Oxygen respiration and metabolic enzyme malate dehydrogenase of Euphasia superba in the South Atlantic Ocean

Besides vertebrates, melatonin has been detected throughout phylogeny in numerous non-vertebrate taxa. In the present study, the occurrence of melatonin in Antarctic krill Euphausia superba and its possible role in mediating seasonal metabolic changes was evaluated.

Melatonin was quantified by enzyme linked immunosorbent assay (ELISA) in high performance liquid chromatography (HPLC) purified extracts of eyestalks and hemolymph of krill sampled in the Lazarev Sea during the Antarctic winter and summer. In addition, oxygen uptake rates and the activities of the metabolic enzyme malate dehydrogenase (MDH) were recorded to assess the metabolic status of krill. Validation of melatonin measurements was carried out on the basis of three different extraction methods with parallel determination of melatonin by ELISA in crude extracts and in HPLC purified extracts, and after derivatization of melatonin under alkaline conditions in the presence of hydrogen peroxide.