Nearly four-fifths of the 28,000 known species of fish swim in schools, harmoniously aligning their movements with others around them. Besides reducing drag for those not in the front of the pack, coming together makes it harder for a predator to single out just one prey; a mass change of direction by the entire school might act to confuse the attacker further.
That, at least, is the theory. The rub is that testing it requires manipulating the behaviour of real fish—trickier even than herding cats. Now, though, Christos Ioannou, from Bristol University, may have found a way around it. As the researchers report in Science, he and his colleagues have developed a video game for piscine predator to play.
They put their gamer, a hungry bluegill sunfish, into a tank and projected computer-generated prey on one of its walls. Each digital fish in the 16-strong school was programmed to maintain their speed and to move away to avoid collision if they get too close to each other. But each was also endowed with a mind of its own: some ignored what their neighbours did while others followed their every move.
It turns out that the real sunfish is indeed more likely to go after the lonely virtual minnows than the more gregarious ones. It seems, then, that there really is strength in numbers, though it be some time before Dr Ioannou manages to coax his bluegill into disclosing precisely why it prefers the loners.
Also published on economist.com.
Reference: Ioannou CC, Guttal V, & Couzin ID (2012). Predatory Fish Select for Coordinated Collective Motion in Virtual Prey. Science PMID: 22903520
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