Abstract
In Oslofjorden Meganyctiphanes norvegica seems to feed more intensively and has a more varied diet than Thysanoessa raschi. This is consistent with the former species' greater heterozygosity for gene loci coding for enzymes that take part in metabolizing externally derived substances. The two species' similar values for average heterozygosity in those genes coding for central metabolic enzymes may reflect the similarity of their physical habitats. On the other hand total average heterozygosities, 3.2 % for T. raschi and 5.6 % for M. norvegica, are the lowest thus far measured for euphausiids and may be in accordance with hypotheses on low genetic variation in fine-grained strategists.