Green, M.H., Ho, R.K., and Hale, M.E. (2011) Movement and function of the pectoral fins of the larval zebrafish (Danio rerio) during slow swimming. The Journal of experimental biology. 214(18):3111-3123.
Pectoral fins are known to play important roles in swimming for many adult fish; however, their functions in fish larvae are
unclear. We examined routine pectoral fin movement during rhythmic forward swimming and used genetic ablation to test hypotheses
of fin function in larval zebrafish. Fins were active throughout bouts of slow swimming. Initiation was characterized by asymmetric
fin abduction that transitioned to alternating rhythmic movement with first fin adduction. During subsequent swimming, fin
beat amplitude decreased while tail beat amplitude increased over swimming speeds ranging from 1.47 to 4.56 body lengths per
second. There was no change in fin or tail beat frequency with speed (means ± s.d.: 28.2±3.5 and 29.6±1.9 Hz, respectively).
To examine potential roles of the pectoral fins in swimming, we compared the kinematics of finless larvae generated with a
morpholino knockdown of the gene fgf24 to those of normal fish. Pectoral fins were not required for initiation nor did they significantly impact forward rhythmic
swimming. We investigated an alternative hypothesis that the fins function in respiration. Dye visualization demonstrated
that pectoral fin beats bring distant fluid toward the body and move it caudally behind the fins, disrupting the boundary
layer along the body's surface, a major site of oxygen absorption in larvae. Larval zebrafish also demonstrated more fin beating
in low oxygen conditions. Our data reject the hypothesis that the pectoral fins of larval zebrafish have a locomotor function
during slow, forward locomotion, but are consistent with the hypothesis that the fins have a respiratory function.