Mouth size and predator strategy of midwater fishes

Abstract

It has been suggested that bathypelagic fishes should be equipped to eat any large or small food item that they should chance to meet in their relatively impoverished environment. The derived hypothesis that bathypelagic species are trophically generalized was indirectly substantiated in two taxonomic groups of midwater fishes. Bathypelagic members tend to be larger and have larger mouths than their mesopelagic relatives, but still have a well-developed pharyngeal basket for retaining small items. Bathypelagic offshoots of the primarily mesopelagic group of lanternfishes seem to have acquired larger mouths at the presumed metabolic expense of having proportionately larger bodies. The deeper-living members of the primarily lower mesopelagic or bathypelagic family Melamphaidae are further specialized in that they have disproportionately larger mouths with minimum additional body size. This discussed relative to theoretical considerations of foraging strategy and metabolic economy.