In a period mainly from 1995 to 1998, 19 species of southern temperate and subtropical mesopelagic fish have been caught in Norwegian blue whiting, Micromesistius poutassou (Risso), surveys in the Rockall Trough area. Six of the species have not previously been recorded that far north, and the other 13 only rarely in adjacent waters. The species were of the following families: Stomiidae (four species), Microstomatidae (one species), Bathylagidae (one species), Opisthoproctidae (one species), Myctophidae (four species), Evermannellidae (one species), Nemichthyidae (one species), Derichthyidae (two species), Melanonidae (one species), Melamphaidae (one species), and Chiasmodontidae (two species). We discuss whether these range extensions are real and attributable to the recent ocean warming, or only apparent, caused by increased sampling effort.