Oreochromis lidole

Oreochromis lidole
File:Lidole female Feb07 Malembo1.jpg
Emaciated ('spent') female from Malembo, Lake Malawi
File:Lidole.JPG
Juvenile from Cape Maclear, Lake Malawi
Conservation status
Endangered (IUCN 3.1)
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	Perciformes
Family:	Cichlidae
Genus:	Oreochromis
Species:	O. lidole
Binomial name
Oreochromis lidole (Trewavas, 1941)
Synonyms
Tilapia lidole Trewavas, 1941 Sarotherodon lidole (Trewavas, 1941)

Oreochromis lidole is a species of fish in the Cichlidae family. It is endemic to Malawi and can be found in Lake Malawi, Lake Malombe and in the Shire River in Malawi. Its natural habitats are rivers and freshwater lakes. It is more popularly referred to as 'Chambo'.

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.

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.

It is more commonly referred to as Chambo.

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 17–20 cm 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: 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 5 cm 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 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 50 m. 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 450 m above the present surface of Lake Malawi. How they got there is a mystery. Some of these fish were sexually mature at sizes of 14–17 cm, 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.

References

• Lowe, R.H. (1953) Notes on the ecology and evolution of Nyasa fishes of the genus Tilapia, with a description of T.saka Lowe. Proc. zool. Soc. Lond. 122:1041–1053.
• Robinson, R.L., Turner, G.F., Pitcher, T.J. & Grimm, A.S. (1995). An experimental study of phytoplankton feeding in three tilapiine species. J. Fish Biology 46, 449-456.
• Seisay, M.B.D., van Zalinge, N.P. & Turner, G.F. (1992a) Relationships between chambo stocks of Lake Malombe, the Upper Shire River and Lake Malawi. GOM/FAO/UNDP MLW/86/013 Field Document 18, July 1992.
• Seisay, M.B.D., van Zalinge, N.P. & Turner, G.F. (1992b) Population dynamics and stock estimates of chambo (Oreochromis spp.) in the South-East Arm and Lake Malombe- length-based approach. GOM/FAO/UNDP MLW/86/013 Field Document 19.
• Sodsuk, P. MacAndrew, B.A. & Turner, G.F. (1995). Allozyme variation in Oreochromis species from Lake Malawi: implications for evolutionary relationships. J. Fish Biology 47, 321-333.
• Trewavas, E. (1942) Nyasa fishes of the genus Tilapia and a new species from Portuguese East Africa. Ann. Mag. Nat. Hist. 11:294–306.
• Trewavas, E. (1983) Tilapiine fishes of the genera Sarotherodon, Oreochromis and Danakilia. London: British Museum (Natural History). 583pp.
• Turner, G.F. (1995) Management, conservation and species changes of exploited fish stocks in Lake Malawi, In: T.J. Pitcher & P.J.B. Hart, eds. The Impact of Species Changes in African Lakes. London, Chapman & Hall, pp. 365–395.
• Turner, G.F. Oreochromis lidole http://www.malawicichlids.com/mw10001b.htm
• Turner, G.F. & Mwanyama, N.C. (1992) Distribution and biology of Chambo (Oreochromis spp.) in Lake Malawi and Malombe. GOM/UNDP/FAO Chambo Fisheries Research Project, Malawi. FI:DP/MLW/86/013, Field Document 21: 26p. (http://www.fao.org/docrep/006/ad202e/AD202E00.htm#TOC)
• Turner, G.F. & Robinson, R.L. (1990) Ecology, morphology and taxonomy of the Lake Malawi Oreochromis (Nyasalapia) species flock. Ann. Mus. Roy. Afr. Centr. Sc. Zool. 262, 23–28.
• Turner, G.F., Grimm, A.S., Mhone, O.K., Robinson, R.L. & Pitcher, T.J. (1991) The diet of Oreochromis lidole (Trewavas) and other chambo species in Lakes Malawi and Malombe. J. Fish Biol. 39, 15–24.
• Turner, G.F., Witimani, J., Robinson, R.L., Grimm, A.S. & Pitcher, T.J. (1991) Reproductive isolation and the nest sites of Lake Malawi chambo, Oreochromis (Nyasalapia) spp. J.Fish Biol. 39, 775–782.