Results are presented of a comparative study of the spatial and temporal structure of fish species from the standpoint of biochemical population genetics. Local fish stocks within historically established natural boundaries are considered as genetically stable population systems, in contrast to the elementary populations, which are variable structural components of such systems. The general principle in maintaining a rational fish industry is formulated on the basis of an approach to the population system as a whole, to distribute the appropriate efforts among all components of its structure.Key words: biochemical population genetics, stock concept of fish, optimal fishing industry