Kinematics of the ribbon fin in hovering and swimming of the electric ghost knifefish

Abstract

Two errors appeared in J. Exp. Biol. 216, 823-834.During data processing, the wrong scaling factor was used when converting the fin amplitude from pixels on the video to linear displacement in millimetres [term y(x) in Eqn 1]. This error caused the angular displacement to be underestimated by a factor that varied between 2.9 and 3.6 (mean ± s.d. = 3.28 ± 0.27) for the different data sets.The error is found in Figs 2, 4, 9 and 10. In the right panels of Fig. 2, both panels of Fig. 4, Fig. 9C and the color bar in Fig. 10, the range of the y-axis is approximately three times smaller than it should have been.In the Results and Discussion, we comment on the direction of the change in amplitude at different swimming speeds. The error does not affect these comments because the amplitude at all swimming speeds was scaled by approximately the same factor.A second error was introduced when calculating the ratio of the fin length to the fin base length. The measurement of the fin base length was performed only on the first frame of every data set, instead of averaging the length across all the frames as was done for the fin length. This caused the ratio of fin length to fin base length to be larger in the hovering condition and smaller when swimming at 6 cm s−1. After the correction, the ratio is more constant than before.This error can be found in Fig. 9B, as well as in the sentence ‘The amount of stretch might not be insignificant: as Fig. 9B shows, the edge of the fin is 1.3 times the length of the fin base for a hovering fish.’ This sentence should read ‘The amount of stretch might not be insignificant: as Fig. 9B shows, the edge of the fin is 1.2 times the length of the fin base for a hovering fish.’The corrected figures appear here.The authors apologise for any inconvenience, and assure readers that these errors do not affect any other part of the analysis or conclusions.