{{Short description|Species of fish}} {{Use dmy dates|date=December 2022}} {{Speciesbox | image = Oreochromis_hunteri_1.jpg | status = CR | status_system = IUCN3.1 | status_ref = <ref name="iucn status 16 November 2021">{{cite iucn |author=Bayona, J.D.R. |author2=Odhiambo, E.A. |author3=Hanssens, M. |date=2006 |title=''Oreochromis hunteri'' |volume=2006 |article-number=e.T60634A12389528 |doi=10.2305/IUCN.UK.2006.RLTS.T60634A12389528.en}}</ref> | taxon = Oreochromis hunteri | authority = Günther, 1889 | synonyms = * ''Sarotherodon hunteri'' <small>(Günther, 1889)</small> * ''Tilapia hunteri'' <small>(Günther, 1889)</small> }}
The '''Lake Chala tilapia''' ('''''Oreochromis hunteri''''') is a species of cichlid fish that is endemic to Lake Chala, a small crater lake on the border of Kenya and Rombo District of Kilimanjaro Region in Tanzania.<ref name="iucn status 16 November 2021" /><ref name=FishBase>{{FishBase |genus= Oreochromis|species= hunteri| month = September | year = 2019}}</ref> It mostly lives in relatively deep water, at depths between {{cvt|20-45|m|ft}}.<ref name=Moser2019>{{cite journal| author1=Moser, F.N. | author2=J.C. van Rijssel | author3=B. Ngatunga | author4=S. Mwaiko | author5=O. Seehausen | year=2019 | title=The origin and future of an endangered crater lake endemic; phylogeography and ecology of ''Oreochromis hunteri'' and its invasive relatives | journal=Hydrobiologia | volume=832 | issue=1 | pages=283–296 | doi=10.1007/s10750-018-3780-z| s2cid=52944759 | url=https://boris.unibe.ch/120465/ }}</ref> It is considered critically endangered by the IUCN, with the two primary threats being deterioration of its habitat due to siltation,<ref name="iucn status 16 November 2021" /> and other non-native tilapia species that have been introduced to Lake Chala.<ref name=FishBase/><ref name=Moser2019/> Before these introductions, the Lake Chala tilapia was the only fish in Lake Chala.<ref name=Dieleman2019>{{cite journal| author1=Dieleman, J. | author2=M. Muschick | author3=W.D. Nyingi | author4=D. Verschuren | year=2019 | title=Species integrity and origin of ''Oreochromis hunteri'' (Pisces: Cichlidae), endemic to crater Lake Chala (Kenya–Tanzania) | journal=Hydrobiologia | volume=832 | issue=1 | pages=269–282 | doi=10.1007/s10750-018-3570-7 | s2cid=4591524 | url=https://boris.unibe.ch/116496/ }}</ref> It is very closely related to the similar Jipe tilapia (''O. jipe''), another highly threatened species from the same general region of Kenya and Tanzania.<ref name=Moser2019/><ref name=Dieleman2019/> The Lake Chala tilapia can reach a standard length of up to {{cvt|30|cm|in}}.<ref name=FishBase/>
The specific name ''hunteri'' honours the British zoologist Henry C. V. Hunter (1861-1934), who collected the type, and who provided notes on this species' distribution.<ref name = ETYFish>{{cite web | url = http://www.etyfish.org/cichlidae4/ | title = Order CICHLIFORMES: Family CICHLIDAE: Subfamily PSEUDOCRENILABRINAE (l-o) | access-date = 4 February 2019 | author1 = Christopher Scharpf | author2 = Kenneth J. Lazara | name-list-style = amp | work = The ETYFish Project Fish Name Etymology Database | publisher = Christopher Scharpf and Kenneth J. Lazara | date = 4 December 2018}}</ref> ''O. hunteri'' is the type species of the genus ''Oreochromis''.<ref name=Moser2019/>
== Taxonomy == This species belongs to the family Cichlidae and the genus ''Oreochromis.'' Cichlid species in the genus ''Oreochromis'' are widely used in aquaculture around the world and provide an important source of food and income for many East African people<ref name="Moser2019" />. Many species in the genus ''Oreochromis'' have potential to hybridize with another, meaning they can cross breed and reproduce due to their genetic compatibility<ref name=":0">{{Cite book |last=Genner |first=Martin |title=A GUIDE TO THE TILAPIA FISHES OF TANZANIA |date=August 2018 |publisher=Martin Genner }}</ref>. ''O. hunteri'' is an endemic species to Lake Chala meaning it is only found there and nowhere else in the world. The endemic species in the Pagnani system region which includes Lake Chala are ''O. jipe'' and ''O. pangani'' who are all closely related to ''O. hunteri'' <ref name="Moser2019" /><ref name="Dieleman2019" />''.'' alt=A phylogeographic Tree of Lake Chala Tilapia species, showing how distant