Fig. 8. Posterior view of one needlefish swimming steadily at three speeds, showing the position of the various fins. When the fins are not obstructed from view, arrows are used to denote their location. Solid arrows point to the pectoral fins, hollow arrows point to the tips of the dorsal and anal fins, and double-headed arrows point to the trailing edge of caudal fin. Scale bar, 1 cm. (A) At the lowest speed, the pectoral fins are clearly seen in the horizontal plane during mid-abduction. The dorsal fin is angled to the left of the body while the anal fin is obscured by the caudal fin, which is vertical and held in line with the body axis. (B) At intermediate speeds, the pectoral fins are held away from the body. The dorsal and anal fins are offset from the body midline, and the caudal fin adopts a W shape as it completes a beat to the left. (C) At the highest sustainable speed, the pectoral fins are held flush against the body and the W shape of the caudal fin becomes more exaggerated (see text for a description). From this view, the lateral excursion of the dorsal and anal fin is not clear, but as the tail beats to the left the flexible median fins lag towards the right of the fish. Note that the height of the median fins is not as great as in B.

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