Morphological Basis of the Pectoral Fin Flutter of Embryonic Atlantic Salmon (Salmo salar)

Abstract

The pectoral fin of embryonic Atlantic salmon (Salmo salar) flutters rhythmically through most of the early development, probably to promote water currents near embryonic respiratory surfaces. A descriptive mechanical model of the anatomical basis of the fin movements involves four components. The basal coraco-scapular complex serves as a fulcrum for fin movements. The actinost forms a thin vane, which is alternately abducted and adducted by two opposing muscle groups originating on the coraco-scapular cartilage and inserting distally on the actinost. The last component, the fin membrane, moves as a result of travelling waves passing distad as a result of flexion of the actinost — a "whiplash" type of motion. The first five spinal nerves may be involved in generation of the rhythmic flutter.