To answer your question, I need to know what kind of fish you're asking about.
For example, if you're interested in:
* Black sea bass: They eat shrimp, crabs, squid, and other smaller fish.
* Black carp: They are omnivores and eat algae, plants, insects, and small fish.
* Blacktip shark: They eat smaller fish, crustaceans, and cephalopods.
Tell me more about the fish you're interested in and I can give you a more specific answer about their diet!