The goal of this study was to investigate whether Antarctic krill (Fig.1) possesses a circadian clock and whether such a clock controls key physiological processes of krill. To this end, we investigated temporal mRNA expression levels of the canonical clock gene cry2 in individual krill that were maintained both under a light-dark cycle and constant darkness. In addition, we tested whether gene expression of metabolic key enzymes in these krill show daily or circadian oscillations, and to what extent transcriptional oscillations of these enzymes also persist at the protein-activity level .
 Teschke, M. et al., PLoS ONE doi:10.1371/journal.pone.0026090
Overall, our results showed that a krill endogenous circadian clock governs metabolic and physiological output rhythms (Fig.2). Enzyme activity assays revealed oscillatory patterns with roughly 9-12 h period under both lighting conditions that correlate with the relative changes in transcript abundance. Further studies will be necessary to investigate the contribution of the circadian clock to rhythmic variations in expression and activity of metabolic enzymes in krill and thereby will give a better understanding of how rhythmic physiology and behavior in krill will be regulated. Time course experiments require a standardized and equably homogenization of biological tissues that guarantee a reliable temporal analysis of data. In particular, enzyme assays require a low temperature during the homogenization process to maintain enzyme activity. During this study, the Cryolys guaranteed a constant temperature of +4°C within the homogenization chamber and thus avoided an uncontrolled defrosting of the frozen samples.