What do the fish in its environment?

Please provide me with more context! I need to know what "it" refers to in order to tell you what the fish in its environment do.

For example, you could ask:

* "What do the fish in a coral reef do?"

* "What do the fish in a river do?"

* "What do the fish in a tropical rainforest do?"

Once you tell me what "it" is, I can tell you about the fish in its environment!