Fish physiology is considered as an integral part of the course "General physiology of humans and animals." The osmoregulation of fish, the activity of their kidneys and gills, sensory systems (vision, hearing, etc.) are described. Characteristics of the nervous system, skin, fish movement are given. Features of blood circulation, gas exchange, digestion are described. Attention is paid to the physiological foundations of artificial nutrition of fish, the physiology of their reproduction. Fish endocrine system, their immunity, behavior in various conditions, stress state, etc. are characterized.