Putative Batesian mimicry of gelatinous zooplankton by larvae of marine fishes: a closer look based on in-situ images by blackwater photographers

Examination of photographs and videos of living epipelagic oceanic larval fishes and invertebrates obtained during night dives provided heretofore unavailable information on the appearance and behavior of these organisms. The raw data were provided by numerous “blackwater” divers in oceans around the world. Extraordinary elaborations of fin rays, body form, and other morphological features of the fishes were observed to present similarities in appearance to common noxious, unpalatable, and low-energy content invertebrates in the same environment, especially cnidarians. Much has been written about the possible functions of these structures, with the recognition that they must come at a price in terms of active predator avoidance, i.e. they create varying levels of drag and thus inhibit rapid swimming and maneuvering. Among the most commonly suggested of these is Batesian mimicry of toxic or “nutritionally barren” gelatinous zooplankton such as jellyfish and siphonophores. These observations support the previously suggested hypothesis that many highly predation-vulnerable larval fishes are gaining protection by resembling unpalatable and dangerous invertebrates. This mechanism is one of several ways larval fishes may avoid predation. Evidence for Batesian mimicry is further supported by observations of direct associations between fishes (and some vulnerable invertebrates) and cnidarians. This phenomenon is designated as protective commensalism. Batesian mimicry by oceanic larval fishes appears to have evolved in at least 15 orders and dozens of families of fishes. Many examples of potential mimic and model pairs are illustrated here in photographs. The study concludes with some suggestions for future work on documenting and understanding the origin and nature of Batesian mimicry in the early life history of marine fishes.