Lake Tanganyika

thumb|Lake Tanganyika eastern shore in Kagongo Ward, [[Kigoma Region, Tanzania]]

Lake Tanganyika ( ; ) is an African Great Lake. It is the world's second-largest freshwater lake by volume and the second deepest, in both cases after Lake Baikal in Siberia. It is the world's longest freshwater lake. The lake is shared among four countries—Tanzania, the Democratic Republic of the Congo (the DRC), Burundi, and Zambia—with Tanzania (46%) and the DRC (40%) possessing the majority of the lake. It drains via the Lukuga River into the Congo River system, which ultimately discharges at Banana, Democratic Republic of the Congo into the Atlantic Ocean.

The major river flowing into the lake is the Ruzizi River, formed about 10,000 years ago, which enters the north of the lake from Lake Kivu. The Malagarasi River, which is Tanzania's second largest river, enters the east side of Lake Tanganyika.

Lake Tanganyika is an ancient lake, one of only twenty more than a million years old. Its three basins, which in periods with much lower water levels were separate lakes, are of different ages. The central began to form 9–12 million years ago (Mya), the northern 7–8 Mya and the southern 2–4 Mya.

Water characteristics

thumb|Clear water lake of Lake Tanganyika in Kagongo Ward, Kigoma Region, Tanzania

The lake's water is alkaline with a pH around 9 at depths of . Below this, it is around 8.7, gradually decreasing to 8.3–8.5 in the deepest parts of Tanganyika. At depths greater than , the temperature is very stable at . The water has gradually warmed since the 19th century and this has accelerated with global warming since the 1950s.

The lake is stratified and seasonal mixing generally does not extend beyond depths of . As a consequence of the stratification, the deep sections contain "fossil water". This also means it has no oxygen (it is anoxic) in the deeper parts, essentially limiting fish and other aerobic organisms to the upper part. Some geographical variations are seen in this limit, but it is typically at depths around in the northern part of the lake and in the south. The oxygen-devoid deepest sections contain high levels of toxic hydrogen sulfide and are essentially lifeless,

Biology

Reptiles

Lake Tanganyika and its associated wetlands are home to Nile crocodiles (including famous giant Gustave), Zambian hinged terrapins, serrated hinged terrapins, and pan hinged terrapins (last species not in the lake itself, but in adjacent lagoons). Storm's water cobra, a threatened subspecies of banded water cobra that feeds mainly on fish, is only found in Lake Tanganyika, where it prefers rocky shores.

Cichlid fishes

thumb|A biologist collecting samples in 2020 in the murky waters of Lake Tanganyika for a study on the diet adaptations of cichlid fishes to better understand their evolution and speciation.

thumb|One of the many Tanganyika cichlids is [[Neolamprologus brichardi. The complex behaviors of this species and its close relative N. pulcher have been studied in detail]]

Lake Tanganyika is home to at least 250 endemic species of cichlids, and undescribed species likely remain to be discovered. Almost all (roughly 98%) of the lake's cichlid species are found solely there, and nowhere else, thus making it a precious biological resource for the study of speciation and evolution. The cichlids of the African Great Lakes, including Tanganyika, represent the most diverse extent of adaptive radiation in vertebrates. its cichlids are the most morphologically and genetically diverse. This is linked to the maturity of Tanganyika, as it is far older than the other lakes. Tanganyika has the largest number of endemic cichlid genera of all African lakes. Others have proposed splitting the Tanganyika cichlids into as many as 12–16 tribes (Bathybatini, Benthochromini, Boulengerochromini, Cyphotilapiini, Eretmodini, Greenwoodochromini, Perissodini and Trematocarini, in addition to the aforementioned tribes). Trematocara species have, exceptionally, been found at more than , which is deeper than any other cichlid known. Some of the deepwater genera (e.g., Bathybates, Gnathochromis, Hemibates and Xenochromis) have been caught in places virtually devoid of oxygen, and how they are able to survive there is unclear. No Tanganyika cichlids are truly pelagic and offshore, except for some of the piscivorous Bathybates. The fishes' breeding behavior falls into two main groups: the substrate- or sand-spawners (often in caves or rock crevices) and the mouthbrooders. Among the endemic species are two of the world's smallest cichlids, Neolamprologus multifasciatus and N. similis (both shell dwellers), measuring up to , and one of the largest, the giant cichlid (Boulengerochromis microlepis) at up to .

Many cichlids from Lake Tanganyika, such as species from the genera Altolamprologus, Cyprichromis, Eretmodus, Julidochromis, Lamprologus, Neolamprologus, Tropheus and Xenotilapia, are popular aquarium fish due to their bright colors and patterns, and interesting behaviors.

File:Bathybates ferox.jpg|Bathybatini (E): Bathybates ferox is benthic and piscivorous, but the genus also includes pelagic species.

