Trophic Ecology of the Deep-Sea Fish Malacosteus niger (Pisces: Stomiidae): An Enigmatic Feeding Ecology to Facilitate a Unique Visual System?

摘要

The ‘dragonfishes’ and their relatives (family Stomiidae) are among the top predators of the mesopelagic zone of the open ocean. Based on feeding morphology (e.g., large gape, long fangs, and no gill-rakers or ethmoid membrane), the meso/bathypelagic fish Malacosteus niger would also be expected to be a large-item predator, as are the other members of its family. However, analysis of specimens from different ocean basins revealed that the most common prey items are calanoid copepods, despite an apparent inability to handle such small prey. Malacosteus niger is considered advanced within the Stomiidae, so this feeding mode represents a secondary reversion to planktivory. Feeding mechanics are unknown, but the integration of trophic, visual and distributional ecology may explain this finding. Malacosteus niger is unique in the possession of a chlorophyll-derived photosensitizer (bacterial pheophorbide), which it uses to see its own far-red bioluminescence. This pigment, whose synthesis by vertebrates is unlikely, may be incorporated through an anaerobic phototrophic bacteria-(protist?)-copepod-fish trophic linkage. In essence, the atypical diet of Malacosteus niger may be driven by the need for this pigment rather than by energetics per se.