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.

Individual three-spined sticklebacks {Gasterosteus aculeatus) moved closer to a predatory trout when a "cooperator" stickleback, which the test fish could see through a one-way mirror, swam up to the predator than when a "defector" stickleback appeared to swim only half as close to the predator. After four training runs with both types of partners, the former cooperator. also defected. The test fish continued to move closer to the predator in the presence of the former cooperator even though both the former cooperator and the defector now appeared to stop in their approach to the predator at the same distance. This shows that probable partners build up trust.

No abstract