In-Situ Observations of a Deep-sea Ceratioid Anglerfish of the Genus Oneirodes (Lophiiformes: Oneirodidae)
On 6 June 2005, the ROV Tiburon of the Monterey Bay Aquarium Research Institute captured approximately 24.4 min of footage (30 frames s−1) of a female ceratioid anglerfish, identified as a member of the genus Oneirodes, off the coast of Monterey, CA, at a depth of 1474 m. To gain insight into ceratioid behavioral ecology, this sequence was digitized and analyzed frame-by-frame. All relevant behaviors were described and the kinematics of one slow-swimming and one directional change sequence were quantified. These sequences captured both reduced (slow-swimming) and prominent (directional change) functions of the pectoral fins in producing motion. The angler was initially sighted passively drifting with its illicium extended. It swam away rapidly when approached by the ROV, but for most of the time, it remained lethargic, drifting with no preferred body orientation. When progressing, however, the fish swam slowly and intermittently at approximately 0.24 body lengths s−1, with its pectoral fins beating in-phase. Overall, the observed behaviors of Oneirodes support the hypothesis that these animals are lethargic, lie-and-wait predators, well adapted to the low energy conditions of deep-sea environments.Abstract
Oneirodes eschrichtii, LACM 31100-1, 71 mm standard length, type species of the genus Oneirodes Lütken. After Pietsch, 1974.
Frames of in-situ video of Oneirodes sp. used for kinematical analyses (light appearing to emanate from the esca and unpigmented tips of fin rays is reflection from lights of the ROV): (A) Initial sighting with illicium fully extended; (B) Passive drifting with body and extended fins immobile; (C) Anglerfish in dorsal view, showing points tracked in kinematical analyses: A = anteriormost margin of upper jaw; Bl and Br = base of left and right pectoral fin, respectively; C = distal tip of longest observable caudal-fin ray; H = posteriormost margin of hypural plate; Pl and Pr = distal tips of left and right pectoral-fin rays, respectively; (D) Initial fast-start escape response that marked the beginning of each burst swim. Courtesy of Bruce Robison and the Monterey Bay Aquarium Research Institute.
Selected kinematical results (translation as a function of time) from slow-swimming sequences of Oneirodes sp.: (A) Vertical translation expressed in body lengths (the slope indicates the velocity of the anglerfish); (B) Change in body vector angle expressed in radians; (C) Change in caudal-fin vector angle expressed in radians.
Vector angles of left pectoral fin of Oneirodes sp. (shown in dorsal view), recorded during a slow-swimming sequence (plotted as a function of time), showing in-phase pectoral-fin oscillation. Courtesy of Bruce Robison and the Monterey Bay Aquarium Research Institute.
Contributor Notes
Associate Editor: J. W. Snodgrass.