To avoid enemies or move slower as to not cause suspicionI'm sure the game can make one, I don't know if there's an incentive for them to do it, why would the fish want to go backwards ?
I mean, that would require 2 things, first something for fishes to be able to hide behind things like seaweed, I'm not sure if it's not already here, and the second thing that would require would be something for predators to sense a prey even if it's hidden, like the movement of water they cause when movingTo avoid enemies or move slower as to not cause suspicion