Abstract

Data on the size and shape of fish schools, number, size, and species composition of individuals included in them have been considered. The largest schools, numbering up to hundreds of thousands of individuals or more, are formed by mass marine pelagic fish. The shape of fish schools of the same species is extremely diverse and changes rapidly, depending on the age and size of the fish, their mobility, condition, and other features. The classification of schools has been given—migrating (polarized), feeding, spherical (globular) and others. Schools can become denser or sparse, change the depth of swimming, break up and joint with neighboring ones. The variability of the linear sizes of fish schools and the number of individuals included in them reflects the high plasticity of schooling behavior and its susceptibility to the influence of various factors. Schools are characterized by high homogeneity of the species and size composition of fish and the absence of individual differences in fish. In some cases, schools may consist predominantly of female or male fish. Uniformity is the most important characteristic of fish schools and indicates assortativeness when fish unite into schools. The greatest homogeneity is characteristic of migrating schools of pelagic fish. Multi-species schools are most often formed by juvenile fish.