Selectivity of fish nutrition - the ability of fish to consume food organisms in a different ratio than they are available in the water body, some they prefer and others they avoid. Fish that feed on zooplankton (omul, pelada and rowan). Selectivity is poorly expressed, as it is difficult to filter out the desired organisms from the ingested volume of water. In benthophages, selectivity is quite clearly expressed. For example, carp avoid ostracods, although they are larger and more numerous than other crustaceans, sterlet choose chironomids, bream - mollusks.
Food can be divided into: favorite, occasional, and forced.
To quantify the selectivity of fish feeding, an appropriate index was proposed, which is the ratio of the percentage of a given group of food organisms in a food clump to the percentage of that group in the fauna of the water body.