The Great Lakes of East Africa
by Marc Elieson
This article has the purpose of introducing you to the three great lakes of east Africa: Lakes Victoria, Malawi, and Tanganyika.
These three lakes are in eastern Africa, nestled in and around what is known as Africas Great Rift Valley. This depression extends for more than 3,000 miles, beginning in Syria and traveling through southwestern Asia before it enters into southeastern Africa. This valley is anywhere from 18 to 60 miles wide, and ranges in elevation from 1,300 feet below sea level to 6,000 feet. This valley contains some of Africas most spectacular scenery, being flanked by volcanoes and mountains, including Mt. Kilimanjaro, the highest peak in Africa, at 19,340 feet.
The Great Rift Valley was formed some 25 million years as Africa and Eurasia collided, which caused the earths crust in eastern Africa to drop while the two recoiling twin faults pulled apart. The effect has been likened to the keystone of an arch dropping as the side pillars collapse.
In eastern Africa the valley separates into two branches: the Eastern Rift and the Western Rift. The Eastern Rift, or main section of the valley, cuts across Ethiopia and then south across Kenya, Tanzania, and Malawi to Mozambique. Lake Malawi lies in the Eastern Rift branch. Just north of Lake Malawi is the western branch, which runs north along the eastern border of Zaire.
Within this branch of the Great Rift Valley are Lake Tanganyika and several other smaller lakes, including Lakes Edward and Albert. Lake Victoria does not lie in the Great Rift Valley but between its main and western branches.
Also known as Victoria Nyanza, Lake Victoria is bordered by Uganda, Kenya, and Tanzania. It has an area of 26,830 square miles (the size of Ireland), and is 250 miles long at its greatest width, making it the worlds second largest freshwater lake, after Lake Superior. It also has an average depth of 120 feet, with its deepest point reaching 250 feet. Lake Victoria receives its water from many rivers, the largest being the Kagera. The lake then drains into the Nile through Owen Falls, where there is a man-made hydroelectric dam. Of note, Lake Victoria is the youngest of the three rift lakes.
Lake Victoria was once home to more than 500 different species of haplochromine Cichlids before Nile perch were introduced to the lake by the lakes residents. Introduced in the 1950s to provide food for the people of the lake and develop commercial fishery, these predators grow up to 6 feet long, and have successfully wiped out some 250 of these 500 Cichlid species. The diversity of species is incredible when you realize that all of western Europe hosts only around 60 species of freshwater fish. Even more astonishing is that it's believed that all of these different species evolved from a single progenitor: Astatotilapia nubile
It should also be noted that there are no extreme types of Victorian Cichlids that are not connected by a number of intermediate species. This has made classifying and grouping these fish extremely difficult for taxonomists. Con-sequently, more than 95% of the Cichlid species endemic to Lake Victoria belong to the old generic genus Haplochromis. Despite their default classification as all belonging to one large genus, very few generalizations can be made. One of the generalizations that is safe to make is that all but one species are maternal mouthbrooders. Also, these species are best kept in groups, not pairs.
The water in Lake Victoria is much less clear than that in Lakes Malawi and Tanganyika. Transparency has been measured between less than 4 and 10 feet in inshore areas. The pH is alkaline, ranging from 7.2 to 8.6, and carbonate hardness is between 2 and 8 dH. The temperature can be as low as 70 degrees at the surface during the dry season and reaches 81 degrees during the wet season. Interestingly, it receives more rainfall (about 200 to 250 centimeters a year) in the middle than anywhere near its edges. Some biotopes of the lake resemble those of Lake Malawi, with lots of large rocks (see photo).
Lake Malawi, known locally as Lake Nyasa, is the ninth largest lake in the world and lies between the countries of Malawi on the west and Tanzania and Mozambique on the east. It is 360 miles long and 25 miles wide, with an approximate area of 8,683 sq mi, and reaches depths of 2,300 feet. The lake has a visibility of up to 70 feet.
Lake Malawi contains a greater variety of indigenous species of Cichlid fishes than any other lake in the world. World Wildlife Fund researchers have identified over 500 species to date that are not found anywhere else in the world. That is more than all of the freshwater species found in all the waters of both Europe and North America. The Cichlids of Lake Malawi, perhaps even more so than the Cichlids from the other two rift lakes, are brightly colored and patterned. For this reason, they have been a big hit with aquarists all over the world.
