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Fuel-free magnetically driven propulsion of flexible Au/Ag/Ni nanowires, with a gold 'head' and nickel 'tail', linked by a partially dissolved and weakened silver bridge, is described. The flexible bridge facilitates the cyclic mechanical deformations under an external rotating magnetic field. Under such a field the nickel segment starts to rotate, facilitating the rotation of the gold segment at a different amplitude, hence breaking the system symmetry and inducing the movement. Forward ('pushing') and backward ('pulling') magnetically powered locomotion and a precise On/Off motion control are achieved by tailoring the length of the nickel and gold segments and modulating the magnetic field, respectively. Efficient locomotion in urine samples and in high-salt media is illustrated. The new magnetic nanowire swimmers can be prepared in large scale using a simple template electrodeposition protocol and offer considerable promise for diverse practical applications.

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Routine activities of early life history stages of fishes occur in an intermediate hydrodynamic environment (as identified by Reynolds numbers), between a zone where drag is linearly dependent on velocity and resistive forces make large contributions to thrust, and a zone where inertial forces dominate except in the boundary layer immediately adjacent to the body surface. Sprint performance carries larvae into this latter zone; thus, locomotor activities important for survival of both larvae and adults occur in the same hydrodynamic environment and similar selective pressures would be expected to influence locomotor morphology of larvae and adults. The simplest framework for evaluating and interpreting development of larvae recognizes the parental form as the developmental terminus and uses adult forms as references to identify similarities and discrepancies in larva structure. Three measures of locomotor structure are used to examine changes during development: (a) the ratio of caudal peduncle depth to maximum body depth, which is small in thunniform fish; (b) a body shape factor, which is small in chaetodontiform fishes; and (c) a transient swimming thrust factor, which is large in esociform fish. Similarities in form are found in yolk‐bearing larvae and are attributed to oxygen demand. Similarities in the pattern of development of larvae directly towards the parental form are found for fusiform species, except for delayed development of the caudal fin in tunas that probably is due to the hydrodynamic regime of the tail. Convergence with parents does not occur during the larva stage of deep‐bodied, compressed species. This is attributed to high drag of compressed forms at low Reynolds numbers and diet differences between larvae and parents. Although this framework is successful in identifying and interpreting problems, comparative studies of form, kinematics, and performance during biologically important activities are essential.

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A kinematic analysis of optimal avoidance and evasion techniques for prey is presented. The analysis is mainly directed towards piscivorous interactions but can include other aquatic and terrestrial cases. Avoidance is defined as maneuvering for position by prey, before the predator starts a chase, while evasion is an escape response to an attack.Two separate optimal avoidance methods are found and analyzedminimizing time within sighting range; and maximizing instantaneous distance. The second method leads to the well-known "fountain effect" of fish school break-up when predators are in the vicinity.The optimal evasion technique involves escape at a small angle (up to 20") from the heading directly away from the predator. This is in agreement with observations of escaping minnows.

The dictionary definition of stability as "Firmly established, not easily to be changed" immediately indicates the conflict between stability and maneuverability in aquatic locomotion. The present paper addresses several issues resulting from these opposing requirements. Classical stability theory for bodies moving in fluids is based on developments in submarine and airship motions. These have lateral symmetry, in common with most animals. This enables the separation of the equations of motion into two sets of 3 each. The vertical (longitudinal) set, which includes motions in the axial (surge), normal (heave) and pitching directions, can thus be separated from the lateral-horizontal plane which includes yaw, roll and sideslip motions. This has been found useful in the past for longitudinal stability studies based on coasting configurations but is not applicable to the analysis of turning, fast starts and vigorous swimming, where the lateral symmetry of the fish body is broken by bending motions. The present paper will also examine some of the aspects of the stability vs. maneuverability tradeoff for these asymmetric motions. An analysis of the conditions under which the separation of equations of motions into vertical and horizontal planes is justified, and a definition of the equations to be used in cases where this separation is not accurate enough is presented.

The hydrodynamic forces due to the motion of a flexible foil in a large amplitude curved path in an inviscid incompressible flow are analysed. A parametric study of large amplitude oscillatory propulsion, with special emphasis on the effect of chordwise flexibility of the fin, is presented. This flexibility was found to increase the propulsive efficiency by up to 2% while causing small decreases in the overall thrust, compared with similar motion with rigid foils.