Even though they are first seen in Blue Moon Bay, you'll have to complete a later level to be able to see the ones in Blue Moon Bay.
Mangobies are fish that are colored and shaped like a mango. They have two large eyeballs with maroon pupils. Their color is orange, yellow, and green (respectively from the head to the tail). They swim in every direction, and can be defeated only by those characters with the swim boost ability (Utah, Gremmie, and Nick).