MORPHOLOGICAL BASIS OF THE PECTORAL FIN FLUTTER OF EMBRYONIC ATLANTIC SALMON (SALMO-SALAR)

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.