Studies on the physiology of a shrimp, metapenaeus sp. (crustacea: Decapoda: Penaeidae): IV. carbohydrate metabolism

By use of a closed recirculating system for carbon dioxide collection, it was found that the greater part of [14C]glucose, either fed or injected, appeared asCO within 24 hr. Up to 2 % was incorporated as polysaccharide. Extract of sensory-pore-complex did not affectC distribution but eyestalk ablation reducedC0, output to about two-thirds, with a corresponding increase in body carbohydrateC. A small amount of the 14C was incorporated in both carbonate and non-carbonate fractions of the cuticle. Eyestalk ablation caused a highly significant reduction in blood reducing substances, while sensory-pore extract caused a significant increase. Blood of intermoult animals contained 39·2-42·0 pg/ml glucosamine in plasma proteins, and 3·3-4·0 pg/ml in cells, but in premoult animals plasma content fell to 10 pg/ml and cells increased to 72·3 pg/ml. Eyestalk ablation reduced plasma glucosamine only, while sensory-pore-complex extract raised total blood glucosamine slightly. Glucosarnine of the epidermis increased 10-fold following eyestalk ablation. On the assumption that hexosamine comprises about one-third of the total sugars in mucopolysaccharides, mucopolysaccharide: glycogen ratios were calculated as 1: 1 for epidermis, but were 5·3: 1 for digestive gland, due to epithelial mucins involved in digestion. Oxidation of [C] glucose in Metapenaeus, Metapograpsus, and Hemigrapsus are compared, and it is suggested that glycogen does not play a major role in Metapenaeus, the animal being-de-a endent on a sustained intake of food for both oxidative metabolism and chitin synthesis. “Moult-accelerating hormone” of the sensory-pore-complex may be a hyperglycaemic hormone responsible for mobilization of body carbohydrates. It is suggested that an acid mucopolysaccharide is supplied by the blood to the epidermis as a chitin precursor, the source being blood amoebocytes