| Summary: | We investigated the effect of short-term starvation (18 days) on the physiology of adult Euphausia superba from the Lazarev Sea at the onset of summer. Metabolic data, elemental and biochemical composition as well as morphological parameters revealed that, at the beginning of the experiment, krill was in transition from winter to summer physiology, with some features typical for late winter/spring (low lipid reserves, low C:N ratio, elevated ON ratio) and others for summer (high respiration rates, high MDH activity, large green digestive gland, short intermoult period (IMP) and fast growth). Starvation reduced body reserves drastically by more than 1% C per day. In relative terms, lipids (40%) and glycogen (30%) were reduced most and proteins by 10% of the initial value. Absolute consumption, however, was approximately 4% DM for lipids and proteins each, whereas contribution of glycogen was negligible. Within lipids, triacylglycerols (TAG) and phospholipids (PL) fell most dramatically from already low levels by 84% and 39%, respectively. Phosphatylcholine (PC) constituted 57% of PL and declined by 46%. As a result, proportions of the lipid classes changed with sterols increasing relatively. Metabolite changes were similar in cephalothorax and abdomen, although TAG in the cephalothorax fell more drastically. High metabolic activity at the beginning of starvation was quickly reduced to reach 53% after 18 days, accompanied by a reduction in the abdominal activity of malate dehydrogenase (MDH) by 25%. Our results may provide some explanation why recruitment of some year-classes of krill fails. Despite execution of the experiment in spring (i.e. transitional physiology state) and its short duration, some changes in the activity of metabolic enzymes in the abdomen, representing lipolytic, glycolytic and proteolytic pathways, respectively, were measured. Rising activities of 3-hydroxyacyl-CoA dehydrogenase (HOAD) and glyceralaldehyde-3-phosphate dehydrogenase (GAPDH) indicated increased lipolytic and glycolytic fluxes, ...
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