Lake Victoria was discovered in 1858 by 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 African rift lakes. The lake is believed to be the most rapidly developing lake in regards to the rapid growth of species numbers with over 200 distinct species developing since it came into existence. In that regards 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 a very rapid rate. There are several theories that scientists have for the rapid depletion of the cichlids. I will cover each briefly in the article.
The first of these reasons is one that for a number of years was believed to be the sole reason or at least the most widely published reason. This reason is the introduction of 2 nonendemic species of fish. In the 1950s, 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 majority of the reason for this decline. The Nile Tilapia on the other hand is a plankton eating fish that may not have had a great effect on the native cichlid population but may also be competing for food with some of the species. These fish were introduced to provide a food source for many countries. They grow much larger than the cichlids that exist in the lake. It is this size combined with the predatory behavior of the Nile Perch that scientists believe was too much for the native populations of cichlids. However, in recent years, scientists have come up with several new theories on what is causing the decline of the native cichlid population.
Another of these new theories has to do with the vast amounts of pollution that are 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 in algae levels in the lake. Pollution providing the necessary nutrients for algae growth. The algae levels are five to ten times the levels of the 1960s. This algae then die off creating more pollution contaminating the lake further. Visibility levels are measured in the lake by measuring the depth at which a white disc is visible under the surface of the water. This test has shown decreasing visibilities from a depth of about five meters in the 1930s 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 die-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. With these algae blooms is an increase in the dangerous blue-green algae causing more disease in the human population. Along with this growth in algae is the development of a water plant called hyacinth. 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 don’t forget the gorgeous cichlids from Lake Victoria and their desperate plight.