Oreochromis lidole

Oreochromis lidole is a species of freshwater fish in the family Cichlidae. This tilapia is endemic to Malawi, Mozambique and Tanzania, where restricted to Lake Malawi, Lake Malombe and the Shire River. It was important in fisheries, but has drastically declined; it may already be extinct.[1] This oreochromine cichlid is locally called Chambo,[1] a name also used for a few other closely related species found in the same general region.[2]

Oreochromis lidole
Emaciated ('spent') female from Malembo, Lake Malawi
Juvenile from Cape Maclear, Lake Malawi

Critically endangered, possibly extinct  (IUCN 3.1)[1]
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Cichliformes
Family: Cichlidae
Genus: Oreochromis
Species:
O. lidole
Binomial name
Oreochromis lidole
(Trewavas, 1941)
Synonyms
  • Tilapia lidole Trewavas, 1941
  • Sarotherodon lidole (Trewavas, 1941)

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.[3] 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.[4]

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.[4]

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.[5] Females often migrate to more productive turbid waters to release their young, in areas such as Lake Malombe.[6]

Diet

Oreochromis lidole feeds mainly on plankton- including crustaceans, such as Bosmina and Diaptomus, diatoms such as Aulacoseira and Surirella and other larger algae.[7]

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.[4]

Crater lake populations

Some specimens reportedly collected from Lake Tschungruru in Tanzania were identified as O. lidole by Trewavas.[4] 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. 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). These identifications have not been confirmed by recent surveys of these lakes.[8]

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,[9] but O. lidole appears to have been hardest hit, and on recent surveys was extremely uncommon. The IUCN red listing as 'Critically Endangered (Possibly Extinct)' seems justified.

References
  1. Konings, A. (2018). "Oreochromis lidole". IUCN Red List of Threatened Species. 2018: e.T61276A47243265. doi:10.2305/IUCN.UK.2018-2.RLTS.T61276A47243265.en.
  2. Turner, G.F.; N.C. Mwanyama (1992). "Distribution and Biology of Chambo (Oreochromis spp.) in Lakes Malawi and Malombe". Food and Agriculture Organization, United Nations. Retrieved 6 November 2019.
  3. Trewavas, Ethelwynn (1941). "Nyasa fishes of the genus Tilapia and a new species from Portuguese East Africa". Annals and Magazine of Natural History. 7 (39): 294–306. doi:10.1080/00222934108527158. ISSN 0374-5481.
  4. Trewavas, Ethelwynn (1983). Tilapiine fishes of the genera Sarotherodon, Oreochromis, and Danakilia /. London: British Museum (Natural History). doi:10.5962/bhl.title.123198.
  5. 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, Oveochvomis (Nyasalapia) spp". Journal of Fish Biology. 39 (6): 775–782. doi:10.1111/j.1095-8649.1991.tb04407.x. ISSN 0022-1112.
  6. 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)
  7. 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". Journal of Fish Biology. 39 (1): 15–24. doi:10.1111/j.1095-8649.1991.tb04337.x. ISSN 0022-1112.
  8. Shechonge, Asilatu; et al. (2018). "Widespread colonisation of Tanzanian catchments by introduced Oreochromis tilapia fishes: the legacy from decades of deliberate introduction". Hydrobiologia. 832 (1): 235–253. doi:10.1007/s10750-018-3597-9. PMC 6394791. PMID 30880833.
  9. Turner, George F. (1995), "Management, conservation and species changes of exploited fish stocks in Lake Malaŵi", The Impact of Species Changes in African Lakes, Springer Netherlands, pp. 365–395, doi:10.1007/978-94-011-0563-7_17, ISBN 9789401042499
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