He is a dark purple fish with a lavender dorsal fin and lavender eyelids. He wears a navy blue suit over his body, and he has a white undershirt and a blue tie. He also has black shoes. He is usually seen with his clipboard. Starting in "Mall Girl Pearl," he has been seen with a blue dorsal fin, a brown hat, and a red tie.
Yellowtail appears as the health inspector for the Krusty Krab. Mr. Krabs and SpongeBob give him plenty of food. When he is done, he requests a regular Krabby Patty. Mr. Krabs and SpongeBob hear a news report that a fake inspector has been going around getting free food. Mr. Krabs assumed that Inspector Yellowtail was the Fake Health Inspector and he forces SpongeBob to help him make the worst patty possible; SpongeBob calls it the "Nasty Patty."
SpongeBob delivers it to Inspector Yellowtail. He is about to eat it when a fly gets in his throat and he chokes. He drops the patty and slips, knocking him out. Mr. Krabs and SpongeBob laugh at his pain, not seeing what happened.
Another news report comes in saying that the fake inspector has been caught. SpongeBob says that when they explain the situation to Inspector Yellowtail, they will all have a good laugh. Mr. Krabs looks out and says that he will not be laughing because the patty killed him.
Panicking, Mr. Krabs and SpongeBob take the body to the graveyard and try to bury the body. They walk away and Officer Nancy O'Malley and Officer John Slugfish drive by. They offer to drive Mr. Krabs and SpongeBob to the Krusty Krab. They take the offer and go back to put the shovel in the trunk. It starts to rain and Inspector Yellowtail's body slides down the mud and SpongeBob notices. They put the body in the trunk and get into the police car as the car drives away.
Using code, Mr. Krabs tells SpongeBob to take the body and put it into the freezer. When they get back to the Krusty Krab, SpongeBob tries to go through the backdoor, but it is locked. He then puts the body in his hat and goes through the front door. Later, Officer Nancy requests ice in her drink, and the two try to hide what they have done. Eventually, they have to open the freezer door and the body is not there. Jokingly, they think that Inspector Yellowtail became a zombie. Inspector Yellowtail shows up and they all think that he is a zombie. Officer Nancy and John hit him with heavy objects and Officer John notices that he is not a zombie, revealing to SpongeBob and Mr. Krabs that he is alive. Inspector Yellowtail then gives the Krusty Krab a passing grade.
After Mr. Krabs says that everyone will get patties, Yellowtail is happy to eat one before he is hit in the face though presumably eats.
He is seen in the "Nasty Patty" segment of the book.
"The Krabby Kronicle"
Plankton assumes he has created the "Chumstick that will finally run Mr. Krabs out of business." However, Inspector Yellowtail shows up and closes the Chum Bucket down after reading the Krabby Kronicle article that says "Plankton's Chum Made of Your Chums!!!" Later in the episode, Plankton claims that due to Mr. Krabs' lying actions, he lost the Chum Bucket. Furthermore, it is the episode where Yellowtail's last name is revealed.
"Mall Girl Pearl"
He makes a cameo appearance at the mall when Pearl is going down an escalator.
Inspector Yellowtail is called by Squidward to close SpongeBob's Place about halfway through the episode. He and Carl appear at the end, shutting it down, because it is against state law to sell food inside a pineapple. In this episode, his first name is revealed and it is known that he is a boss to Carl, a rookie health inspector.