Lake Victoria was discovered in 1858 by the British explorer John Speke. It is one of the largest lakes in the world covering 26,560 sq miles. As recently as 12,500 years ago the lake was believed to be a grassy plain. This makes it the youngest of the three east african lakes. The lake is believed to be the most rapidly developing lake in regards to the growth of species numbers. It is estimated by some to have developed over 200 distinct species since it came into existence. In that regard, Lake Victoria may be developing species more rapidly than any other animal group in the entire world. With this in mind, it is quite tragic that the native population of cichlids is dwindling down at an alarming rate. There are several theories that scientists have for the rapid depletion of the cichlids. I will cover each briefly in this article.
The first of these reasons is one that for a number of years was believed to be the sole reason, or at least it was the most widely published. This reason is the introduction of 2 non-endemic species of fish. In the 1950ís British colonists introduced the Nile Perch (Lates niloticus) and the Nile Tilapia (Oreochromis niloticus). The Nile Perch is quite a predatory species that is believed to be the predominant cause for this decline. The Nile Tilapia on the other hand is a plankton-eating fish which may not have had a great effect on the native cichlid population. It is however, having an indirect effect inasmuch as it competes for food with some of the cichlid species. These fishes were introduced to provide a food source for the countries around the lake because they grow much larger than the cichlids. It is this size combined with the predatory behavior of the Nile Perch that scientists believe has been the cause for the extinction of so many cichlid species in the lake. However, in recent years, scientists have come up with several new theories on what is causing the decline of the native cichlid populations.
One of these new theories has to do with the vast amounts of pollution that is flowing into the Lake from the surrounding countries. The countries that surround the Lake have undergone a substantial population boom in recent years, vastly increasing the amount of pollution being pumped into the lake. At the present time, oxygen levels at the bottom of the lake are not great enough to support life. Lake Victoria is on the verge of becoming a dead lake. Another part of this theory is that the visibility is so poor that the brightly colored cichlids from the lake are having trouble correctly identifying mates and therefore not mating as often. This pollution is a contributing factor to some of the other problems in the lake.
The next problem is the increase of algae levels in the lake. With the pollution providing the necessary nutrients for algae growth, the algae levels are five to ten times the levels of the 1960ís. This algae then dies off, in turn creating more pollution, further contaminating the lake. Visibility levels are measured in the lake by measuring the depth at which a white disc is visible under the water's surface. This test has shown decreasing visibilities from a depth of about five meters in the 1930ís to a depth of one meter or less in 1990. As you can see this is a serious danger to the lake. As pollution levels go up, algae growth goes up. In turn the algae that dies off creates more pollution in an apparent never-ending cycle of lake destruction. This is even having a great impact on the local populations around Lake Victoria. Along with these algal blooms is an increase in the dangerous blue-green algae which has causes disease in the human population. In addition to the prevalence of algal blooms, a noxious plant called hyacinth has developed. This plant was unseen until 1989 and since then has exploded to choke out harbors and coves.
As you can see the situation is dire. So in your cichlid keeping experience, please donít forget the gorgeous cichlids from Lake Victoria and their desperate plight. □