From Ancient Greek ἰχθύς, "fish"; λόγος, "word".

Ichthyology - a section of zoology that studies the biology of fish and fish-like creatures (systematics, structure and function of organs, distribution, lifestyle, relationships with abiotic and biotic environment, population, practical importance).

The section of vertebrate zoology that studies fishes, their structure, functions of their organs, lifestyle at all stages of development, distribution of fishes in time and space, their systematics, and evolution. Ichthyological research contributes to the rational management of fisheries, ensuring the development of fisheries and fish farming. The versatile study of fishes has made it possible to make a number of important generalizations: on the problem of species, variability and evolution, fish distribution (bipolarity, amphiboreality, theory of faunal complexes), theory of development (developmental stages, etc.) and migrations, population dynamics, and others. These generalizations are also important for the development of bionics (mainly biohydroacoustics) and for some other problems.

The main sections of ichthyology are the same as those of zoology: systematics, phylogenetics, anatomy, physiology, ecology, biogeography, but the subject of their application is in this case specifically roundworms and fish. Traditionally, a significant place in ichthyology is occupied by the study of commercial species of roundworms and fish, including for the purpose of their artificial breeding.