What does a fish do if you hold mirror in front of it?

A fish will initially be curious about the mirror and try to explore it. The fish may see the reflection in the mirror and believe it is another fish. It might attempt to interact with the reflection by swimming toward it, flaring its fins, or displaying other aggressive or friendly behaviors. However, over time, the fish will likely realize that the reflection in the mirror is just its own reflection, and it may eventually ignore the mirror or start using it to check its appearance.