Do sticklebacks cooperate repeatedly in reciprocal pairs?

Summary In a shoal of four sticklebacks (Gasterosteus aculeatus) individual fish had partners with whom they repeatedly performed pairwise predator inspection visits. In six different trials, we found two reciprocal pairs per trial significantly more often than would be expected by chance. These results provide further evidence for a TIT FOR TAT like cooperation strategy in sticklebacks. Offprint requests to: M. Milinski