An assessment of the suitability of the galjoen, Coracinus capensis cuvier, for mariculture in South Africa

Master Thesis


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University of Cape Town

The suitability of the galjoen, Coracinus capensis, for mariculture in South Africa has been assessed from both an economic and a biological viewpoint. In terms of economic criteria galjoen shows a high potential for culture, being widely known and highly regarded as a table fish. The restaurant trade in the southwestern Cape has been identified as a possible market showing a high demand for this species. Adult galjoen are readily available, hardy, and are easily maintained in captivity. A biochemical technique to determine the sex of live fish has been elucidated and allows sexual identification to be conducted for several months prior to and during the spawning season. Natural serial spawning with high fertilization occurs readily in captivity, with galjoen producing large numbers of good quality eggs during a single season. However induced spawning using two mammalian gonadotropins resulted in the production of poor quality eggs. The relationship between temperature and development time for fertilized galjoen eggs has been determined, and the lower lethal temperature for developing eggs was found to lie between 14° and 16°C. Newly-hatched larvae exhaust their endogenous food reserves rapidly and show a short time to irreversible starvation, with first-feeding beginning from 110 hours after hatching at 18°C. Galjoen larvae proved to be extremely difficult to rear. Although successful first-feeding on a few live food organisms was observed, mass mortality at 4-8 days and again at 12-15 days after first-feeding resulted in exceptionally poor survival. It is surmised that galjoen larvae have very stringent nutritional requirements which cannot be met by employing commonly-used live food organisms. Growth rate estimates for galjoen that survived past metamorphosis indicate that growth under culture conditions is similar to that in the natural environment. Certain biological attributes of the galjoen such as simple broodstock maintenance, ease of natural spawning in captivity and high fecundity select this species for culture. However the inability to mass rear larvae through to metamorphosis drastically reduces the suitability of this species, especially since larval rearing is the key to successful mariculture. In addition, the slow growth rate under culture conditions observed also selects against this species. Because of these last two factors, it is concluded that the galjoen is not a suitable species for mariculture in South Africa.

Bibliography: pages 151-184.