It seems like not a day goes by without a new study demonstrating fish have more on the ball than anyone ever thought. Last week, we learned that fish can do math. In this latest study, researchers at Stanford University demonstrated that a species of Cichlids (from same family as Oscars - like Snow and Ice), were able to perform transitive inference.
The researchers said this type of logical reasoning is a developmental milestone for human children, showing up nonverbally as early as ages 4 and 5; it also has been reported in monkeys, rats and birds. It is the kind of thinking that allows people (and animals) to reason that if A is bigger than B, and B is bigger than C, then A is also bigger than C.
This is another example where a fish's ability to learn, in this case, about the dominance hierarchy of other fish in its evironment, would provide significant survival advantage.