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Lake Malawi Biotopes

The huge mass of water as Lake Malawi is, there is found a number of different areas. The initial allocation to 7 types made in 1960 is the most suitable. Knowledge of different types of environments allows the aquarists establish the most natural environment in aquariums.

Coast of the lake is created by three main types: rocky, sandy and marshy. Tectonic structure of faults is base of the coast layout, descent, and the length. Rocky or sandy and sandy-plant shores alternate in the intervals of 110 km. Border cliffs along the edge of break create the rocky shore, while shallow edge of Valley is mainly sandy or sandy with vegetation. A large sandy plateau, river deltas or group of stones interrupt the main site. Rocky sites have a hierarchical structure with sudden spaces of smaller dimensions. The longest uninterrupted part of the rocky coastline is 6.3 km long, north of Ruarwe. Sandy localities extend deeper and continued in a Valley. Some very isolated part of the rocky coast very easily dry out and are therefore temporarily unstable. In such areas, species isolation is difficult and the immigration of other species is very likely. The longest non-rocky part of the coast is 99.5 km long. Each type of coast is inhabited by very different fish communities.

Sandy zones

Although most aquarium fish come from rocky areas, the main part of the coast (about 70%) is created by gradually sloping sandy areas. Mbuna cichlids are rare in these areas, unlike the various "sand cichlids" from group of non-mbuna. Especially Lethrinops, Taeniolethrinops and Tramitichromis species and many representatives of the genus Nyassachromis occur in large numbers over a sandy bottom. Most observations of the sandy coastal communities were made in relatively protected areas such as Nkhata Bay, Cape Maclear, Monkey Bay and Chirombo Bay. During the breeding season, dominant males show a beautiful color and build nests. In such places, so called friction colonies are seen which consist of hundreds of males living side by side in their territories or sand nests. The coloration of fish, the shape of the nest may also be factors that differentiated during evolution between species. However, if these species are not reproducing, they look very similar. They also move along the coast and it is hard to predict their occurrence area. Even in sandy areas dominated Haplochromis types of cichlids in terms of species abundance. In communities which are occurring outside the Nkwichi beaches in Mozambique, tilapias are found mostly. The main species are three species of "chambo" of genus Oreochromis, which mainly feed on crustaceans and microorganisms that are looking for in the sediment or filtered from the water column.

Fishes in this habitat are poorly studied source of fishing on Lake Malawi. Sandy areas are often near rivers, bringing sediments of agricultural water. Sandy littoral (0-15 m) is a temporarily unstable region, depending on the season. In the river Linthipe, 197 kinds of cichlids and other species in total has been caught during 8 months. Haplochromis type cichlids are found in roughly equal numbers in the rainy and dry periods. With distance from the mouth of the river into the lake the number of fish decreases in the dry season, but increases in the rainy season. The opposite tendency is in the non-cichlid fish. Based on the variable climate and turbulent character of these areas, it seems that fish of sandy shore are more mobile than mbuna inhabiting the rocky part of the coast.

Important species among Haplochromis genus is widely occurring omnivore Fossorochromis rostratus, various species of the genus Lethrinops and Taeniolethrinops which sift the sand, Copadichromis feeding a variety of zooplankton and various species feeding on snails (Trematocranus placodon, Chilotilapia rhoadesii). Representative species of predators are Nimbochromis and rarer species such Champsochromis caerulus. Snails are commonly found on the sandy coast, especially in turbid sediment in deeper water. The most remarkable are the large Lanistes snails. Their empty shells create sometimes large areas in deeper water and are populated by specialized mbuna, which reproduce in the shells, as Pseudotropheus livingstoni.


Rocky zones

Rocky coast is the most studied. It does not differ from the sand only visually, but also the number of species is different. It is a major environment of most species caught for aquarium purposes. Overall, rocky regions take only about 5% of the area that is potentially suitable for the fish population. The water is usually crystal clear and fish are not too moving, so they can be well observed. This biotope is inhabited mainly with mbunas. Males and females are sometimes brightly colored and territorial. Most species eat algae on rocks as well as other small organisms in the algae. Along with mbunas, specialized cichlids Protomelas taeniolatus, which feed on algae, Placidochromis milo who has enlarged lips and sucking small invertebrates from rocks, and Nimbochromis linni and Tyrannochromis macrostoma (both are Mbuna predators) live in rocky environments. While mbunas are territorial throughout the year, males of non-mbunas can build territories only during the breeding. Females usually prevent small groups of independently feeding and freely swimming fry, while mbunas cease to care about their fry immediately after releasing from the mouth.


Many species living in sandy areas which include so-called "utaka" (Copadichromis) and "binga" or "liani" (Dimidiochromis kiwinge) reproduce in rocky habitat or in its vicinity. Fish that do not belong to the cichlids represent algae eating "ningwe" (Labeo cylindricus) and predators Mormyrops anguilloides. Among the smallest invertebrates (Ostracoda, Chironomida, Copepoda), it is estimated that at the square meter of rocks surface live to 300 000 individuals in Nkhata Bay. It also includes many insect larvae, beetles. Rock surface is covered with filamentous blue-green algae Calothrix and green algae Cladophora.




Intermediate zones

Areas where the rocks lie on the sand or mud are called transitional zones. The transitional zone is an area that is difficult to define. In many places, the sandy and rocky areas overlap. Except the algae, there is also freely deposited sediment and organisms living in the bottom as food for fish. These biotopes are among the richest habitats for fish. Some mbunas prefer this environment, for example Pseudotropheus lucerna and P. "tropheops". Gephyrochromis lawsi lives in deeper water. Typical fish species in these areas are fish of the genus Aulonocara, which have extended tubules of the side line and especially on the underside of the head. They stand motionless just above the bottom and try to detect the movement of invertebrates in the sediment and then sift the bottom where try to find these organisms. Many males of Aulonocara are beautifully colored. Other species of this genus live in sandy or muddy environments spreading from the coast up into the deeper layers of about 130 m. Other characteristic species of transitional areas are Ctenochromis pictus and Protomelas fenestratus, which has a greater ability to migrate through the sandy bottom at greater distances than P. taeniolatus.

In the aquarium, such miniature transition zone can be build only in large tanks because once cichlids starts feel safe in the aquarium, they are not tied to a particular area and usually reside anywhere. As a protective stone is always very close, mbunas that are fearless, they are able to swim to the sandy area adjacent to be suddenly scared by the male of Nyassachromis from its sand nest.


Other zones

The remaining zones are for hobbyists only minor importance. Open water should be understood differently from the open waters near the coast. This area is often populated with fish that do not belong to the cichlid (Engraulicypris sardella, also known as a Malawian sardine). In open water live also so called Utaka (Copadichromis), but stay close to shore. Imitation of habitat for Copadichromis breeding in captivity would not be difficult, if its size is not so great. The largest possible aquarium with plenty of swimming space and rocky back wall is sufficient. However, most of the imported Copadichromis can be kept in standard aquaria. Although the fishing effort in open water is low, to 200 m from the coast is relatively high. A number of species has been caught in large numbers and because of fewer offspring in cichlids, there is a threat of their extermination. Near Cape Maclear the water is polluted from ships.

These areas may include shallow muddy waters and the deeper crystal clear water. In shallow, muddy water occur species like Lethrinops turneri, L. lethrinus, L. macrochir, Placidochromis longimanus, Otopharynx "argyrosoma red", O. tetrastigma.

A very special habitat lies in the deep water from 30 to 200-250 m. Even deeper water is already contaminated by carbon disulfide, which are conditions for the life of higher organisms impossible. The deep waters inhabit representatives of genera Diplotaxodon, Alticorpus, Pallidochromis and some large Rhamphochromis. Especially tasty Rhamphochromis and Diplotaxodon are often caught at depths around 160 m. None of the species living in deep water are interesting for the aquarium fish keeping.

At depths less than 40 m, the bottom is soft where live Lethrinops stridei, L. christyi and many Mylochromis as M. anaphyrmus. In certain areas dominated layers of snails and most abundant species are Pseudotropheus livingstonii and P. elegans. Predators include species of the genus Buccochromis, Taeniochromis holotaenia and Champsochromis caeruleus.

At depths of 40-75 m, the dominant species are benthophag species like Lethrinops microdon, L. macracanthus and L. longimanus, along with the species feeding on snails, such as L. mylodon and Mylochromis anaphyrmus and species feeding on plants and zooplankton (Copadichromis virginalis). Predators occurring here are Otopharynx speciosus and Sciaenochromis benthicola. Species living in the middle depths like Rhamphochromis and Diplotaxodon limnothrissa occur frequently in fishermen's nets. Fish communities in these depths were seriously affected by hunting and local populations of some species have decreased or completely disappeared.

