Protein and lipid nutrition of juvenile southern rock lobster, Jasus edwardsii (Hutton)

Recent interest in the aquaculture of southern rock lobster Jasus edwardsii has developed with increasing demand for lobsters and declining wild fisheries. The potential economic success oflobster aquaculture will depend on the development of efficient formulated feeds specifically designed to meet the nutritional requirements of this species. Experimental lobster feeds are currently based on fish meal and fish oil formulations, and although good survival and growth up to that of lobsters fed fresh blue mussels has been achieved, the potential to increase growth through nutrient level manipulation has not been achieved to date. Investigations of appropriate experimental methods, and subsequent determination of ingredient digestibility, lipid utilisation, histological assessment of energy storage, lipid class and fatty acid composition and energy substrate for metabolism were performed through a series of experiments with juvenile J edwardsii. Apparent digestibility of protein and carbon from novel dietary ingredients was assessed to screen potential protein sources for dietary inclusion. The apparent digestibility of crude protein in mussel meal (98%), prawn meal (77%), and lupin flour (100%) were higher than the current standard fish meal (63%), and the defatting of fish meal decreased the apparent protein digestibility (53%). Squid (7%) and canola meal (38%) were poorly digested by lobster. The examination oflobster metabolism when fed varying protein levels was measured through oxygen consumption and ammonia-N excretion and their atomic ratio. Lipids were metabolized in feeds containing low protein levels, and carbohydrate and protein were metabolized in high protein feeds, and suggested that carbohydrates were not well utilised. Isonitrogenous and isolipidic diets were formulated to include a range of potential protein meals and lipid sources, to assess the effect of lipid composition and source on the growth and composition of juvenile lobsters. Fish oil was replaced with vegetable and alternate marine oils in formulated feeds with no significant reduction in weight gain (1.2 - 2.87 g), however lobsters fed the reference feed (fresh blue mussel, Mytilus edulis) gained more weight than those fed formulated feeds (5.65 g). Lipid class analysis of the digestive gland lipids indicated high levels of triglycerides (TAG) and diglycerides (DG) in the digestive gland oflobsters fed fresh mussels (FrM), mussel meal (MM) and fish oil with lecithin (FOL). High TAG and DG were associated with digestive gland lipid storage, and were correlated to high productive protein values (r=0.755, P=0.005, n=12). Lipid histology of the digestive gland confirmed lipid deposition as droplets in R-cells, and the presence of abundant reserve cells in the digestive gland of fast growing lobsters was observed. Dietary phospholipids produced the fastest growth rates in FrM and MM, while dietary triglycerides did not promote growth. Fatty acid composition of lobster digestive gland closely resembled the dietary lipid profile however the predominantly structural lipids in the whole body tissue, more strongly reflected the profiles of control lobsters. The addition of lecithin to fish oil improved the deposition of lipid droplets in the digestive gland. This study provides greater understanding of the interactions between dietary ingredients and their effects on protein and lipid metabolism, retention and growth and provides valuable information to develop formulated feeds for J. edwardsii.