What's a fish's favorite genre of music?

This joke swims in the delightful waters of wordplay, specifically a pun. The humor hinges on two completely different meanings of the word "scales." In music, a scale refers to a series of notes arranged by pitch, forming the building blocks of melodies. For our aquatic friends (Review), however, scales are the protective, overlapping plates that cover most fish, shielding them from the outside world. The unexpected twist comes from applying the musical term to a fish's physical attributes.

Adding another layer to this comedic catch is the phrase "heavy metal." In the world of music, heavy metal is a genre born in the late 1960s and early 1970s, known for its loud, distorted guitars and powerful beats. Bands like Black Sabbath and Led Zeppelin were pioneers, creating a sound often described as "heavy." When paired with "scales," the joke cleverly conjures an image of fish with tough, metallic-looking scales, perhaps even headbanging to their favorite aquatic tunes. Some fish, like gars or sturgeons, actually have ganoid scales that are thick and diamond-shaped, forming a hard, armor-like shell, which could be considered "heavy" in a literal sense.

So, the joke works by reeling in the listener with the familiar concept of musical genres, only to deliver an amusing bait (Review)-and-switch with the unexpected, literal interpretation of a fish's protective covering and the "heavy" nature of some of those natural defenses. It's a classic example of a pun that makes you groan and grin at the same time.