closley related they across the Pagani Drainage Basin |thumb|448x448px|Phylogeographic Tree of Tilapia in Lake Chala from Moser ''et al.'' 2019. This tree demonstrates how unique ''O. hunteri'' is from modern Tilapia representing a unique evolutionary lineage Given the genetic compatibility between species of the genus ''Oreochromis,'' studies show that they are morphologically distinct from one another, with having longer and wider heads, shorter lower jaws and smaller or bigger eyes<ref name="Moser2019" />. As new Cichlid species begin to colonize, the phylogenetic tree within this genus starts to show an early sign of divergence as many studies conducted within the Pagnani system show evidence of ecological diversification among the cichlids in Lake Chala<ref>{{Cite journal |last=Bradbeer |first=Stephanie J. |last2=Harrington |first2=Jack |last3=Watson |first3=Henry |last4=Warraich |first4=Abrahim |last5=Shechonge |first5=Asilatu |last6=Smith |first6=Alan |last7=Tamatamah |first7=Rashid |last8=Ngatunga |first8=Benjamin P. |last9=Turner |first9=George F. |last10=Genner |first10=Martin J. |date=2019-04-01 |title=Limited hybridization between introduced and Critically Endangered indigenous tilapia fishes in northern Tanzania |url=https://doi.org/10.1007/s10750-018-3572-5 |journal=Hydrobiologia |language=en |volume=832 |issue=1 |pages=257–268 |doi=10.1007/s10750-018-3572-5 |issn=1573-5117 |pmc=6394572 |pmid=30880834}}</ref>.
== Description == ''O. hunteri'' is characterized by their large, compressed bodies with a terminal mouth and forward snout. Teeth are small oriented in a narrow band made to crush shells of small invertebrates and a narrow pharyngeal bone. Their dorsal fins are continuous with 15-18 spines and 12-14 rays. Anal fins have 3 spines and 7 –12 rays. They also have a truncate caudal fin, which provide a balance of speed and mobility<ref>{{Cite book |last=Eccles |first=D.H |title=FAO species identification sheets for fishery purposes. Field guide to the freshwater fishes of Tanzania |publisher=FAO |year=1992 |isbn=925103186X}}</ref>.
Little is known about the early life stages and morphological developments of ''O. hunteri,'' however, tilapia juvenile morphology differ from adults. Being closely related from the phylogeographic tree, ''O. jipe'' and ''O''. ''pangani'' share a similar evolutionary background within the Lake Chala river. Studies show that this genus have a moderate growth rate and are sexually matured when they reach at least 8 – 10 cm in length. Juveniles of these species have a slender body with vertical bars and mottled pigmentation for possible camouflage to avoid predation<ref name=":1">{{Cite book |last=Trewavas |first=Ethelwynn |title=Tilapiine Fishes of the Genera Sarotherodon, Oreochromis, and Danakilia |publisher=British Museum (Natural History) |year=1983 |isbn=9780565008789}}</ref>. Bar marks start to fade as juveniles grow, and bodies start becoming more vertically compressed and the sexual dimorphic characteristics start to become noticeable between male and females.
Males are characterized with a melanin pattern on top of their head, their flank scales are darker on the posterior side of the fish, and a light grey-blue background. The dorsal fins are much darker in color than their ventral side. Females have fewer contrasting colors with flanks being grey in color or olive with a lighter ventral side region<ref name=":0" />.
== Distribution == thumb|458x458px|Map of the Pangani River drainage system from Moser ''et al.'' 2019 ''O. hunteri'' is native to Lake Chala, a small (4.2 km²) crater lake located on the border between Kenya and Tanzania near Mount Kilimanjaro (3°19′S, 37°42′E)<ref name="Moser2019" />. ''O. hunteri'' consists of occupying zones in the water column that is near the shore, which is known as the littoral zone, as well as open pelagic waters of the lake which is known as the limnetic zone. However, from the introduction of invasive tilapia species, ''O. hunteri'' has a much narrower distribution, demonstrating a higher abundance in the limnetic zone of Lake Chala. Catches have been recorded from depths between 20 and 45 meters showing how competition from invasive tilapia species changed their distribution abundance in Lake Chala resulting in major feeding partitioning<ref name="Moser2019" />.
