The book collection "Aquaponics systems, fish" is intended to disseminate the sciences of synergistic food production such as aquaponics. This food production system is accessible to the general public and eliminates many of the current problems related to food supply. In this third volume, the chapter referring to the interaction of fish in the aquaponic system will be mentioned, especially referring to specific issues of fish farming. The fifth chapter concludes the function of fish in the aquaponic system, the types of fish and the necessary conditions for their breeding, costs, benefits and characteristics. In the following volumes, the aspects of maintenance, automation systems and methods to improve productivity in the aquaponic system will be mentioned. The whole system of books called "Aquaponics systems" is divided into three texts which are "Aquaponics systems, plants", "Aquaponics systems, fish", "Aquaponics systems, microbes" and "Aquaponics systems, automation and intelligent control". The entire collection is intended to provide insight into advances in the science of aquaponics and food production in the 21st century. It is taken for granted that the implementation processes of aquaponics units will be mentioned, but new techniques and technologies for increasing production are also published.