Hello! I did a quick experiment after reading an article about swarming behavior in Wired Magazine.
Ever since I started working on fish mechanics I have become obsessed with swarming behaviors. 
A fish will swim until it bumps into another fish. When it does, it begins to match the other fish’s rotation.
If it gets too close it will rotate away from that fish.
A fish will follow the other fish until it bumps into another fish and then the behavior is repeated.
According to the article, if you shine a light, the fish will speed up until they are in shadow (safety).
They DON’T move away from the light source because apparently they are not aware of it.
The Experiment:
http://www.jupitermoon.com/music/swarm.html
The Article:
http://www.wired.com/wiredscience/2013/03/powers-of-swarms/all/
C