Make fish have a customisable swim distance (similar to NPC walk distance)

Fish in ponds get 'stuck' to the sides of small ponds rather than swim in the middle, and fish in aquaria end up swimming out of the side of water walls and on to the floor.
Why not make a distance they can swim, so they will be contained as they swim and not try to escape? Would help in smaller pools no end!
You can choose how far the NPCs can go, so why not fish, and other animals?