Lake Victoria in eastern Africa is the largest tropical lake in the world and the second largest freshwater lake on the planet in terms of surface area. Compared to the other large African lakes, Lake Victoria is a very young like. Many geologists believe that the area where we today can find the largest lake on the African continent was dry as recently as 12,500 years ago. Despite the young age of the lake, a myriad of different species have developed in its waters. Such a diversity of species created under a short period of time is known as 'explosive speciation'. Unfortunately, many of these species have been completely eradicated from Lake Victoria during the last century and others are on the brink of extinction. It is particularly distressing when we think about the fact that a large part of the Lake Victoria species is endemic to the lake. Once they are eliminated from Lake Victoria, they are eliminated from the face of the earth and can never be reintroduced again. A few Lake Victoria species are however successfully bred in captivity today; particularly fishes that display striking colours, tantalizing shapes or fascinating behaviour since these features make them popular among aquarists. The most pressing problems in Lake Victoria today are pollution, oxygen depletion, introduced species, over-fishing and algae growth. The scenario is however not pitch black and there might still be ways of saving Lake Victoria.
One of the encouraging stories is the one about the Water Hyacinth problem in Lake Victoria. Eichhornia crassipes is a water hyacinth native to the tropical Americas. When it was introduced to the pristine Lake Victoria, it thrived and formed thick mats on the surface. This soon led to problems with transportation, fishing, the drinking water supply and the hydroelectric power generation. Fishermen experienced problems in reaching their fishing grounds, and even though Lake Victoria would need a rest from over fishing, it would cause a wide spread famine a region where millions are directly or indirectly depending on the fish from Lake Victoria to survive. Under the suffocating blanket of water hyacinth, dead plant materials began to rotten and foul the drinking water. The water hyacinth also turned out to be a great place for water snails to breed – water snails that harbour the Schistosomiasis (Bilharzias) parasite. In 1995 more than 90 percent of the Ugandan coastline was covered in Eichhornia crassipes. To mechanically control the hyacinth growth seemed hopeless and chemicals such as herbicides would harm not only the Eichhornia crassipes, but the rest of the Lake Victoria ecosystem as well. The problem with water hyacinths was however not restricted to Lake Victoria, water hyacinths had been a problem in the U.S. too since it was introduced from South America in 1884. A vide range of bio-control species had been tested in the U.S. and in 1972 the mottled water hyacinth weevil, Neochetina eichhorniae, was deployed in Florida. It is an insect that feeds on water hyacinth and has a life span of just 90-120 days. Later, weevils with even shorter lifespans were used, such as the Sameodes albiguttalis that has a lifespan no longer than 30 days. Dr. Ogwang, a Ugandan entomologist, performed tests to find out whether these weevils could be used in Lake Victoria as well. He found that they only attacked the water hyacinth and left local crops alone. Dr. Owang introduced weevils to Lake Victoria and the results where great. It is still impossible to determine the long time effects of introducing yet one other species to the Lake Victoria environment, but at least for now it looks as if the battle against the Water Hyacinths has been won without any casualties.
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Christmas Fulu, Haplochromis (Xystichromis) phytophagus
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