In South Africa, marine fish aquaculture is in its formative stages of research and development. On the east coast of southern Africa in the quiet town of Port Alfred, this new form of aquaculture is being investigated, with promising results.
Spotted grunter, Pomadasys commerrsonnii, and kob, Argyrosomus japonicus have received attention by the Department of Ichthyology and Fisheries Science (D.I.F.S) at Rhodes University with regards to their aquaculture potential.
A number of projects have been undertaken to determine the viability of spotted grunter as a mariculture species but no work has been done in South Africa to determine the viability of kob. Overseas tank ashore and cage culture have proved popular for a number of fish species and it was therefore decided to determine the differences in growth for these two methods of culture in Port Alfred for kob and grunter.
In South Africa, attempts to culture rainbow trout (Oncorhynchus mykiss) in cages have proven futile. Plans for salmon (Salmo salar) farming were even proposed for Saldanha Bay in 1992, but those never materialised. This may be attributed to the competitive markets that exist from overseas salmon farmers and the inability for "beginners" to compete on a global scale.
In South Africa however, marine fish farming can be a success if there is an effort to breed and grow-out an indigenous species that could exploit a local niche market. Both grunter and kob have excellent flavour, filleting and freezing qualities and share a strong market demand.
A Masters project being completed at present by Jerri Mperdempes and supervised by Prof. Tom Hecht at Rhodes University DIFS, investigated the viability of marine cage culture versus that of tank culture of spotted grunter and kob. As cage culture for marine finfish has never been undertaken on an experimental level or even on a commercial level in southern Africa it was vital in determining fish performance under these conditions.
Statistical tests on mean daily weight gain, specific growth rate, feed conversion ratio, survival rate and condition factor of wild-caught juvenile kob and grunter were evaluated in both land-based tanks and in cage facility. This data were then used to determine the viability of these species under commercial conditions.
Kob shows an abnormally high growth rate under moderate stocking densities in cages with up to 1.5 kg of growth in a year. Growth displayed by grunter is similar to that of most finfish cultured around the world with about 400 g of growth a year. Kob growth is significantly better in cages than in tanks, whereas grunter performs well in both cages and tanks. From a costing point of view, both species will cost less to grow out in cages.
This study has shown that the aquaculture potential of kob and grunter is promising and could be farmed commercially. Funds need to be made available so that studies can be undertaken to condition broodstock, and to spawn and rear larvae. The time has come to start farming indigenous marine finfish.
By Jerri Mperdempes
Dept. of Ichthyology and Fisheries Science, Rhodes University, Grahamstown, 6170