Among these popular Cichlids are the Mbuna and the Haps.
The Mbuna (i.e., rock-dwelling fish) are a large group of Cichlids that live among large piles of rocks along the shoreline. They are usually seen in large groups, but are by no means a schooling fish. In some areas of Lake Malawi, 20 fish per square meter is not uncommon. Both sexes of the more than 100 species of Mbuna are unusually colorful, whereas typically, only males have color. They are very colorful with bright patterns of horizontal stripes or vertical bars. Mbuna are smaller and tend to have flat faces, which enables them to better scrape algae from rocks. These consist mostly of, but not limited to, the genera Pseudotropheus
Haps, for want of a better name, are basically a non-Mbuna flock that are informally called Haps because many of these fish once belonged to the broad genus Haplochromis Hilgendorf.
Most Haps are piscivores, unlike the vegetarian Mbuna. There are some exceptions to this generalization, however, but these do well on a piscovore's diet nonetheless. Haps are aggressive, but not as aggressive as the vegetarian Mbuna. They have long, slender, almost torpedo-like bodies, and cruise the open water. Most of these fish are silver or gray when small, and the males become very brightly colored as they mature. Females typically remain without color. For more information on Haps and Mbuna, see Haps Vs. Mbuna
The water chemistry in Lake Malawi is very similar to that of Lake Victoria. For this reason, many species from these two lakes can be housed together. Lake Malawi's pH ranges from 7.8 to 8.6, with a total hardness of 4.0-6.0 dH. The reason for the variation is caused by the level of Carbon Dioxide dissolved in the water. In areas with turbulent water, where the water is better aerated, the pH is higher, while in calm bays, the level of dissolved Carbon Dioxide is higher; consequently, the pH is lower there. Surface temperature ranges from 76 to 85 degrees, while the temperature at lower levels of the lake remain at a constant 70 degrees. Carbonate hardness ranges from 6.0 to 8.0.
About one third of the coast is rocky, which is home to the mbunas. The remaining shoreline is characterized by sandy beaches and bottoms. This is where most of the open-water Haps and peacocks dwell. A few Cichlid species inhabit the muddy and weed-strewn bottom where larger rivers flow into the lake. The shores of the lake are generally sandy, and the resort areas are generally bilharzias free. Lake Malawi is unusual in that it does not have tides or currents.
Lake Tanganyika is the longest lake in the world, boasting a length of 420 miles, and is the second deepest in the world, reaching a depth of 4,710 feet. It is the second largest lake in Africa, after Lake Victoria, covering about 12,700 square miles. At its widest point it is 45 miles wide. It is bordered on the east by Tanzania, on the north by Burundi, on the west by the Democratic Republic of the Congo (formerly Zaïre), and on the south by Zambia. Lake Tanganyikas only outlet is the Lukuga River, which flows into the Congo River.
As a result of having just one outlet, this rift lake has a particularly high mineral content. This is because most of the salts that flow into it don't leave, but rather get left behind as the water evaporates.
The water chemistry of Lake Tanganyika, is much more alkaline and hard than is the water from Lakes Malawi and Victoria. Its pH levels range from 8.6 to 9.5, with a total hardness of 11-17 dH, and carbonate hardness being between 16 and 19 dH. The water in the lake is very clear, with visibility up to 70 feet. In the upper 130 feet, the water is oxygen-rich. This is an important point to consider when caring for Tanganyikans in captivity. Their water should be as close to saturation as possible. Surface temperature ranges from 76 to 82 degrees, while the temperature at lower levels of the lake remain at a constant 70 degrees. It is important to keep the temperature of the water within this range, as water with a temperature higher than 84 degrees can be lethal to Tanganyikans. This is because as the temperature increases, their metabolism speeds up, and their demand for oxygen increases with it. At 85 degrees the oxygen content must be near saturation of they will die of suffocation.
The lake is known for its many varieties of fish, of which are almost 200 unique Cichlid species. Crocodiles and hippopotamuses are often found on the shores of the lake. The biotope of the lake is sandy, and therefore, these fish are best kept in an aquarium with sand, not gravel. This is especially true of the sand-dwelling species. Many of the Tanganyikan species are small and can be housed in 10 and 20-gallon aquariums, such as the shell-dwelling genera Neolamprologus