Transcriptomic and nutritional analysis of the hepatopancreas in cultured juvenile Panulirus ornatus throughout the moult cycle

Juveniles of the ornate spiny lobster, Panulirus ornatus, grow rapidly through frequent moulting events, requiring them to accumulate sufficient nutrient reserves to fuel the energetically demanding process of ecdysis. As moulting events occur so often, especially in the early-stage juveniles, it is critical that the juveniles maintain adequate nutritional condition throughout the moult cycle for maximum survival. This is especially important for animals housed together on a larger scale within commercial culture environments for ensuring maximum survival. In this study, the nutritional condition of juvenile P. ornatus examined over the duration of a moult cycle from the 7th to 8th juvenile moulting events. Nutritional condition was measured through biochemical composition analysis as well as histological and transcriptomic examination of the hepatopancreas. The rapid accumulation of nutrient reserves was evident by the increase of dry matter and gross energy over the moult cycle. Six days following ecdysis, there was a significant reduction in total lipids consistent with a downregulation of genes associated with lipid metabolism. Histological examination of the hepatopancreas did not illustrate any changes in the cell distribution or morphology associated with the consistent drop in total lipids and associated metabolic pathways suggesting the involvement of other regulatory mechanisms. The present study is the first to investigate biochemical changes over the duration of a moult cycle in early juvenile stages of P. ornatus, imperative for enhancing the understanding of energy demands of undergoing frequent ecdysis and provides insights into nutrient utilisation for this species.