26 Jul 2019
Several galjoen (Dichistius capensis) serenely swim past. They are followed by large dusky cob (Argyrosomus coronus) and a grim-looking Garrick (Lichia amia). A spotted gully shark (Triakis megalopterus) of more than a metre long comes up very close as it leisurely trails the others. The acrylic pane between fish and visitor is almost ten centimetres thick. The main tank, filled with 32000 litres of ocean water, is twelve metres long, eight metres wide and 4.5 metres deep. It is home to 13 fish species which occur in the surf zone off the Namibian coast. A smaller and shallower tank houses guitarfish (Rhinobatos annulatus), common eagle rays (Myliobatis aquila) and Blue-spotted stingrays (Dasyatis marmorata). Other small tanks hold juveniles of various species as well as lobsters, a serpent eel (Ophisurus serpens) and a multitude of molluscs that inhabit the ocean’s intertidal zone.
André van Niekerk is in charge of the Swakopmund aquarium of the Ministry of Fisheries and Marine Resources since the beginning of February this year (2019). He points out that 25 percent of the water in the main tank is replaced with fresh sea water every day. Some fish have been in the huge tank for several years, while others struggle to survive there. Dusky cobs are easy to keep in captivity, says Van Niekerk, and some of them have been with the Swakopmund Aquarium for 15 years. On the other hand there is currently just one specimen of silver cob (Argyrosomus inodorus). As yet it is not known why this species struggles to adapt and rarely survives in captivity.
It is difficult to tell the two cob species apart. The dusky cob occurs mainly in the slightly warmer northern waters, north of Cape Cross and along the Skeleton Coast, while the silver cob is found between Cape Cross and the Orange River estuary in the south.
Surf fish must be handled with the utmost care, Van Niekerk emphasizes, and not only so that they survive in captivity. Sport and recreational anglers also need to treat the fish gently. A fish must not be dragged across the beach or sand under any circumstances, it must not be touched unnecessarily and if it is to be returned to the water it should be done as quickly as possible and without inflicting injury. When fish are caught which are too small, or too many of a particular type or size, or which are not wanted, they have to be held in shallow water to carefully remove the hook before being released. Fish must never be thrown back into the water or just left lying on the beach.
Ichthyologists have found that fish developed conspicuously strong bacterial and mould growth where the protective layer of mucus had come off because they had been touched by human hands. Later the fish died. Van Niekerk warns that fish should never be touched with dry hands and that the gills should never be touched at all. Smaller fish should rather be held on the lower jaw. Furthermore he appeals to anglers to refrain from catching fish merely for the fun of it after they have fulfilled their legal quota. Those fish are unlikely to survive because they will probably not be handled correctly, he says.
A visit to the Swakopmund aquarium is always worthwhile. It showcases only fish species which occur at the Namibian coast.
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