What is the three-ring theory of aquatic diseases?

The so-called three-ring theory of aquatic diseases, also known as the three-ring principle, refers to the interaction among fish, water environment and pathogenic microorganisms. When any two of these three factors exist at the same time, the fish will be in a sub-health state, and only when these three factors exist at the same time will fish diseases break out. As long as you control any link during the period, you can control fish diseases, such as improving water quality, improving fish physique or inhibiting the activity or quantity of pathogens. The schematic diagram is as follows: