Lake Tanganyika Sardine – Biology, History, and Fisheries

Lake Tanganyika Sardine (Limnothrissa miodon) is a group of freshwater fish in the family Clupeidae of Lake Tanganyika origin but today it is found in other lakes in Africa as a source of food. It contains only one immediate subordinate within the genus Limnothrissa. This sardine together with Lake Tanganyika Sprat are all known as Kapenta.

Freshwater Sardines Lake Tanganyika Distribution

The name speaks for itself, Lake Tanganyika Sardine is originated in Lake Tanganyika, scattered throughout the lower branches of the Malagarasi River. They are also found in Lake Kivu in Rwanda and Lake Kariba in the Zambezi Basin between Zambia and Zimbabwe. And more recently in the Itezhi-Tezhi dam in Zambia. They have taken over Lake Kahora bassa in Mozambique from Lake Kariba. The migratory fish have managed to live through power plants blades in the Kariba dam and have taken control of Lake Cahora bassa through small rivers.

Description

The most common fish, this is a small silver fish with a bright line on its side, a wide nose with narrowing sides. It has large air bladders that allow it to swim long distances by diving deep in column of water. It can reach to a height of up to 17 centimeters (6.3 countries) but most of its studied population is about 10 centimeters (3.9 inches) and becomes fully matured at 6.8 centimeters (2.7 inches).

Biology

Lake Tanganyika Sardine migrate by swimming above and below the water, spending the day on the narrow shores in the shallow water. climbing back up to the surface of the water in the evening scattered around on the open waters, although on the lake Kivu the fish comes up the surface in early mornings and late afternoons. It is thought that these cycles are basing on the food sources, heterotrophic plankton, but not in Lake Kariba. It seems that Lake Tanganyika Sardine and heterotrophic planktons respond to the same type of effects which means that they occur in a certain area at the same time. One speculation is that may be a response to intensity of light or a defense mechanism against enemies, which has similarity with what has been seen in marine clupeids.

Thermocline depth and dissolved oxygen amount determine the depth used by Lake Tanganyika Sardine. Under the thermocline, the water is usually anoxic and starting November to April, the fish are usually found no deeper than 20 meters (66 feet). Larger fish migrate to deeper waters as they increase their size. With young fish preferring to swim in fresh water up to 1.5 meters deep (4.11 feet) on rocky or sandy bottoms and areas with steep coastal areas. Larger fish go to areas with shorter depths for reproduction. This is always in the rainy season around May and June where it reaches the maximum and starts again in December and January but has been explored to occur throughout the whole year. Fish breeding increases as they grow; in specimens collected from Lake Kariba fish that was 46 millimeters (1.8 inches) in length contained 600 eggs but a different one with dimensions of 11.4 centimeters (4.5 inches) had 14,044 eggs. In Lake Tanganyika fish had higher number of ova that could likely be laid and a specimen tested there which was about 140 millimeters (5.5 inches) had 55,000 eggs. The main season for reproduction in Lake Kariba is usually between September to February, the population will overall grow gradually beginning February to August and later declines due to high mortality and a drop in recruitment.

Lake Tanganyika sardine is omnivorousi, generally eats zooplankton and phytoplankton. Studies conducted at Lake Kariba for some time now show that the fish take advantage of the opportunity to eat their prey for a while and various studies show that the main prey are Bosmina longirostris, Mesocyclops spp and Ceriodaphnia dubia. Lake Tanganyika Sardine may have caused a significant decline in aquatic species such as e.g. Diaptomus, Ceriodaphnia and Diaphanosoma which were available in large quantities at Lake Kariba before 1972 but there is insufficient information at the time of sampling what caused their decline. In Lake Tanganyika the prey is recorded as atyid shrimps, copepodsi and prawns but large fish have been known to prey on Tanganyika sprat larva. Other foods include insects that are chironomids, ephemeroptera, trichoptera and hemiptera and some samples from Lake Kariba which in total makes up 55% of the content from stomachs tested and it is shown by these samples that the prey are caught at night on the water surface. In Lake Kivu cannibalism is found to be normal and it is speculated to have a large presence in Lake Kariba but these may also prey on other species of fish, unidentified fish have continued to be recorded in samples of Lake Kariba and examples of southern mouth-brooder called Pseudocrenilabrus philander has been found in 6.4 centimeters (2.5 countries) in Lake Kariba stomach samples.

History of Evolution

A large number of clupeids are marine and Lake Tanganyika originated in the East African Rift Valley and has never been in contact with the sea, the small fish family of Lake Tanganyika Sardine and its relative Lake Tanganyika Sprat are members of the Pellonulinae who are popularly found in the West and South of Africa, for example Microthrissa royauxi and Potamothrissa acuitirostris in the Congo Basin. The rebuilding of Molecular phylogenetic shows that native freshwater Pellonulines dominated West Africa 25 to 50 million years ago, at the end of maritime invasion in the region. Pellonuline herring overtime became distinct in a rapid increase from West Africa, scattered across the African continent and ended up dominating Lake Tanganyika in the early days of its formation. This shows that although Lake Tanganyika has no direct connection with the sea, the origin of these freshwater clupeids was due to the fish emerging from the evolution of ancient marine invasion.

Scientific Name Etymology

The name is derived from the Greek word Limno that means Lake, referring to the division of the Lake Tanganyika fish population; and thrissa is a Greek word for anchovy type that is being used here as a clupeid suffix, the particular name miodoi is a combination of the word mio which means small or less and odoni which means tooth, referring to smaller teeth when in comparison with the Pellonula vorax fish community.

Predators

In Lake Kariba Hydrocynus vittatus is a vital predator on Lake Tanganyika, and its abundance in Lake Kariba increased after sardines got introduced. H. Vittatus’ diet varied by at least 70% of the seafood consumed by H.vittatus including of Sardines up to year 1971. Predators of H.vittatus are often seen in the early hours of the morning and in the evening when they are seen eating Sardines over the lake at that time window.

Other Lake Tanganyika sardine predators in Lake Kariba include Coptodon rendalli, Synodontis zambezensis and Schilbe intermedius. Some birds also consume sardines in Lake Kariba and other places, especially white-winged black tern, Chlidonias leucoptera and the pied kingfisher Ceryle rudis.

Fisheries

In Lake Kariba 360,000 Lake Tangayika sardines were permitted by the Zambian government in 1967 and 1968 to be fished. Here they began to be harvested at a height of 40 mm (1.6 countries) at 3-4 months of age. Most were harvested at a height of 40–50 mm (1.6–2.0 mm) and five months old. It turned out that there was a link between biomass and fishing efforts, since biomass was less than ten percent in 1985 than it was in 1974 when Sardine fishing in Lake Tanganyika started. The annual fish harvest in Lake Kariba ranges from 20,000 to 30,000 tons ((22,000 and 33,000 Few Tons).

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