To provide a feed additive microorganism and a feeding method constituting the principal parts of the technology for proceeding an organic fish culture of 'sustainable environment protection-type fish culture' to breed healthy fish free from fish disease and keep the safety and health of the people.

Microorganisms included in activated carbon to improve the sustainability are mixed in combination with a solid feed to a starch solution such as brown alga glue or a food additive CMC before feeding and the mixture is supplied as a feed to promote the health of fish body and clean the water quality. In the case of feeding the fish with moist pellet, the microorganisms are mixed with minced fish meat and fine powder of shell. The feeding process is effective for inhibiting the growth of harmful microorganisms in the intestine of fish to prevent the fish disease, improve the balance of intestinal bacteria and add minerals and, in addition to the above, to satisfy the condition necessary for keeping the ecosystem by the action of microorganisms settled in the activated carbon in the discharged feces of the fish.