Oreochromis Amphimelas

''Oreochromis amphimelas'' is a species of tilapia cichlid endemic to north–central Tanzania, where it is found in Lake Manyara and a number of other saline lakes with closed basins. Maximum recorded size is in standard length.

Description

This is an unusual-looking tilapia: the front part of the head is very short, so it has a small eye, small mouth and short snout. The smaller fish have a rather cylindrical body, but the largest fish have a high, arched back and a concave head profile. The mouth is quite upwardly-angled. The gill arches hold relatively few gill rakers: only 12–16 on the lower part of the outermost arch, the arches lack microbranchiospines and the number of dorsal fin spines is only 12–14, which is rather low compared to other ''Oreochromis''. Females and immatures are a silvery grey, but show little sign of vertical bars on the flanks or a 'tilapia mark' at the base of the soft dorsal fin shown by most other tilapias. Mature males are dark pinkish with black heads, bellies, and conspicuously black dorsal, anal and pelvic fins.

Taxonomy and systematics

The species was described as ''Tilapia amphimelas'' by Franz Martin Hilgendorf at the Natural History Museum, Berlin in 1905 from male specimens collected from Lake Manyara by Oscar Neumann between 1893 and 1895. The name, meaning 'double-black', probably refers to the dark upper and lower fins of the breeding male. In the same paper, females of the same species were described as ''Tilapia manyarae'', a possibility considered by Hilgendorf. In the 1960s, it was suggested that this species was closely related to the highly specialised soda lake cichlids from Lakes Magadi and Natron, now regarded as members of the genus ''Alcolapia''. In the 1980s, Ethelwynn Trewavas separated them into separate subgenera, creating the little-used subgenus ''Vallicola'' for ''O. amphimelas''. Genetic evidence published in 2019 supported earlier theories, indicating that ''O. amphimelas'' (along with '' O. esculentus'') is closer to ''Alcolapia'' than it is to other ''Oreochromis''.

Reproduction

The species is a maternal mouthbrooder, like all other known species of the genus ''Oreochromis''. Eggs are about 2–2.5mm in diameter. In Lake Manyara maturity is reached at around 7–8 cm SL. Females appear to grow larger than males, which is unusual in ''Oreochromis'' and cichlids in general.

Distribution

The type locality is Lake Manyara in northern Tanzania. This shallow lake is a closed basin, with inflowing streams but no outflow. The water level varies between seasons and years, leading to marked fluctuation in salinity and alkalinity. It has also been recorded from Lakes Eyasi, Kitangiri and Singida. These are also closed basins, but Kitangiri and Singida are generally less saline. ''Oreochromis amphimelas'' appears to attain much larger sizes (to 33 cm in total length) in these lakes, compared to the saltier Manyara and Eyasi (max 13 cm in total length). Recently, ''O. amphimela''s has been reported from another closed saline lake, Lake Sulunga (or Sulungali), near Dodoma.

Exploitation and conservation

The species is heavily fished where it is found. It is threatened by stocking of exotic tilapia species, including ''Oreochromis esculentus, Oreochromis niloticus, Oreochromis leucostictus'' and '' Coptodon spp.'', all which have been reported from catchments inhabited by ''O. amphimelas''. Some of these species are believed to have hybridised with ''O. amphimelas''.

References

{{Taxonbar, from=Q1827051

amphimelas
Endemic fauna of Tanzania
Fish of Tanzania
Cichlid fish of Africa
Lake Manyara
Endangered animals
Endangered biota of Africa
Taxonomy articles created by Polbot
Taxa named by Franz Martin Hilgendorf
Fish described in 1905