Oh, I just saw the project on your profile @spacer. And here's what I think I could code to make the AI fishes.
There will be a random integer selecter. This random integer decides whether the fish wants to get eaten and deal with the deathly consequences or whether the fish wants to run away and NOT get eaten.
Then, the fish would stay at it's X Position and wait until you catch it, or it will shift it's X Position if it is in your X Position. Sounds good?
Oh yeah, I saw your project on an online server using Cloud Variable blocks. I'm making a classroom software, kind of like Google Classroom, in Snap! and I am currently using Browser Data. But are cloud variables better for online or Browser Data?