Q: What’s the difference between a guitar and a fish?
A: You can’t tuna fish!

Explanation: Tuna fish?  No, tune – a – fish.  You see, for a guitar to sound good, you have to tune it.  A fish cannot be tuned… but there is a fish called a tuna fish.

This joke is funny because “tune a” sounds like “tuna.”

Here is a tuna fish video that is in tune and has a nice jingle at the end: