Oreochromis lidole
Encyclopedia
Oreochromis lidole is a species of fish
in the Cichlidae family. It is found in Malawi
, Mozambique
, and Tanzania
. Its natural habitat
s are river
s and freshwater lake
s.
Oreochromis lidole is a tilapiine cichlid
fish, a member of a group that includes some of the major freshwater food fish species known as 'tilapias
'. This species is found only in and around Lake Malawi
(also known as Lake Nyasa), where it forms part of a complex of similar and closely related species believed to have diversified within the lake.
The species was described as Tilapia lidole in 1941 by the British ichthyologist Ethelwynn Trewavas, from specimens she had collected on a fishery survey of Lake Malawi in 1939. She reported that the name was derived from the local name 'dole', although it was also known as 'galamula' or 'lolo', or more generally as 'chambo' along with similar tilapia species. Along with other mouthbrooding tilapia species, it was reclassified in the genus Sarotherodon in 1976, and later moved into the genus Oreochromis, along with other species showing clear sexual dimorphism (differences in size, shape and colour between the sexes). It has also been included in the subgenus Nyasalapia along with other species where the males develop long, branching genital papillae.
Juveniles of the various 'chambo' species are essentially indistinguishable from one another, but collectively can be identified by their silvery body, tapering vertical bars and 'tilapia spot' on the lower part of the soft rayed part of the dorsal fin. Oreochromis lidole can distinguished from other closely related 'chambo' species at lengths of about 17-20cm or greater, as it generally assumes a big-headed, skinny appearance, resulting from its shallower body, larger mouth and bigger opercular plates (gill-covers). The jaw teeth are set in a 3-4 clearly separated rows, whereas other species often have more or less regularly spaced rows. Dissection can reveal the long, slender lower pharyngeal bone with very slender toothed areas. During the breeding seasons, males become jet black, with white margins to the unpaired fins, which is similar to those of O. karongae, but enables them to be distinguished from those of O. squamipinnis.
Like all other known Oreochromis, O. lidole is a maternal mouthbrooder
: females carry the eggs and small juveniles in their mouths for several weeks. When juveniles have absorbed their yolk sacs, they are released to forage independently, under the female's guard, but are allowed to return to their mother's mouth when danger threatens. Females produce up to 700 young and have been recorded to guard fry up to 5cm long. Breeding mainly occurs during the hot season from October to January, when males gather in deep water (mainly 20-45m) off clean, steeply shelving beaches to dig huge craters (1-3m in diameter) in which courtship and spawning takes place. Females often migrate to more productive turbid waters to release their young, in areas such as Lake Malombe.
Oreochromis lidole feeds mainly on plankton- including crustaceans, such as Bosmina and Diaptomus, diatoms
such as Aulacoseira and Surirella and other larger algae.
Oreochromis lidole has been recorded from throughout Lake Malawi, where it tends to live in deeper, less muddy habitats than related chambo species, although they are often found together in the same fisherman's catch, suggesting they may shoal together. Like other chambo, they are rarely caught deeper than around 50m. Juveniles and brooding females tend to be found in shallower, muddier water, in places such as Lake Malombe. The species was reportedly most common in the productive southern arms of the lake, and rare off muddy or rocky coasts. The species is also reported to occur in a couple of crater lakes just to the north of Lake Malawi, in Tanzania.
Some specimens reportedly collected from Lake Tschungruru in Tanzania were identified as O. lidole by Trewavas. This lake appears to be the Kiungululu Crater (9°18′24.06″S 33°51′54.31″E), which is situated at an altitude of around 450m above the present surface of Lake Malawi. How they got there is a mystery. Some of these fish were sexually mature at sizes of 14-17cm, which is much smaller than mature fish in Lake Malawi. Subsequently, smallish mature specimens were also collected from Lake Kingiri, which is only about 50m higher up than the main lake (9°25′07.67"S 33°51′29.29″E).
Oreochromis lidole was formerly an important food fish on Lake Malawi. It was particularly abundant in the catches of trawlers operating in the South Eastern Arm from Maldeco. Populations of all chambo species declined drastically in the 1990s, but O.lidole appears to have been hardest hit, and on recent surveys was extremely uncommon. The IUCN red listing as 'Endangered' seems justified and indeed may be overoptimistic. The status of the Tanzanian Crater lake populations is unknown.
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
in the Cichlidae family. It is found in Malawi
Malawi
The Republic of Malawi is a landlocked country in southeast Africa that was formerly known as Nyasaland. It is bordered by Zambia to the northwest, Tanzania to the northeast, and Mozambique on the east, south and west. The country is separated from Tanzania and Mozambique by Lake Malawi. Its size...
, Mozambique
Mozambique
Mozambique, officially the Republic of Mozambique , is a country in southeastern Africa bordered by the Indian Ocean to the east, Tanzania to the north, Malawi and Zambia to the northwest, Zimbabwe to the west and Swaziland and South Africa to the southwest...
, and Tanzania
Tanzania
The United Republic of Tanzania is a country in East Africa bordered by Kenya and Uganda to the north, Rwanda, Burundi, and the Democratic Republic of the Congo to the west, and Zambia, Malawi, and Mozambique to the south. The country's eastern borders lie on the Indian Ocean.Tanzania is a state...
. Its natural habitat
Habitat
* Habitat , a place where a species lives and grows*Human habitat, a place where humans live, work or play** Space habitat, a space station intended as a permanent settlement...
s are river
River
A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including...
s and freshwater lake
Lake
A lake is a body of relatively still fresh or salt water of considerable size, localized in a basin, that is surrounded by land. Lakes are inland and not part of the ocean and therefore are distinct from lagoons, and are larger and deeper than ponds. Lakes can be contrasted with rivers or streams,...
s.
