Fish farming in the Namib Desert

Text and photographs Ron Swilling

The plots that edge the green swathe of the ephemeral Swakop River as it snakes its way towards Swakopmund and the sea, nurture a collection of interesting enterprises. Olives and asparagus flourish, thriving on the brackish water and sandy soil, and a host of vegetables ranging from spinach to oyster mushrooms are grown, providing a bounty of greens in the Namib Desert.

New and intriguing business ventures are continually being initiated. Two recent examples are the Desert Hills !nara oil and cosmetic range produced from the hardy desert plant, and… freshwater fish, one of the most unusual business ventures in this part of the Namib Desert.

In a coastal area that attracts scores of marine anglers to gather on the desert beaches from Mile 5 and Henties Bay to Torra and Terrace Bay, and in a country whose only perennial rivers are on its peripheries, freshwater fish are a strange and novel concept. The scenario is different in the north-central region, the Ovamboland of old, where the oshanas (shallow depressions, pans or channels) are seasonally fed by the drainage system of the Cuvelai River that rises in southern Angola in the rainy summer season, providing a much-needed source of freshwater fish for the people in the area, while in the Caprivi and Kavango regions local inhabitants depend on the freshwater fish from the Okavango, Kwando and Zambezi rivers for their sustenance and livelihood.

So, far from the northern regions of the country, Manfred Grabow braved the desert and developed tilapia farming, introducing the concept of freshwater fish to the western part of the country.

Tilapia are fairly common in the rest of Africa. They are a popular angling species and the fifth-most important aquaculture fish in the world.

Manfred farms with the indigenous threespot tilapia, Oreochromis andersonii, found in Angola, Botswana, Namibia, Zambia and Zimbabwe. The blue-grey fish with three spots on its side occurs in the Kunene, Okavango, upper Zambezi and Kafue river systems. It is under threat in the Kafue and upper catchment areas of the Zambezi, due to the introduction of an alien species Oreochromis niloticus, and was listed as Vulnerable on the IUCN Red List of Endangered Species in 2007.

Manfred is a cattle breeder and peanut farmer (‘…like Jimmy Carter’, he says) who hails from the Omaheke Region in central-eastern Namibia. When he retired two and a half years ago, he found a twelve-hectare plot on the Swakop River that was ideal for fish farming. His son had studied aquaculture in Germany and encouraged him to start farming fish in his farm reservoirs for his own consumption before his retirement.

Manfred attended an aquaculture course in Windhoek and then in Grahamstown, learning the more sophisticated methods of fish farming. He took some of his stock with him to Swakopmund and began his aquaculture project as a hobby with four small ponds. Before he knew it, he had four large pools and four ponds with a multitude of fast-breeding fish to manage and maintain, and had erected a windmill to aerate the water.

It soon becomes apparent that farming tilapia entails maintaining a fine balance at all times

Like most Namibians I know very little about fish farming! I am taken on a tour around the ponds, where darting schools of fish catch the sunlight as they disappear into the depths in flashes of silver and gold. I am given a crash course on the basics of tilapia aquaculture, which continues in the Grabow’s lounge as Manfred and his wife, Iris, explain the intricacies. It soon becomes apparent that farming tilapia entails maintaining a fine balance at all times: the pool water needs to be kept clean and warm, but not too clean, as the fish need the algae to survive and raise their young. By measuring the oxygen in the water every morning and evening, Manfred determines how to regulate feeding and when to clean.

The water needs to be aerated more at night than during the day, as the algae produce oxygen in the day and carbon dioxide at night, and the fish require additional oxygen to digest their food at night. The temperature also needs constant monitoring. When the weather cools down, the fish require less food and production drops. To keep production up in the winter months, the water must be heated.

Already overwhelmed by the complexities involved, I continue listening to the couple, tuning into my own nature show. Tilapia are mouth-breeders, with the female brooding the fry (young fish) in the mouth, letting them out when they are big enough. They swim back at any sign of danger. In aquaculture there is a huge emphasis on controlling the breeding process with the correct selection of males and females, and separation of the sexes. Unlike many other fish farmers, Manfred chooses not to use hormones to determine the sex of the fish.

In a burgeoning world where larger sea fish now carry the risk of accumulating mercury, farm-bred tilapia free of pollutants are a healthy alternative

Breeding starts with breeding ‘pairs’ – one lucky male to four females. Keeping an eye on the growth rate is a necessary procedure, separating the fingerlings as soon as they are a certain size, weighing them and moving them to the larger pools to prevent further breeding and overpopulation. Harvesting the fish requires different procedures. Before every harvest, it is necessary to move the fish into smaller holding ponds with clean water, and to refrain from feeding them for several days to ensure that the digestive systems of the fish are clear. This prevents any ‘muddiness’ in the flavour.

As Namibians become accustomed to the notion of freshwater fish, Manfred the cattle farmer becomes an experienced tilapia farmer. He smokes a quantity of the produce and sells some of the freshest freshwater fish to be found south of the Etosha National Park and north of the Orange River. In a burgeoning world where larger sea fish now carry the risk of accumulating mercury, farm-bred tilapia free of pollutants are a healthy alternative.

A large, attractive rendition of a threespot tilapia is painted on the sign at the entrance gate to his property, much to the amazement of passersby. This an unusual sign to see on a sandy road surrounded by a wide expanse of desert.

This article appeared in the August Edition of FLAMINGO Magazine.