By Susan Milius
Failing to get an expected snack rouses fish to fight with extra ferocity. The change in behavior is especially marked in undersized fish facing a big, scary opponent.
The fish version of frustration can drive little fish to posture at and fight big fish that they would normally flee from, says Marco Vindas of the University of Oslo. Two of 11 of these overheated David-and-Goliath matchups ended with the little fish unexpectedly trouncing the big one.