DOI: 10.5061/dryad.sqv9s4n37
title: Beyond the Karman Gait: Knifefish swimming in periodic and irregular vortex streets

description: Neotropical freshwater fishes such as knifefishes are commonly faced with
 navigating intense and highly unsteady streams. However, our knowledge on
 locomotion in apteronotids comes from laminar flows, where the ribbon fin
 dominates over pectoral fins or body bending. Here, we studied the 3D
 kinematics and swimming control of seven black ghost knifefish
 (Apteronotus albifrons) moving in laminar flows (flow speed
 U&[infin] ~ 1 &[minus] 5 Bl/s) and in periodic vortex
 streets (U&[infin] ~ 2 &[minus] 4 Bl/s). Two different
 cylinders (~2 and ~3 cm diameter) were used to generate the latter.
 Additionally, fish were exposed to an irregular wake produced by a free
 oscillating cylinder (~2 cm diameter; U&[infin] ~ 2 Bl/s). In
 laminar flows knifefish mainly used their ribbon fin, with wave frequency,
 speed and acceleration increasing with U&[infin]. In contrast,
 knifefish swimming behind a fixed cylinder increased the use of pectoral
 fins and resulted in changes in body orientation that mimicked steady
 backward swimming. Meanwhile, individuals behind the oscillating cylinder
 presented a combination of body bending, ribbon and pectoral fins
 movements that counteract the out-of-phase yaw oscillations induced by the
 irregular shedding of vortices. We corroborated passive out-of-phase
 oscillations by placing a printed knifefish model just downstream of the
 moving cylinder but, when placed one-cylinder diameter downstream, the
 model oscillated in phase. Thus, the wake left behind an oscillating body
 is more challenging than a periodic vortex shedding for an animal located
 downstream, which may have consequences on inter- and intra-specific
 interactions.
description: VideoS1.mp4 [(00:05 s) Knifefish swimming in laminar conditions. (00:16 s) Fish swimming behind a large and small fixed cylinders. (00:36 s) Fish swimming in laminar, behind the small fixed cylinder and behind the oscillating cylinder. (01:15s) Fish showing passive movements in the wake of an oscillating cylinder. (01:31 s) 3D printed fish model in both the wake of a fixed cylinder and the wake of an oscillating cylinder. (01:49 s) Instantaneous vorticity fields of the ribbon fin of a knifefish swimming in laminar conditions, behind the fixed cylinder and behind the oscillating cylinder]. DataSet_OrtegaJimenezSandfordKnifefish.xls [Datasets for each fish (N=7) including all kinematic variables used for statistical analysis] RawData_OrtegaJimenezSandfordKnifefish..xlsx [3D digitized points in Cartesian system XYZ in cm of seven ghost knifefish swimming in laminar and unsteady flow conditions. Point 1 (head), Point 2 (tail tip), Point 3 (Left-pectoral fin tip), Point 4 (Right-pectoral fin tip), Point 5 (Left-pectoral fin base), Point 6 (Right-pectoralfin base), Point 7 (Ribbon fin tip at the midline), Point8 (trough tip formed by the ribbon fin wave), Point 9 (back-middle point), Point 10 (Ribbon fin base at the midline).Each fish (n=7) is order sequentially for each condition. LAMINAR CONDITIONS: -1.4 Bl/s (sheet 1to 7), 1.4 Bl/s (sheet 8 to14) 1.8 Bl/s (sheet 15 to 21), 2.5 Bl/s (sheet 22 to 28), 3 Bl/s (sheet 29 to 35), 3.6 Bl/s (sheet 36 to 42), 3.9 Bl/s(sheet 43 to 49), 4.3 Bl/s(sheet 50 to 55), and 4.6 Bl/s. (sheet56 to 57). SMALL CYLINDER CONDITIONS: 1.8 Bl/s (sheet 58 to 64), 2.5 Bl/s (sheet 65 to 71), 3 Bl/s (sheet 72 to 78 and 3.6 Bl/s (sheet 79 to 85). LARGE Cylinder Conditions: 1.8 Bl/s (sheet 86 to 92), 2.5 Bl/s (sheet 93 to 99). OSCILLATING CYLINDER CONDITION: 1.8 Bl/s (sheet 100 to 106). Digitalization software is described in: Hedrick, T. L. (2008). Software techniques for two- and three-dimensional kinematic measurements of biological and biomimetic systems. Bioinspir. Biomim. 3, 034001].