After some time fish schools form. Organized group emerges from 3 rules: align, avoid, cohere (as in the famous "boids" model of flocking).
Background by Kathy (as the fractal coral model), whirl effect oscillating with sine function. I've shared several bird flocking models using more complex vector calculations. This one's adapted a bit for fish, making them turn around at edges as if they encounter glass of fish tank. Lone fish boids don't have much initiative of their own, but are only following others. In the early phases especially, the behavior seems disorganized, and lone fish can flip back and forth more than would be the case in reality. I looked at many other boids implementations. Based on Reynold's famous boids model of flocking.
