Studies have shown that the gut contents of Malacosteus niger are more likely to contain copepod crustaceans than larger animals like fishes or shrimps (Sutton 2005). This is surprising considering its fearsome array of large fangs and huge gape. Its lack of gill rakers also suggests a diet of bigger prey organisms.
So why does M. niger seem to prefer copepods? The answer appears to be that these small creatures provide the chemicals that M. niger uses in its eyes to see red light. These chemicals are known to be derived from chlorophyll (Douglas et al 2000), which the copepods in turn acquire from their diet.
When it gets the chance, however, M. niger will revert to its ancestral feeding habits and devour much larger organisms, before going back to snacking on the copepods.