Abstract
Micro-crustaceans are commonly used in environmental investigations and risk assessment of chemicals. For ecologically sound outcomes of such studies, it should be mandatory to have knowledge about the biology of the species tested. Still, information about the basic functionality of e.g. biochemical systems is in most standard test species limited. Here, we present information about levels of 20-hydroxyecdysteroids (20HE) and lipids during various life-stages of the copepod Calanus finmarchicus. 20HE levels were found to be highest in the CIV and CV copepodites, and lowest in the adult males. Females with egg sacs showed amplified 20HE levels compared to newly moulted females and post-hatch females, indicating that 20HE may be important for initiating reproduction. Lipid reserves of newly moulted females were high, while the lipid reserve was only half in females with egg sacs, and post-hatch females had almost no reserves at all. In CV, the lipid levels were higher than in CIV, indicating storage to be used for egg production at the adult stage. In the CV stage, it was assumed that the higher the lipid level, the closer to moulting into adults. A regression line between levels of lipids and 20HE in CV showed a significant correlation between the two, suggesting that the lipids are strongly related to 20HE production. Our results undoubtedly clarify an important link in understanding some of the important biochemical features in micro-crustaceans.