Fish fills in the gaps about unknown rivals
“Pick your battles wisely” is sound advice that people forget all too often. We could learn a thing or two from Astatotilapia burtoni, a little cichlid fish from the shallows of Lake Tanganyika in central Africa.
New research shows that A. burtoni possesses surprising powers of logic—for a fish. The males can deduce the pecking order among their rivals after watching only some of them fight each other.
Logan Grosenick and his adviser, Russell D. Fernald, a biologist at Stanford University, along with a colleague, placed “bystander” fish in the central part of an experimental tank. There the bystanders could watch staged, one-on-one fights between five rival males in compartments around the tank’s perimeter. To establish a dominance hierarchy among the rivals, the investigators predetermined the outcome of each fight by handicapping one contender—removing it from the water to stress it, then placing it in the other’s home tank. Only closely ranked rivals were pitted against one another. Thus the bystanders watched fish A fight and beat fish B, B fight and beat C, and so on through fish E.
After exposing eight bystanders to either two or four of the fights each day for eleven days, the investigators tested whether the bystanders had been able to infer the complete hierarchy despite the gaps in their knowledge. Each bystander was shown two males that had never fought—A and E or B and D—in compartments on opposite sides of the tank. In nearly all the trials, the bystander clearly identified the lower ranking of the two males, visiting him first and spending longer near him (a sensible preference, considering a bystander’s improved odds at beating a low-ranking rival). That cognitive leap is roughly equivalent to the reasoning abilities children attain around age four. Not bad for a fish!