Locomotion of herring and plaice larvae

Abstract

The swimming of larval plaice Pleuronectes platessa L was recorded using silhouette cinematography and that of larval herring Clupea harengus L by television and video recorder. The swimming style of herring was found to change with growth. The amplitude of swimming movements of very young larvae increased linearly towards the tail, so that resistive rather than inertial forces were the more important. At a length of 20 mm when caudal and dorsal fins had developed, a new type of swimming was adopted in which amplitude increased more rapidly along the length of the body so indicating the greater importance of inertial forces. Plaice larvae used pectoral fins and body waves simultaneously at cruising speeds. The fins did not produce thrust but counteracted recoil and so prevented yaw of the head. This was achieved by synchronized tail and fin movements with a 180o phase difference between the strokes of each fin. Body wave speed: swimming speed ratio u/v was low increasing from 0.2-0.4 as the larvae swam faster. At burst speeds plaice larvae changed swimming style and used very high tail beat frequencies. The pectoral fins were not used and the length of the body wave lengthened. A new kinematic model, based on the angle between segments of the body and direction of motion, was fitted to a swimming herring larvae 22mm in length. This model demonstrated both variation in wavelength and speed of the propulsive wave within the tail bear cycle. The distribution of red and white muscle fibre types of larval herring changed during growth. On hatching, when the larva was dependent on cutaneous respiration, red muscle fibres were arranged as a single layer under the skin. The adult distribution with red muscle concentrated along the mid-flank developed after the gills and circulation became fully functional.