Flounder

Flounder is the bright yellow and golden blue colored tropical fish and Ariel's best friend and the secondary tritagonist in The Little Mermaid series and movies.

The Little Mermaid: Ariel's Beginning
Flounder is seen as a yellow guppy with blue stripes. She is met by Ariel in the dangerous part of Atlantica. As King Triton banished music from the kingdom, he and Ariel are warned by the swordfish guards that they will be arrested. He then meets up with some fish playing music such as Catfish Club. Later, King Triton's guards arrested them and put them to prison. As an escape, he and Ariel are stopped by Marina's eels and Ariel hit Marina on a log. Flounder is later seen in the crowd after music is brought back to the kingdom.

The Little Mermaid
After the prequel, Flounder goes aside Ariel who is in the faraway outlands when trying to avoid Glut. He is later seen during Ariel's signature song, "Part of Your World". Later, the two go after Sebastian thinking why the human world is dangerous and must live under the sea. After that, Sebastian sings his signature song ("Under the Sea"). Flounder and Ariel feel sad after King Triton destroyed the statue of Prince Eric, meaning that humans and mermaids never get along. He and Ariel are later seen in Ursula's cave and during her song, "Poor Unfortunate Souls". As a human, Ariel meets Eric and then Flounder is seen on the marsh where Sebastian sings his second signature song, "Kiss the Girl". After that, Ursula sets a storm to attack Atlantica and Flounder is seen with the other aquatic animals during Ariel and Eric's wedding after the witch's death.

The Little Mermaid 2: Return to the Sea
Flounder, still a yellow fish, is no longer a guppy. Instead, he is seen as an adult fish with children. He serves a minor role when Melody is still a mermaid. He is protective of his children.