The use of physiological parameters in the management of the South African abalone (Haliotis midae) aquaculture systems in South Africa
The aquaculture of the South African abalone (Haliotis midae) is the most lucrative and fastest growing division of Southern African mariculture. This industry is driven by a demand far exceeding supply, and natural stocks at the brink of depletion. A study was launched to gather clues from the basic physiological constituents in abalone, which will help in the management of abalone farms in South Africa. In 2003 an intensive literature study was launched to assess the availability of literature on abalone research, and to find research trends in published literature. From 2003 to 2005, basic physiological constituents (Including glucose, glycogen, proteins and lipids) were studied in abalone from six farms in South Africa. A two phased approach was followed, the first of which was an exploratory phase (2003 - 2004) where physiological constituents were studied six-weekly in the muscle tissue and digestive gland of abalone, in two size classes (±50 mm and 70 mm shell length) and four feeding regimes (natural, artificial and two rotational feeds), from one farm. At the end of Phase one, a single live export simulation trial was conducted following standard farm protocols. In Phase two (2004 - 2005), physiological constituents were studied seasonally in the muscle tissue and haemolymph of abalone, in two size classes (±50 mm and 70 mm shell length) and on two dietary regimes (natural and artificial feed), from five abalone farms, of which two had to withdraw from the project. Live export simulations were conducted seasonally in phase two. South Africa is one of the world leaders in publishing abalone research. The main focus of research in South Africa is on the development and enhancement of artificial diets. There is, however, a need for abalone research in South Africa to be diversified. Owing to the variety of functions of the digestive gland, physiological constituents studied in this organ was too variable to be useful for the purposes of this project. It was concluded that digestive gland tissue were not practical to study for farm management practices. Muscle tissue yielded 0.65 - 1.72 g.kg-1 glucose, 11.04 - 88.35 g.kg-1 glycogen, ± 0.08 g-kg-1 haemolymph, 15.99 - 31.64 g.kg-1 lipids and 28.83 - 52.85 g.kg-1 proteins. On average, abalone lost ± 15% of their body mass during simulated export. Season was the most important parameter in the regulation of physiological constituents, and in mass loss experienced during simulated export trials. Different feeding regimes had limited effect on physiological constituents and on mass loss. Animal size influenced mass loss, with small animals being more prone to mass loss than large animals, but did not have pronounced effects on physiological constituents. The results obtained for animals from different farms did not differ significantly. Correlations of physiological constituents with export mass loss indicated that muscle glucose was the only constituents with predictive powers in terms of predicting mass loss during export. Physiological constituents, studied in the muscle tissue, are useful indicators of abalone condition in the aquaculture environment. The artificial feed currently employed by South African farmers is not producing optimal results, and the formulation could be improved to harness the full potential of an optimally balanced diet. The most important factors affecting mass loss during simulated export are animal size and season. By selecting larger animals for export, and by limiting exports during summer months, mass loss during simulated export can be significantly reduced, which will significantly reduce corresponding losses of revenue.