Oreochromis lidole is a tilapiine cichlid
Tilapiine cichlid
The Tilapiini is a tribe within the family Cichlidae commonly known as tilapiine cichlids. Most of the taxa herein are called "tilapias", a diverse and economically important group containing the genera Oreochromis, Sarotherodon and Tilapia. A number of smaller genera, such as Alcolapia, Danakilia,...
fish, a member of a group that includes some of the major freshwater food fish species known as 'tilapias
Tilapia
Tilapia , is the common name for nearly a hundred species of cichlid fish from the tilapiine cichlid tribe. Tilapia inhabit a variety of fresh water habitats, including shallow streams, ponds, rivers and lakes. Historically, they have been of major importance in artisan fishing in Africa and the...
'. This species is found only in and around Lake Malawi
Lake Malawi
Lake Malawi , is an African Great Lake and the southernmost lake in the Great Rift Valley system of East Africa. This lake, the third largest in Africa and the eighth largest lake in the world, is located between Malawi, Mozambique, and Tanzania...
(also known as Lake Nyasa), where it forms part of a complex of similar and closely related species believed to have diversified within the lake.
Names
The species was described as Tilapia lidole in 1941 by the British ichthyologist Ethelwynn Trewavas, from specimens she had collected on a fishery survey of Lake Malawi in 1939. She reported that the name was derived from the local name 'dole', although it was also known as 'galamula' or 'lolo', or more generally as 'chambo' along with similar tilapia species. Along with other mouthbrooding tilapia species, it was reclassified in the genus Sarotherodon in 1976, and later moved into the genus Oreochromis, along with other species showing clear sexual dimorphism (differences in size, shape and colour between the sexes). It has also been included in the subgenus Nyasalapia along with other species where the males develop long, branching genital papillae.
Distinguishing Features
Juveniles of the various 'chambo' species are essentially indistinguishable from one another, but collectively can be identified by their silvery body, tapering vertical bars and 'tilapia spot' on the lower part of the soft rayed part of the dorsal fin. Oreochromis lidole can distinguished from other closely related 'chambo' species at lengths of about 17-20cm or greater, as it generally assumes a big-headed, skinny appearance, resulting from its shallower body, larger mouth and bigger opercular plates (gill-covers). The jaw teeth are set in a 3-4 clearly separated rows, whereas other species often have more or less regularly spaced rows. Dissection can reveal the long, slender lower pharyngeal bone with very slender toothed areas. During the breeding seasons, males become jet black, with white margins to the unpaired fins, which is similar to those of O. karongae, but enables them to be distinguished from those of O. squamipinnis.
Reproductive Biology
Like all other known Oreochromis, O. lidole is a maternal mouthbrooder
Mouthbrooder
Mouthbrooding, also known as oral incubation and buccal incubation, is the care given by some groups of animals to their offspring by holding them in the mouth of the parent for extended periods of time. Although mouthbrooding is performed by a variety of different animals, most notably Darwin's...
: females carry the eggs and small juveniles in their mouths for several weeks. When juveniles have absorbed their yolk sacs, they are released to forage independently, under the female's guard, but are allowed to return to their mother's mouth when danger threatens. Females produce up to 700 young and have been recorded to guard fry up to 5cm long. Breeding mainly occurs during the hot season from October to January, when males gather in deep water (mainly 20-45m) off clean, steeply shelving beaches to dig huge craters (1-3m in diameter) in which courtship and spawning takes place. Females often migrate to more productive turbid waters to release their young, in areas such as Lake Malombe.
Diet
Oreochromis lidole feeds mainly on plankton- including crustaceans, such as Bosmina and Diaptomus, diatoms
Diatom
Diatoms are a major group of algae, and are one of the most common types of phytoplankton. Most diatoms are unicellular, although they can exist as colonies in the shape of filaments or ribbons , fans , zigzags , or stellate colonies . Diatoms are producers within the food chain...
such as Aulacoseira and Surirella and other larger algae.
Distribution
Oreochromis lidole has been recorded from throughout Lake Malawi, where it tends to live in deeper, less muddy habitats than related chambo species, although they are often found together in the same fisherman's catch, suggesting they may shoal together. Like other chambo, they are rarely caught deeper than around 50m. Juveniles and brooding females tend to be found in shallower, muddier water, in places such as Lake Malombe. The species was reportedly most common in the productive southern arms of the lake, and rare off muddy or rocky coasts. The species is also reported to occur in a couple of crater lakes just to the north of Lake Malawi, in Tanzania.
Crater Lake Populations
Some specimens reportedly collected from Lake Tschungruru in Tanzania were identified as O. lidole by Trewavas. This lake appears to be the Kiungululu Crater (9°18′24.06″S 33°51′54.31″E), which is situated at an altitude of around 450m above the present surface of Lake Malawi. How they got there is a mystery. Some of these fish were sexually mature at sizes of 14-17cm, which is much smaller than mature fish in Lake Malawi. Subsequently, smallish mature specimens were also collected from Lake Kingiri, which is only about 50m higher up than the main lake (9°25′07.67"S 33°51′29.29″E).
Exploitation and Conservation Status
Oreochromis lidole was formerly an important food fish on Lake Malawi. It was particularly abundant in the catches of trawlers operating in the South Eastern Arm from Maldeco. Populations of all chambo species declined drastically in the 1990s, but O.lidole appears to have been hardest hit, and on recent surveys was extremely uncommon. The IUCN red listing as 'Endangered' seems justified and indeed may be overoptimistic. The status of the Tanzanian Crater lake populations is unknown.