Might be able to do this with the pin behaviour. Set one fish to be the leader, then have the others pinned to that leader, offset at different random x/y to give the impression they're bunched up.
Yes I have thought of doing this, but I kind of wanted more "freedom" for fish, in my case, to move around. The fish are moving around randomly seemingly swimming as a group, but weaving between each other.
Thank you for the reply!
blackhornet Thanks for the response, but I am using C3, so I am not sure if that would work. If it does...