Macrouridae, Bonaparte, 1831

3.2 | Macrouridae View in CoL : C. yaquinae

Four examples of backward swimming by C. yaquinae were observed. At deployment 5 (Figure 3) the nose of the fish was above the camera, and it swam backward for five tail beats, presenting a view of its ventral surface to the camera as it moved away into the center of the field of view (Video S5). The pectoral fins executed a backward paddling motion, where the left and right fins were 180 out of phase with one another but in synchrony with tail beats (Figure 3). In contrast to the eel I. robinsae the head did not oscillate from side to side; in Figure 3, the tip of the nose follows the line marking the straight track between the start and end positions. After the backward escape maneuver, the fish turned to its right by bending the body in an arc and aided by a power stroke of the left pectoral fin continued swimming forward away from the lander.

At deployment 6, the fish was below the camera and moved backward using both reverse body undulations and pectoral-fin motions, presenting its dorsal surface to the camera. Having completed the move away from the camera, it then began forward swimming toward the camera but used its pectoral fins as hydroplanes to ascend and pass safely above the camera (Video S6). At deployment 7, the fish was trapped, upside down on the sediment beneath the bait retaining bars of the lander. It extricated itself by backward swimming with combined reverse body undulations and pectoral-fin paddling at the sediment interface. It then righted itself by bending the body in a tight “C” shape and, aided by movement of the pectoral fins, turned and straightened its body to swim forward away from the lander (Video S7). At deployment 8, the fish was observed moving slowly backward aided by the bottom current passing waves along its body and paddling with the pectoral fins. After this backward excursion, it began swimming forward against the current (Video S8). In all four cases, the macrourid used a reversed propulsive wave of the body and tail together with alternating paddling motions of the pectoral fins to swim backward away from the lander.