LIPID-CLASS COMPOSITION OF ORGANS AND TISSUES OF THE TIGER PRAWN PANAEUS-ESCULENTUS DURING THE MOLTING CYCLE AND DURING STARVATION

Neutral lipid and phospholipid fractions and their component lipid classes in the digestive gland, abdominal muscle, epidermis and cuticle of Penaeus esculentus Haswell were analysed and compared during the moulting cycle and during starvation. The prawns were collected from Moreton Bay, Queensland, Australia, by trawling during 1985-1987, and were fed on a standard, semi-purified diet. The digestive gland appears to be a major site of lipid synthesis, storage and mobilisation in preparation for moulting. Neutral lipid, 59 to 80% of which was triacylglycerol, was the larger fraction. It accumulated during early premoult, mainly due to the increase in triacylglycerol. The digestive gland contained only 18% of the total body lipid, or 8% of body lipid as triacylglycerol. Thus, the reserve lipid available for energy production is very small. Digestive gland triacylglycerol was markedly depleted after 4 d starvation and was almost completely absent after 8 d. In the other tissues, the major fraction was phospholipid, of which over 50% was phosphatidylcholine and up to 20% phoshatidyl-ethanolamine; cholesterol was the major class in the neutral lipid fraction and appeared to be very stable. Most of this lipid was probably a component of cellular membranes. The lipid composition of muscle changed very little during the moulting cycle: total lipid levels in the epidermis were high in late premoult and early post-moult, when new cuticle is being secreted, but the proportions of the component lipids were closely similar. Cuticle lipid, together with other major components, was resorbed from the old cuticle prior to ecdysis, but the cuticle phospholipids appeared to be labile at all moult stages. The total of all lipids in fed P. esculentus was about 3.6% dry weight, of which about 70% was phospholipid. Earlier research had shown that when digestive gland lipid is exhausted after a short period of starvation, muscle is metabolised for energy. The present research showed that in the remaining muscle only about 13% of lipid was lost after 21 d starvation, mostly as phosphatidylcholine. This is in keeping with the need to maintain this tissue in a functional state. In contrast, epidermal lipid levels were markedly reduced after only 4 d starvation and the proportions of phospholipids changed significantly. This sensitivity of the cuticle lipids to starvation may be the cause of delayed moulting, which is characteristic of poor nutrition.