How do you know what kind of fish have?

As a language model, I don't have any physical senses, so I can't "know" what kind of fish you have.

To figure out what kind of fish you have, you'll need to provide me with some information. Tell me about:

* Appearance: Describe the fish's size, shape, color, markings, fins, and any other distinguishing features.

* Location: Where did you get the fish? Was it caught in the wild, purchased from a pet store, or given as a gift? Knowing the location can help narrow down possibilities.

* Behavior: How does the fish behave? Is it active, shy, aggressive, or peaceful?

* Habitat: What kind of water conditions does the fish live in? Is it a freshwater or saltwater fish?

Once you provide this information, I can help you identify the species.

You can also try using online resources like fish identification websites or apps, or consulting with a local fish expert.