Haplochromis species living at the bottom having big eyes dominate at depths over 75 m which feed on bottom invertebrates. These include Lethrinops gossei, L. longipinnis and various Alticorpus species that have enlarged lateral line sensory channels, similarly to Aulonocara. There are also a variety of little known and mostly undescribed species belonging to the Aulonocara and Placidochromis. A common predator is Pallidochromis tokolosh, Diplotaxodon, which catches the fish over the bottom and Alticorpus mentale. These depths are relatively low light and with limited light spectrum. It is therefore surprising that there are several species of brightly colored males, for example head of Lethrinops gossei, L. longimanus and L. "deep-water albus" is a metallic blue or green. Alticorpus peterdaviesae has a clear-yellow head and back and some Rhamphochromis males have entire lower half of the body orange. Some species are colored in dark-light contrast. Males Alticorpus mentale have dark fins and bands, while Diplotaxodon are either black or have black and silver color. Many Haplochromis species eat insect larvae.

The last region consists of estuaries and vegetated shoreline. In these areas it is possible to see not only the species that live in rivers mouths (Tilapia, Astatotilapia, Serranochromis), but also representatives of non-mbuna cichlids live here. In the partially protected areas, there are plant vestures on sand plains or among rocks. Bunches of Vallisneria and Ceratophyllum are found in many places and sometimes you can see the long narrow Potamogeton except southern part of the lake. Of the Haplochromis species, Protomelas similis feed on leaves of plants. Other species feed on algae on the leaf surface, for example Hemitilapia oxyrhynchus and Cyathochromis obliquidens. Species such as Placidochromis johnstonii and Protomelas kirkii catch small invertebrates between plants and their roots in the sediment. Dimidiochromis compressiceps is characteristic predator of young fish. The leaves are Vallisneria are site of abundant algae, which are similar to those growing on the rocks and also large shrimp Cardinia nilotica lives here.

The smaller clusters of plants attract fish which are characteristic for marshy areas. Large sections of reed are common in the estuaries, as Senga Bay and water reservoirs, such as Chia lagoon. Reed zone is important for the young fish life of various fish species as a Copadichromis and Rhamphochromis longiceps. However, reed is often removed for better fishing in the bays using the nets. This has the adverse effects on young fish because they are easier to catch for man, but also for predators because they lost their natural shelters. Besides the fry, the fish common in river mouths occur in these areas like Astatotilapia calliptera, Oreochromis shiranus, Tilapia rendalii and Serranochromis robustus. The reed area is also home of predator Dimidiochromis strigatus that occasionally occurs in rivers. Non-cichlid fish are very abundant in these areas. Small barbus and killifish (Aplocheilichthys johnstonii) are common here. Sometimes you can see large shoals of tetras Brycinus imberi. Also, there is much more of invertebrates which are typical for lakes, such as various insect larvae.

Literature

Allison, E.H., Irvine, K., Thompson, A.B. 1996. Lake flies and the deep-water demersal fish community of Lake Malawi. In: J. Fish Biol., 48, 1006-1010.
Eccles, D.H. 1974. An outline of the physical limnology of Lake Malawi (Lake Nyasa). In: Limnol. Oceanography, 19, 730-742.
Herrmann, H.J. 1996. Aqualex. Malawi cichlids. Dahne Verlag GmbH : Germany.
Marsh, B.A., Marsh, A.C., Ribbink, A.J. 1986. Reproductive seasonality in a group of rock-frequenting cichlid fishes in Lake Malawi. In: J. Zool., 209, 9-20.
Pereyra, R., Taylor, M.I., Turner, G.F. et al. 2004. Variation in habitat preference and population structure among three species of lake Malawi cichlid genus Protomelas. In: Mol. Biol., 13, 2691-2697.
Ribbink, A.J., Marsh, B.A., Marsh, A.C. et al. 1983. A preliminary survey of the cichlid fishes of rocky habitats in Lake Malawi. In: South African J. Zool., 18, 149-310.
Robinson, R.L., Ribbink, A.J. 1998. Abundance and seasonality of temporary cichlid breeding territories on a rocky shore in Lake Malawi. In: Ichthyol. Explor. Freshwaters, 8, 299-312.
Thompson, A.B., Allison, E. 1997. Potential yield estimates of unexploited pelagic fish stocks in Lake Malawi. In: Fish. Management Ecol., 4, 31-48. Turner, G.F. 2004 Lake Malawi habitats.http://www.hull.ac.uk/cichlids/Malawi_Habitats.htm
Turner, G.F. 1994. Description of a commercially important pelagic species of the genus Diplotaxodon (Pisces: Cichlidae) from Lake Malawi, Africa. In: J. Fish Biol., 44, 799-807.
Tweddle, D., Lewis, D.S.C., Willoughby, N.G. 1979. The nature of the barrier separating the Lake Malawi and Zambezi fish faunas. In: Ichthyol. Bull. J.L.B., 39, 9.
Vollmer, M.K., Bootsma, H.A., Hecky, R.E. et al. 2005. Deep-water warming trend in Lake Malawi, East Africa. In: Limnol. Oceanogr., 50, 727-732.

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