Singing fish are a type of novelty item that produce musical sounds when activated. These fish are often made of plastic and are designed to mimic the appearance of real fish. When a button is pressed or when they detect motion, they move their mouths and play a song, creating an entertaining display. The concept of singing fish became popular in the late 1990s, with products like the Big Mouth Billy Bass leading the trend. These items are often used as humorous decorations in homes or offices, appealing to those who enjoy quirky and fun collectibles.