File:Benthochromis tricoti.jpg|Benthochromini (E): Benthochromis horii was scientifically described in 2008, but has often been misidentifed as B. tricoti

File:DKoehl Boulengerochromis microlepis.jpg|Boulengerochromini (E): Boulengerochromis microlepis is one of the world's largest cichlids

File:Kleinschuppiger Kaerpflingsbuntbarsch Cyprichromis microlepidotus Tierpark Hellabrunn-1.jpg|Cyprichromini (E): Cyprichromis microlepidotus and other members of this tribe are open-water planktivores

File:Ophthalmotilapia nasuta Kipili.jpg|Ectodini (E): Ophthalmotilapia nasuta (male) is sexually dimorphic, males being more colorful with longer fins and nose

File:Eretmodus-sp-kavala1.jpg|Eretmodini (E): Eretmodus cyanostictus lives near the bottom in the turbulent, coastal surf zone, like other members of its tribe

File:Schachbrett-Schlankcichlide.jpg|Lamprologini (E): Julidochromis marlieri is popular in the aquarium trade where members of the genus are known as "Julies"

File:Gnathochromis premaxillaris.jpg|Limnochromini (E): Gnathochromis permaxillaris is a zooplanktivore with an unusual protractile mouth

File:Perissodus microlepis juvenile in aquarium.jpg|Perissodini (E): Perissodus microlepis, a specialized scale-eating species

File:Oreochromis tanganicae (Günther).jpg|Tilapiini: Oreochromis tanganicae is one of the most common coastal species found in local fish markets

File:TropheusspRed200.jpg|Tropheini (E): Tropheus moorii ("red" Chimba morph) is highly variable and the taxonomy of some of the morphs is questionable

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Other fish

thumb|The [[Tanganyika killifish (Lamprichthys tanganicanus) is the only member of its genus]]

Lake Tanganyika is home to more than 80 species of non-cichlid fish and about 60% of these are endemic.

The open waters of the pelagic zone are dominated by four non-cichlid species: Two species of "Tanganyika sardine" (Limnothrissa miodon and Stolothrissa tanganicae) form the largest biomass of fish in this zone, and they are important prey for the forktail lates (Lates microlepis) and sleek lates (L. stappersii). and S. multipunctatus. The facultative brood parasites often lay their eggs synchronously with mouthbrooding cichlids. The cichlid pick up the eggs in their mouth as if they were their own. Once the catfish eggs hatch the young eat the cichlid eggs. Although not endemic on a genus level, six species of Chrysichthys catfish are only found in the Tanganyika basin where they live both in shallow and relatively deep waters; Although other African Great Lakes have Synodontis catfish, endemic catfish genera and Mastacembelus spiny eels, the relatively high diversity is unique to Tanganyika, which likely is related to its old age. Among the endemic bivalves are three monotypic genera: Grandidieria burtoni, Pseudospatha tanganyicensis and Brazzaea anceyi. All the Tanganyika thalassoids, which are part of Prosobranchia, are endemic to the lake. A total of 17 freshwater snail genera are endemic to the lake, such as Hirthia, Lavigeria, Paramelania, Reymondia, Spekia, Stanleya, Tanganyicia and Tiphobia.

Crustaceans are also highly diverse in Tanganyika with more than 200 species, of which more than half are endemic. at least 11 species of small atyid shrimp (Atyella, Caridella and Limnocaridina), an endemic palaemonid shrimp (Macrobrachium moorei), about 100 ostracods, including many endemics, and several copepods. Among these, Limnocaridina iridinae lives inside the mantle cavity of the unionid mussel Pleiodon spekei, making it one of only two known commensal species of freshwater shrimp (the other is the sponge-living Caridina spongicola from Lake Towuti, Indonesia).

Among Rift Valley lakes, Lake Tanganyika far surpasses all others in terms of crustacean and freshwater snail richness (both in total number of species and number of endemics). For example, the only other Rift Valley lake with endemic freshwater crabs are Lake Kivu and Lake Victoria with two species each.

Other invertebrates

The diversity of other invertebrate groups in Lake Tanganyika is often not well-known, but there are at least 20 described species of leeches (12 endemics), 9 sponges (7 endemic), 6 bryozoa (2 endemic), 11 flatworms (7 endemic), 20 nematodes (7 endemic), 28 annelids (17 endemic)

Fishing

thumb|Fishing Boat in Kagongo Ward, Kigoma District

thumb|200px|right|Fishermen on Lake Tanganyika

Lake Tanganyika supports a major fishery, which, depending on source, provides 25–40% or 60% of the animal protein in the diet of the people living in the region.

Lake Tanganyika fish can be found exported throughout East Africa. Major commercial fishing began in the mid-1950s and has, together with global warming, had a heavy impact on the fish populations, causing significant declines.

There are many methods which the native people of the area used for fishing. Most of them included using a lantern as a lure for fish that are attracted to light. There were three basic forms. One called Lusenga which is a wide net used by one person from a canoe. The second one is using a lift net. This was done by dropping a net deep below the boat using two parallel canoes and then simultaneously pulling it up. The third is called Chiromila which consisted of three canoes. One canoe was stationary with a lantern while another canoe holds one end of the net and the other circles the stationary one to meet up with the net.

The first known Westerners to find the lake were the British explorers Richard Burton and John Speke, in 1858. They located it while searching for the source of the Nile River. Speke continued and found the actual source, Lake Victoria. Later David Livingstone passed by the lake. He noted the name "Liemba" for its southern part, a word probably from the Fipa language. Tanganyika means "stars" in the Luvale language.

The lake was the scene of Battle for Lake Tanganyika during World War I. With the aid of the Graf Goetzen, the Germans had complete control of the lake in the early stages of the war. The ship was used both to ferry cargo and personnel across the lake, and as a base from which to launch surprise attacks on Allied troops. It therefore became essential for the Allied forces to gain control of the lake themselves. Under the command of Lieutenant Commander Geoffrey Spicer-Simson the British Royal Navy achieved the monumental task of bringing two armed motor boats HMS Mimi and HMS Toutou from England to the lake by rail, road and river to Albertville (since renamed Kalemie in 1971) on the western shore of Lake Tanganyika. The two boats waited until December 1915, and mounted a surprise attack on the Germans, with the capture of the gunboat Kingani. Another German vessel, the Hedwig, was sunk in February 1916, leaving the Götzen as the only German vessel remaining to control the lake.