Eli5 – how do fish distinguish between non threatening fish/sealife and predators

Question

Context and example – just watched a video of a turtle entering a pond full of fish for the first time and they were all super chill

In: 19

Answer 1

There are fish that avoid predators, and the ones who don’t.

The ones who avoid them pass on their genes, which make baby fishes that avoid predators

Answer 2

Fish are sensitive to movement. Predators tend to move quickly and directly toward prey. Whereas non-predators . . . don’t. Fish will move out of the way when movement suggests imminent danger.