Arnold is a The Angler Fish who apparently lives in Rock Bottom and appears in the episode other residents of Rock Bottom appeared in, he doesn't talk with a tongue accent. Although, he is heard blowing raspberries with his tongue. But in the end, when Spongebob tries to thank him while blowing raspberries, he responds by saying, "You're welcome!" without the accent.
He is dark red and has a "stalk" on his head with a red orb on the top, which glows. He wears a purple bow tie. He has three dark red spots on both sides of his head, he has a pink fin, he has red eyes, and he has large dark purple lips, with a normal pink tongue. He looks much more normal in comparison with the other Rock Bottomites.
After getting off the bus, he helped SpongeBob by chasing after his glove balloon and returning it to him. After which he inflated SpongeBob's balloon to float back to Bikini Bottom. SpongeBob said "Thank you!" in the tongue accent, but the Angler Fish responded by saying "You're welcome!" in a normal accent, much to the surprise of SpongeBob.
This might be because he travels outside of Rock Bottom frequently. His knowledge and quick thinking of Spongebob's escape method may suggest that the angler fish from Rock Bottom has used this escape/getaway method before.