Oreochromis lidole

Oreochromis lidole
Emaciated ('spent') female from Malembo, Lake Malawi
Juvenile fromCape Maclear,Lake Malawi
Conservation status
Critically endangered,possibly extinct(IUCN 3.1)
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	Cichliformes
Family:	Cichlidae
Genus:	Oreochromis
Species:	O. lidole
Binomial name
Oreochromis lidole (Trewavas,1941)
Synonyms
Tilapia lidoleTrewavas, 1941 Sarotherodon lidole(Trewavas, 1941)

Oreochromis lidoleis a species offreshwater fishin the familyCichlidae.Thistilapiais native toMalawi,MozambiqueandTanzania,where it is found inLake Malawi,Lake Malombe,theShire Riverand perhaps some crater lakes further north. It is important in fisheries, but has drastically declined; it may already beextinct.Thisoreochromine cichlidis locally calledchambo,a name also used for two other closely related species found in the same region,O. karongaeandO. squamipinnis.

Names

The species was described asTilapia lidolein 1941 by the BritishichthyologistEthelwynn Trewavas,from specimens she had collected on a fishery survey ofLake Malawiin 1939.She reported that the name was derived from the local name 'dole', although it was also known asgalamulaorlolo,or more generally aschamboalong with similartilapiaspecies. Along with othermouthbroodingtilapia species, it was reclassified in the genusSarotherodonin 1976, and later moved into the genusOreochromis,along with other species showing clearsexual dimorphism(differences in size, shape and colour between the sexes). It has also been included in the subgenusNyasalapiaalong with other species where the males develop long, branching genital papillae.

Distinguishing features

Juvenilesof the variouschambospecies 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 thedorsal fin.Oreochromis lidolecan be distinguished from the other closely related 'chambo' species at lengths of about 17–20 cm (6.7–7.9 in) or greater, as it generally assumes a big-headed, skinny appearance, resulting from its shallower body, larger mouth and biggeropercularplates (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 ofO. karongae,but enables them to be distinguished from those ofO. squamipinnis.

Reproductive biology

Like all other knownOreochromis,O. lidoleis a maternalmouthbrooder:females carry the eggs and small juveniles in their mouths for several weeks. When juveniles have absorbed theiryolksacs, 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 (2.0 in) long. Breeding mainly occurs during the hot season from October to January, when males gather in deep water (mainly 20–45 m (66–148 ft)) off clean, steeply shelving beaches to dig huge craters (1–3 m (3 ft 3 in – 9 ft 10 in) in diameter) in which courtship and spawning takes place.Females often migrate to more productive turbid waters to release their young, in areas such asLake Malombe.

Diet

Oreochromis lidolefeeds mainly onplankton- includingcrustaceans,such asBosminaandDiaptomus,diatomssuch asAulacoseiraandSurirellaand other largeralgae.

Distribution

Oreochromis lidolehas been recorded from throughoutLake Malawi,where it tends to live in deeper, less muddy habitats than relatedchambospecies, although they are often found together in the same fisherman's catch, suggesting they may shoal together. Like otherchambo,they are rarely caught deeper than around 50 m. Juveniles and brooding females tend to be found in shallower, muddier water, in places such asLake Malombe.The species was reportedly most common in the productive southern arms of the lake, and rare off muddy or rocky coasts.

Crater lake populations

Some specimens reportedly collected fromLake Tschungruruin Tanzania were identified asO. lidoleby Trewavas.This lake appears to be theKiungululu Crater(9°18′24.06″S 33°51′54.31″E), which is situated at an altitude of around 450 m (1,480 ft) above the present surface of Lake Malawi. Some of these fish were sexually mature at sizes of 14–17 cm (5.5–6.7 in), which is much smaller than mature fish in Lake Malawi. Subsequently, smallish mature specimens were also collected fromLake Kingiri,which is only about 50 m (160 ft) 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.

Exploitation and conservation status

Oreochromis lidolewas formerly an importantfood fishon Lake Malawi. It was particularly abundant in the catches of trawlers operating in the South Eastern Arm fromMaldeco.A study by Turner found populations of allchambospecies declined drastically in the 1990s.Catches ofchamboin one part of the southern arm of Lake Malawi dropped from 70 kg (150 lb) a boat a day to 4.5 kg (9.9 lb) in the period between 2006 and 2016. Despite hundreds ofchambobeing caught every day, because no one has identified thesechamboas specificallyO. lidoleas of 2016, theIUCNstated that no one knows for sure if anyone has seenO. lidolesince Turner last identified a fish as such in 1992, and thus declared that it may be extinct for all anyone knows.