Rapid turning and swimming contribute to ecologically important behaviors in fishes such as predator avoidance, prey capture, mating, and the navigation of complex environments. For riverine species, such as knifefishes, that are commonly challenged by turbulent flows, turning control may be effective for counteracting adverse locomotive perturbations. Most research on fish maneuvering focuses on fish with traditional fin and body morphologies, which primarily use body bending and the pectoral fins during turning. However, it is uncertain how fishes with uncommon morphologies, are able to achieve sudden and controllable turns. Here we studied the turning performance and the turning hydrodynamics of the Black ghost knifefish (Apteronotus albifrons, N=6) which has an atypical elongated ribbon fin. Fish were filmed while swimming forward at ~2 BL s-1 and feeding from a fixed feeder (control) and an oscillating feeder (75 Hz) at two different amplitudes. 3D kinematic analysis of the body revealed the highest pitch angles and lowest body bending coefficients occurred during steady swimming. Low pitch angle, high maximum yaw angles and large body bending coefficients were characteristic of small and large turns. Asynchrony in pectoral fin use was low during turning, however ribbon fin wavelength, frequency, and wave speed were greatest during large turns.  Digital particle image velocimetry (DPIV) showed larger counter-rotating vortex pairs produced during turning by the ribbon-fin in comparison to vortices rotating in the same direction during steady swimming. Our results highlight the ribbon fin’s role in controlled rapid turning through modulation of wavelength, frequency, and wave speed.

This dataset was collected using 3D highspeed videography filming at 250 frames per second in the lateral and ventral views. Data analyzed using Matlab and R. 

IndividualxTreatment_HawkinsJimenezSanford_2021.xlsx [Data set used for statistical analysis including the means of each fish (N=6) per each treatment.]

AllObservations_HawkinsJimenezSanford_2021.xlsx [Data set with compiled means from each digitization sequence for each treatment for each fish (N=6)].

RawDataSet_fishxtreatment_HawkinsJimenezSanford_2021.xlsx [Data set with all calibrated digitization coordinates in the x, y, and z planes for each analyzed sequence. Small turn files can be found in sheets 1- 43, large turn files can be found in sheets 44-80, and steady swimming files can be found in sheets 81- 118. Point 1 (tip of snout], Point 2 (end of head), Point 3 (body point in between pectoral fins), Point 4 (body point), Point 5 (body point), Point 6 (caudal peduncle), Point 7 (tip caudal fin), Point 8 (left pectoral fin tip), Point 9 (left pectoral fin base), Point 10 (right pectoral fin tip), Point 11 (right pectoral fin base), Point 12 (ribbon fin tip), Point 13 (ribbon fin base corresponding to Point 12), Point 14 (ribbon fin tip of a contiguous wave).]