectivity of fishing gear and the behavior of fish (individuals of different ages belonging to the same species and individuals of the same age but in different biological states). The design of each gear or fishing method must take into account the properties of the fish for which the gear or method is intended.