Laboratory-bred juvenile three-spined sticklebacks from II sibships did not prefer to shoal with their siblings when they were offered the choice between odor from unfamiliar siblings and non-kin in a fluviarium, although the power for finding a significant preference was very high (0.99). The test fish preferred the side where odor from the heavier shoal was supplied; this shows that they could appreciate odor cues from conspecifics in our apparatus and should have preferred their siblings if such a preference exists. Our results are compatible with theoretical predictions but are at variance with previous findings by other authors. We used independent replicates in a blind protocol with strict randomization of fish and procedures.