The Cetus Coin, a single Constellation Coin out of the one hundred that can be collected in Endless Ocean: Blue World, is one of the six needed to complete the Voice of the Night Sky quest "The Hero Perseus". It can be found in the Gatama Atoll area, near Blue Cliff at coordinates A-7. In this shine spot, there are several small fish making their homes: a pair of Singular Bannerfish and a single Bluelashed Butterflyfish.