Lipid class requirements of juvenile slipper lobster, <i>Thenus australiensis</i>
Creators: name: Landman, Michael
Publisher: name: University of Tasmania
Year: 2024

description: Scyllarid (slipper) lobsters, and the closely related Palinurid (spiny) lobsters, differ from most other decapods in that they have pelagic phyllosoma larvae, a post-larval puerulus or nisto stage, possess enlarged or modified antennae and lack chelae (claws). There has been broad research on the culture and nutrition of spiny lobsters, yet there is a shortage of comparable information for slipper lobsters. Slipper lobsters of the genus <i>Thenus</i> are regarded as the most economically important group. <i>Thenus</i> spp. are a particularly promising aquaculture candidate group due to their short larval stage, rapid growth, minimal cannibalism while in captivity, and good market value. Recent breakthroughs in closing the larval life cycle and development of proprietary hatchery technology have made possible the mass-rearing of slipper lobsters which has enabled the opportunity now to undertake important research to improve our fundamental understanding and address critical knowledge gaps.<br>This thesis aims to improve understanding of juvenile <i>T. australiensis</i> nutritional requirements, primarily through the examination of dietary lipid class requirements, for the purposes of developing and enhancing the commercial viability of land-based slipper lobster aquaculture. Before lipid specific investigation could occur, there was first a need to better understand normal changes in physiology and nutritional condition over the moult cycle, develop preliminary experimental feeds and improve experimental husbandry practices that support good feeding and comparative growth assessments.<br>Potentially important changes in physiology and nutritional condition over the moult cycle have not previously been described for slipper lobsters. Chapter 3 of this thesis examined the changes in physiological and nutritional condition of hatchery-reared juvenile<i> T. australiensis</i> when maintained on a high-quality natural diet and showed pronounced cyclical changes that were consistent with generalised models of crustacean growth. Additionally, the haemolymph refractive index (measured as Brix) was validated as a viable non-destructive method for predicting physiological status and nutritional condition. An experimental feed study was subsequently conducted in Chapter 4 to benchmark juvenile growth performance against a natural fresh food source, establish the potential minimum co-feeding requirement without compromising experimental feed formulations, and refine experimental system and husbandry practices. The study found that although a diet of fresh mussels (<i>Mytilus galloprovincialis</i>) provided superior (2-fold) growth performance, adequate growth could still be achieved with an unoptimised preliminary feed formulation in the absence of an incorporated fresh feed component. Dry matter (DM) feed intake was strongly implicated in the different growth rates achieved between the fresh and formulated feeds.<br>Following an extensive literature review on crustacean dietary lipid requirements (Chapter 2), initial lipid nutrition experiments were designed to separately examine the essentiality of dietary phospholipid and cholesterol, respectively. In Chapter 5, the primary objectives this experiment were to test the hypothesis that dietary phosphatidylcholine (PC) is essential for juvenile <i>T. australiensis</i> and would have beneficial effects on lipid utilisation and digestibility of fish oil TAG. This experiment found that dietary PC at any inclusion level from 0.05 to 1.43% DM had no significant effects on any measured endpoint and that dietary PC is probably not essential owing to an apparent capacity for endogenous biosynthesis far exceeding possible dietary uptake. Since crustaceans appear to have limited capacity for <i>de novo</i> synthesis of cholesterol they must obtain it from the diet. However, requirements vary from species to species and can be influenced by the presence of other dietary nutrients. Therefore, the objective of Chapter 6 was to test the hypothesis that dietary cholesterol is essential for normal growth and development in early juvenile <i>T. australiensis</i> and to explore the potential for interactions between dietary cholesterol and phospholipid (PhosL). This study found that juvenile <i>T. australiensis</i> fed 0% DM dietary cholesterol (approx. 0.05% measured in feeds) had significantly lower ultimate feed intake, moult frequency, growth, survival and nutritional condition compared to those at 0.2 or 0.4% DM dietary cholesterol. Mixed PhosL from refined soy lecithin improved feed efficiency at all dietary cholsterol inclusion percentages, but did not provide any meaningful additional benefits. Although essential, dietary cholesterol requirements for juvenile <i>T. australiensis</i> appear to be relatively low at ≤ 0.2% DM, and the higher dietary inclusion content of 0.4% DM did not provide any obvious benefit.<br>This research project aimed to develop a deeper understanding of the practical and functional lipid requirements of juvenile <i>T. australiensis.</i> Lipid nutritional requirements of even the most intensively studied crustacean species reveal differing essentiality and practical requirements, which may exhibit equivocal interactive effects with other nutrients. Therefore, it is important to establish nutrient essentiality and quantitative requirements on a case-by-case basis, particularly for such high-value aquaculture species where rapid growth, cost-effective feeds and waste minimisation are key to economic and environmental sustainability. In the absence of specific nutritional requirement data, and adequate functioning artificial diets for the species, fundamental research was required to understand physiological changes over the moult cycle and develop initial feeds and experimental practices as a foundation for subsequent research. The research contained within this thesis revealed cyclical and highly significant changes in physiology and nutritional condition can occur naturally over the moult cycle, and that meaningful growth responses could be achieved with unoptimized formulated feeds. It also revealed that dietary PhosL (as either PC or mixed PhosL) is not essential for juvenile <i>T. australiensis</i> and that while dietary cholesterol is essential, actual requirements are relatively low. This body of work makes an important first step toward improving our understanding of the physiology, culture conditions and lipid nutritional requirements of juvenile <i>T. australiensis.</i><br>