Physiological and transcriptomic analysis across the life-cycle of the ornate spiny lobster, Panulirus ornatus, for sustainable aquaculture production

Courtney Lewis

doi:10.25907/00802

Spiny lobsters are a key economical resource, forming the basis for major fisheries in both tropical and temperate zones. Following on from the ever-increasing demand for spiny lobsters resulting in fully exploited fisheries, sustainable aquaculture is the way forward to meet the high commercial demand for the ornate spiny lobster, Panulirus ornatus. This tropical species is a prime candidate for aquaculture due to its high market value in addition to its short larval phase. Recently, at the Institute for Marine and Antarctic Studies (IMAS), the life-cycle for this species was closed, providing the unique opportunity to study P. ornatus across the various morphology distinct life stages. The complex life-cycle of this species poses a significant challenge to the success of closed life-cycle culturing, and overcoming this has been a major focus for research in recent years. This research aims to contribute to this effort through combining physiological and molecular approaches to characterise the molecular pathways that regulate the growth and development in P. ornatus. Beginning with embryo development, a comprehensive transcriptome was established, encompassing 11 stages across P. ornatus embryogenesis. Key genes associated with development were characterised in addition to the development of hatch prediction models based on visual parameters to bring characterisation to the embryo development of this species. This provides a basis for defining a staging system for P. ornatus embryos and other lobster species. Following on from successful embryo and larviculture tools at IMAS, the focus turned to juvenile rearing. The challenges facing this life stage largely surround the moulting and nutrition. Juvenile P. ornatus moult frequently as they grow, making them ideal candidates to investigate the relationship of physiology and genetics through this development period. P. ornatus juveniles were assessed every three days across a complete moult cycle for physiological parameters, including Brix to approximate hemolymph protein and hemolymph ecdysone concentration. In addition, chitin metabolism was also investigated. Chitin was assessed through establishing a fluorescence-based assay to quantify chitin content in juvenile P. ornatus across the moult cycle. Nutritional condition of juvenile P. ornatus was examined across the moult cycle, assessing whole-body proximate composition, in addition to histological and transcriptomic analysis of the hepatopancreas. The rise in gross energy and dry matter across the moult cycle is reflective of the rapid nutrient accumulation occurring across moult cycle in addition to the variable protein and lipid content. A pattern in both lipid content and expression of lipid metabolising genes across the moult cycle was inconsistent with what has been previously established about the utilisation of lipids in crustaceans throughout moulting. The final investigation was the ontogeny of Cytochrome P450s (CYP450s) in P. ornatus. Whilst CYP450s are a diverse family of enzymes, CYP450s associated with steroidogenesis are well conserved across arthropods, due to their role in the synthesis of the active moult hormone and are well characterised. CYP450s were characterised across the life-stages and tissues of P. ornatus, displaying their roles in ecdysteroidogenesis, as well as highlighting unannotated CYP450s with similar expression profiles that may have functions in steroidogenesis or other important growth and development pathways. In summary, the research presented provides a comprehensive analysis of the important developmental pathways in the ornate spiny lobster, presenting two additional transcriptomic libraries for this species highlighting genetic changes across life-stages and tissues. This provides a strong foundation for further research into identifying the functions of genes associated with key growth and development pathways to assist in improvements of the sustainable aquaculture production of P. ornatus.

Physiological and transcriptomic analysis across the life-cycle of the ornate spiny lobster, Panulirus ornatus, for sustainable aquaculture production

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