Abstract:
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.
