It was either "A Fish Called Wanda" or "My Pet 'alibut Eric".
Customer: Hello, I would like to buy a fish license, please.
Shopkeeper: A what?
C: A license for my pet fish, Eric.
S: How did you know my name was Eric?
C: No no no, my fish's name is Eric, Eric the fish. He's an halibut.
S: What?
C: He is...an...halibut.
S: You've got a pet halibut?
C: Yes. I chose him out of thousands. I didn't like the others, they were all too flat.
S: You must be a looney.