Aquafeed development of juvenile slipper lobster (<i>Thenus australiensis</i>)
Creators: name: Williamson, Andrea
Publisher: name: University of Tasmania
Year: 2024

description: <i>Thenus</i> spp. are prevalent and important seafood species in the Indo-West Pacific region. However, in Australia, the supply of <i>Thenus</i> spp. is limited as it depends mostly on by-catch from the scallop and shrimp fishery, with minor input from a commercial hatchery and grow-out operation producing a soft-shell juvenile product (Australian Bay Lobsters, Northern NSW). <i>Thenus australiensis</i>, the most abundant <i>Thenus</i> sp. in Australian waters, is a promising candidate for intensive closed-cycle aquaculture because of its short larval development phase, rapid growth, minimal cannibalism in captivity, and high commercial value. Following the closure of the larval life cycle and the development of commercial hatchery technology for this species, the establishment of aquaculture depends on developing a nutritionally adequate and cost-effective formulated feed for the juvenile stages. In terms of feed formulation, protein is a crucial macronutrient supplying energy as well as meeting nutritional requirements for essential amino acids. The primary aim of the present thesis was to document and quantify relationships between feed formulation, nutrient intake, and retention in juvenile <i>T. australiensis</i>. A secondary aim was to evaluate and refine established nutritional experiments to improve their outcomes for feed development. In a broader context, the present thesis aimed to provide a higher understanding of protein requirements with respect to protein availability and quality while improving our knowledge of juvenile lobster nutritional physiology. Lastly, the present thesis aimed to collect data for developing a preliminary factorial model providing practical and valuable information to assist the development of formulated feeds with an optimised digestible protein and digestible energy ratio for juvenile T. australiensis. In detail, the present thesis consists of five interlinked but independent chapters, providing empirical data for developing a preliminary factorial model <b>(Chapter 6)</b> and addressing the following: the apparent digestibility of alternative protein sources to improve feed formulation <b>(Chapter 2)</b>, the inclusion of stable isotope analysis to determine protein sources contribution to growth <b>(Chapter</b> <b>3)</b>, the application of whole-body protein synthesis for nutritional assessment <b>(Chapter 4)</b>, and the determination of varying dietary protein effects on growth response and tissue composition <b>(Chapter 5)</b>.<br>Apparent digestibility and gastrointestinal evacuation rate were measured to assess the potential of five commercially available protein sources for their dietary inclusion. The apparent digestibility of crude protein ranged from 80% to 95%, with crude protein in fish meal significantly less digestible than lupin meal, squid by-product meal and solvent-extracted soybean meal. Lobster completed gastrointestinal evacuation (≥95%) between 4 h (lupin meal) to 6 h (squid by-product meal), indicating that more digestible protein sources have slower evacuation rates. Stable carbon and nitrogen isotope analyses revealed that squid by-product meal, soybean meal and krill meal achieved the highest growth performance and survival, and squid by-product meal and fish meal were the only protein sources assimilated at approximately their dietary inclusion level. The present thesis demonstrated that integrating stable isotope analysis into a growth experiment provides a deeper insight into the utilisation of protein sources by the animal. The present thesis also provides the first whole-body isotopic discrimination factors for juvenile <i>T. australiensis</i>, which can be used in future lobster nutrition studies. The present thesis successfully applied a combination of a stoichiometric bioenergetic approach and an endpoint stochastic model as a non-destructive method to investigate the nutritional effect on all major components of whole-animal metabolism, including respiratory gas exchange, nitrogenous excretion, specific dynamic action, metabolic energy substrate use, and whole-body protein synthesis in juvenile <i>T. australiensis</i>. Postprandial oxygen consumption rate, dissolved inorganic carbon, and total nitrogen excretion returned to the pre-feeding stage within 24 h. Protein was the primary energy substrate for 48 h fasted (45% oxygen consumption) and post-feeding lobster (44%). Whilst the secondary energy substrate differed between carbohydrates in 48 h fasted and lipids in post-feeding lobsters. The high protein usage to generate energy was also reflected in lower protein gain (0.06% d-1 ) compared to protein degradation (0.09% d-1 ) and low protein retention efficiency (1.68%). Lobster growth exhibited a linear dose-response to the increased dietary protein levels with no indication of reduced growth at the highest dietary crude protein level of 550.9 g CP kg-<sup>1</sup> (518.2 g DP kg<sup>-1</sup> ). Dietary protein levels also significantly affected whole-body protein, lipid, and energy content, with P55 having significantly higher lipid and energy content than P50 and P45, whereas protein content was not significantly different to P45 but to P50. The results demonstrate that juvenile slipper lobster grew well when fed high protein formulated feed, providing the first insight into the protein nutrition of this species.<br>A preliminary factorial model determining the protein and energy requirements of juvenile T. australiensis was developed by deriving a combination of parameters specified in this thesis. The daily maintenance requirement for digestible protein (DP) was 10.77 mg DP g BW<sup>-1</sup> d <sup>-1</sup> and 477 J DE g BW<sup>-1</sup> d <sup>-1</sup> for digestible energy (DE). The partial efficiency of utilisation for growth above maintenance was 0.45 and 0.58 for DP and DE, respectively. Weight gain as a function of body weight (g BW<sup>-1</sup> d <sup>-1</sup> ) can be described at a temperature of 26 °C by the following equation: WG = 0.040 - BW (g)<sup>0.139</sup> . The whole-body crude protein (CP) and gross energy (GE) contents were independent of lobster weight and were, on average, 455.8 mg CP g BW<sup>-1</sup> and 13.3 kJ GE g BW<sup>-1</sup> on a dry matter basis, respectively.<br>Overall, the present thesis provides a greater understanding of juvenile lobster nutritional physiology and the interactions between dietary ingredients and their effects on protein digestibility, metabolism, retention, and growth. The preliminary factorial model offers practical and valuable information to assist the development of formulated feeds with an optimised DP/DE ratio for early juvenile <i>T. australiensis.</i>