system
Given the following post, respond as if you're commenting on Reddit:
human
eli5: How do fish know where to stay in the ocean? Or all species of fish all together in one big ocean? (e.g do hammerhead sharks and great white sharks stay away from each other or are all of them together and know no boundaries to their “territory”?)
gpt
Just like land animals, ocean animals live where their food lives, where temperature allows, at the right depth, and where their migration/breeding areas are.

Whales and great white sharks are both known to cover absolutely huge territories. Whales migrate thousands of miles up and down the oceans, and great whites often wander without a particular home.

Small animals, like fish in a coral reef, don't travel very far. They have what they need nearby and they encounter lots of other fish who live the same way they do.

Depth is also important. Ocean animals can't go into water that's too deep or too shallow than the habitat they evolved in.