== Biology == The biology of ''O. hunteri'' follows many typical tilapia character traits but also reflects unique feeding methods specialized to an isolated crater lake environment. Females are maternal mouthbrooders in which they carry their offspring in their mouths to ensure the best survivability for their offspring<ref name=":0" />. They have showcase multiple spawning events per year. Although little data is known to fecundity, age of maturity and maximum lifespan for Lake Chala tilapia, however inferred patterns from closely related species like ''O. jipe'' and ''O. pangani'' indicate females are typically paler and lighter in mouthbrooding periods following the consistent trend of spawning seasonally throughout the year which are traits likely to be similar to ''O. hunteri''<ref name=":1" />''.'' alt=Depth on the y -axis. Proportion of Abundance on x-axis|thumb|432x432px|Abundances of Tilapia in Lake Chala from Moser ''et al.'' 2019 ''O. hunteri'' are an important ecological contributor among native fish fauna as a primary consumer and reflect their specialization in nutrient limited waters. Due to the diverse niche, Lake Chala provides many numerous cichlid populations which are omnivorous due to the adaptation to lacustrine habitats where the water is not flowing and surrounded by vegetation, as well as dietary<ref name="Moser2019" />.
Their feeding method primarily involves coursing in the water column eating algae and phytoplankton in the limnetic zone. While not the fast swimmers, they swim moderately long distances with their truncate caudal fins and using their narrow small bands of teeth to feed on phytoplankton and algae<ref name="Dieleman2019" />. Many gastropods in the genus ''Melanoide'' were documented in high abundance, which prompted the Lake Chala cichlids to occasionally consume small invertebrates as it eats detritus along the soft bottom<ref name="Dieleman2019" />. Due to the small isolated habitat, ''O. hunteri'' maintained a narrow niche focused on benthic detrital resources, which is organic material on the lake bottom, because of the introduction of invasive species of Tilapia in Lake Chala that reinforced ''O. hunteri'' specialization on detrital and algal material<ref name="Moser2019" />.
== Conservation status == ''Oreochromis hunteri'' is currently listed as critically endangered, due to its limited geographic range from being in a single crater and having its realized niche smaller due to competition from the invasive tilapia species. ''O. hunteri'' is a specialist in its native habitat evolving in a closed ecosystem with no other competing species for many years in the past. The isolation of ''O. hunteri'' narrowed its niche specializing on feeding benthic detritus and algae. Following the introduction of invasive tilapia species into Lake Chala, recent studies indicate ''O. hunteri'' underwent adaptive loss in its habitat due to losing its territoriality shifting to a sympatric environment, meaning they are living alongside other species. Phenotypic variability within Lake Chala Tilapia remained consistent and there was no hybridization with other invasive species, giving us an understanding that ''O. hunteri'' did not acquire new traits or character displacement from the invasive tilapia species which caused its niche breadth to be smaller due to exploitative competition, resulting in competitive exclusion, forcing ''O. hunteri'' to feed in deeper waters which marked them as critically endangered from the IUCN<ref>{{Cite web |last=Kosgei |first=G |date=2006 |title=Lake Chala Tilapia |url=https://www.iucnredlist.org/species/60634/12389528 |access-date= |website=IUCN Red List}}</ref>.
Another reason for their decline in population is habitat destruction. Lake Chala’s habitat, being next to a mountain, has run off, increasing turbidity and the amount of sunlight in Lake Chala <ref>{{Cite journal |last=Zhang |first=Xiufeng |last2=Mei |first2=Xueying |last3=Gulati |first3=Ramesh D. |date=2017-03-01 |title=Effects of omnivorous tilapia on water turbidity and primary production dynamics in shallow lakes: implications for ecosystem management |url=https://www.researchgate.net/publication/310515746 |journal=Reviews in Fish Biology and Fisheries |language=en |volume=27 |issue=1 |pages=245–254 |doi=10.1007/s11160-016-9458-6 |issn=1573-5184 }}</ref>. In addition, anthropogenic factors cause inter-annual climate variability limiting the amount of deep-water nutrients to be upwelled, resulting in a decline of algae and phytoplankton being available for ''O. hunteri''<ref name="Moser2019" />. Lake Chala Tilapia populations have survived major climate-driven alterations in the past, however, with the pressures of competition and having to cope with climate change may eventually lead to a linear decline of ''O. hunteri''.
Proper management and monitoring of the current population size trends and patterns are necessary to find solutions and reduce the numbers of newly introduced species so that ''O. hunteri'' aren’t outcompeted in the wild. A good demographic modeling to further study life history parameters can be a good remedy to better understand fecundity and lifespan
==References== {{Reflist}}
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Lake Chala tilapia Category:Freshwater fish of Kenya Category:Freshwater fish of Tanzania Category:Critically endangered fauna of Africa Category:Fish described in 1889 Category:Taxa named by Albert Günther Category:Taxonomy articles created by Polbot