system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How come in aquariums the predators don’t gobble up the prey? Are they trained not to do so?
gpt
Many fish will only attack when they are hungry, or won't attack fish they the don't recognize as food.

A good aquarium will be curated to take both these into account, and will only contain well fed, mutually compatible species.