The Prehistoric Purple Fish is seen in the beginning of the episode "Ugh."
The Prehistoric Purple Fish, like the name says, is mainly purple in color. Its body highly resembles that of a whale. It has large light blue stegosaurus-like scales on its back and very short fins. It also has two small eyes with thick eyebrows. A few razor-sharp light yellow teeth can be seen jutting out of the lower jaw of its wide mouth. The top of its head consists of a blowhole and at least three hair-like growths. Its skin is detailed with scales.
The Prehistoric Purple Fish is first seen in the very beginning of the episode "Ugh." It makes a noise which sounds similar to SpongeBob's alarm clock. It may act as SpongeGar's alarm clock every morning.
The Prehistoric Purple Fish appears to be the early ancestor of a whale.
The Prehistoric Purple Fish's purpose is similar to SpongeBob's alarm clock, to wake up SpongeBob and SpongeGar.