Meeting Abstract
Eel-like locomotion is generally regarded as a metabolically efficient mode of swimming due to the low cost of transportation (COT) observed during steady swimming. Key to this efficiency is the ability to exploit pressure gradients that passively generate sub ambient pressure fields that enhance forward thrust along most of the length of the body. However, a major drawback of anguilliform locomotion is its inability to perform as adequately at velocities greater than 1 body length per second (BL s-1). This suggests that in addition to physio-morphological constraints the mechanical limitations of this mode of locomotion are driven by complex animal-fluid interactions. We assess the relative contribution of both reactive and sub-ambient suction forces at different speeds to identify the limiting factors of eel-like locomotion. Measurements of metabolic activity, swimming kinematics and non-invasive pressure fields were made for steady swimming coral catfish (Plotosus lineatus). High-speed, high-resolution particle image velocimetry (PIV) and respirometry data was collected using a modified 5L Brett-type swim tunnel. They revealed the influence of distinct body kinematics on the formation of flow structures along the body that result in a low COT at speeds of 0.5-1.0 BL s-1 and higher COT at velocities outside this range. During efficient swimming, two protovortices are always present and retained along the body at a given moment and may allow suction forces to dominate over reactive forces. Although such flow structures were also observed at higher swimming speeds, increased anterior lateral displacement of the body and posterior lateral velocity may result in the presence of dominant reactive forces. These lateral losses in kinetic energy may eventually result in no net acceleration of the fish and thus render anguilliform locomotion impractical.
