Whale

The Whale is the name given to the unknown fish portraying a large shadow seen in and  on a trip to the island. It is approximately 20 times the length of the average Sea Bass shadow and it cannot be caught.

A YouTube video exists showing footage of the massive shadow. If the player decided to try to catch it, rumours go that it's catchable but, when dropped, it takes the place of a beta fish icon. Although, as of now, it is uncatchable.