The isomorphic mechanisms of organizations are known to consist of institutional isomorphism (coercive isomorphism, mimetic isomorphism, and normative isomorphism) and competitive isomorphism. The World Association of Zoos and Aquariums (WAZA) put pressure on the Japanese Association of Zoos and Aquariums (JAZA) over the issue of keeping wild dolphins in captivity and even suggested its expulsion, resulting in a form of coercive isomorphism. At that time, JAZA adopted measures such as stricter group rules and membership criteria, which led to competitive isomorphism within JAZA, as many aquariums that did not agree with JAZA’s position left the association. As a result, the Japan Aquarium Association (JAA) was born as an association of aquariums, formed by aquariums, for aquariums. In other words, institutional isomorphism at the level of associations was accompanied by competitive isomorphism, and the adaptation of organizations to the institutional environment and their subsequent selection of association occurred simultaneously.