Experimentally testing the function of anal fins in the bluefin killifish, <scp> <i>Lucania goodei</i> </scp>

Anal fins are thought to affect many functions, including swimming, sperm flow and signalling. However, there are few experimental demonstrations of these functions. We manipulated male anal fins by placing a cut in the fin. We found that cut males had lower fertilization rates than uncut males. Females were less likely to be courted and guarded by cut than uncut males. Uncut males were more likely to dominate in male/male competition. Our study suggests that anal fins have multiple important functions for fertilization and reproduction.