Biochemical composition and catalytic potential of individual North Sea copepodsCopepods belong to the most important primary and secondary consumers in marine pelagic systems. They are capable of efficiently utilizing different feeds like phytoplankton or other microzooplankton species. In turn, copepods form the principal food source for animals from higher trophic levels such as larvae of fishes. Estimations about transfer rates of matter and energy between trophic levels as well as the classification of food quality requires detailed knowledge of biochemical parameters on an individual level. Therefore, we adapted and optimized analytical methods to determine biochemical composition and enzyme activities of individual North Sea copepods.The dry mass of individual females ranged between 4.9 and 6.6 µg (Acartia clausii, Acartia tonsa, Corycaeus anglicus, Paracalanus parvus) and between 26 and 38 µg (Centropages hamatus, Centropages typicus, Temora longicornis). The relative amount of protein was higher in the smaller species (30 to 40 % of dry mass) than in the larger ones (16 to 19 % of dry mass). Total lipids were determined in groups of 15 to 30 animals with a microplate-assay which was based on the sulphophosphovanillin-method. Total lipid concentrations ranged between 2.4 and 6 % of dry mass. Low lipid amounts were confirmed by low atomic C:N-ratios of 4:1 to 5:1. The overall energy content as calculated from carbon values amounted from 18.3 to 21.1 J/mg dry mass.The activities of a set of digestive enzyme (chitobiase, β-glucosidase, lipase/esterase, and peptidases) were determined fluorometrically. Enzymes showed different levels of activities between species suggesting different traits of enzymatic food utilization. Zymograms of endopeptidases were determined in individual animals. Each species expressed individual and characteristic patterns of enzymes. Intraspecific variation was insignificant.Both Acartia species as well as Corycaeus anglicus had highest relative protein amounts. Acartia clausii, Paracalanus parvus and Temora longicornis showed the highest lipid contents per dry mass. Five species had relative energy values of 20 to 21 J/mg dry mass. Only Acartia tonsa and Corycaeus anglicus had lower energy values of about 18 J/mg. All species were characterized by a high esterase/lipase activity. Centropages typicus as well as Paracalanus parvus and Temora longicornis can be expected to utilize various food items most efficiently. Centropages hamatus and Temora longicornis showed optimal abilities to digest carbohydrates while peptidases were most active in Centropages typicus and Paracalanus parvus.Keywords: North Sea copepods, protein, lipid, C:N, energy, zymograms, digestive enzymes, fluorogenic substrates