During ontogeny, the increase in body size forces species to make trade-offs between their food requirements, the conditions necessary for growth and reproduction as well as the avoidance of predators. Ontogenetic changes are leading species to seek out habitats and food resources that meet their needs. These aspects are interesting to study in the case of deep pelagic fishes, as a significant part of the community migrates vertically at night to feed in the productive surface layer, while other species remain at depth. To this end, ontogenetic changes in nocturnal habitat (vertical use of the water column) and in the type of food resources (based on stable isotopes of nitrogen) were investigated in 12 species of deep pelagic fish from the Bay of Biscay in the Northeast Atlantic. Our results revealed the existence of major differences in the ontogenetic strategies employed by deep pelagic fishes. Some species showed ontogenetic changes in both vertical habitat use and food resources (e.g. Lampanyctus crocodilus and Melanostigma atlanticum). In contrast, other species showed no ontogenetic change (e.g. Searsia koefoedi and Notoscopelus kroyeri). Some species only changed food resources (e.g. Myctophum punctatum, Arctozenus risso, and Serrivomer beanii), while others seemed to be influenced more by depth than by trophic features (e.g. Xenodermichthys copei and Argyropelecus olfersii). These results suggest that to meet their increasing energy requirements during ontogeny, some species have adopted a strategy of shifting their food resources (larger prey or prey with a higher trophic level), while others seemed to maintain their food resources but are most likely increasing the quantity of prey ingested. In addition, some species opted for a habitat change to greater depths at adult age to limit the energy expenditure associated with migration, while others continued to feed at the surface at night.