Lake Tanganyika

Lake Tanganyika is Africa's longest and deepest lake, about 675 kms long, 70 kms wide, and as much as 1440 meters deep in places. Unlike many of the Rift Valley lakes, which lie in closed drainage basins, Lake Tanganyika has an outlet at Kalemie in Zaire through which water flows to the Atlantic. Thus it has never built up a high concentration of minerals. It contains about 0.4 grams of mineral salts per liter, mostly magnesium carbonate and sodium carbonate, with lesser amounts of potassium chloride and calcium carbonate. It is slightly alkaline (pH 8.5) and its temperature is typically 230C (730F). Although the surface of the lake is often whipped by storms, there is little circulation in its depths. All of the lake's organisms live in the top 200 meter layer, as below that depth there is no oxygen.

A Dagaa fish

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Most of the lake's 250 species of fish are endemic, i.e. they live nowhere else. There are over 200 species of cichlids alone-these are mostly small deep-bodied fish, often brightly colored, and almost all are unique to this lake. There are some large fish as well: Nile perch, tigerfish, yellowbellies and others. But the most economically important fish is the tiny DAGAA (Stolothrissa tanganyikae), a silvery sardine-like fish measuring 10 cms or less. It is related to the marine herring, and originally may have entered the lake via the Zaire river system from the Atlantic. Dagaa eat plankton and live in immense shoals near the surface in open water.

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