Abstract

We analysed the trophic ecology of the early ontogenetic stages of six mesopelagic fish species (Bathylagoides argyrogaster, Argyropelecus sladeni, Sternoptyx diaphana, Diaphus vanhoeffeni, Hygophum macrochir, and Myctophum affine), which have different morphologies, vertical distributions, and taxonomic affiliations. The larvae and transforming stages of the sternoptychids fed both during the day and at night. However, larvae of the other species fed during the day, as they apparently rely on light for prey capture. The transforming stages of myctophids showed a similar daylight feeding pattern to their larvae, but in D. vanhoeffeni both day and night feeding was evident, thereby indicating the progressive change toward the adult nocturnal feeding pattern. The number of prey and their maximum sizes were linked to predator gut morphology and gape size. Although the maximum prey size increased with predator development, postflexion larvae and transforming stages also preyed on small items, so that the trophic niche breath did not show evidence of specialization. In all the species, copepods dominated the larval diet, but the transforming stages were characterized by increasing diet diversity. Despite the poor development of these early stages, Chesson's selectivity index calculated for larvae and transforming stages showed positive selection for particular prey.