Ah, the fish has three states. Wander, attracted, and flee. When you use the screech they enter the flee state. For a couple of seconds they run away from the ship (due to just having been scared). A fish won't enter the attracted state if its fleeing, causing it to not return.
I realize I should've added something similar for the monster, because the monster can return as soon as it hears a couple of sounds. This can be quite confusing and causes the monster to be a bit clingy.