Editing Lake Victoria (section)

===Invasive fish===
Starting in the 1950s, many species have been [[Introduced species|introduced]] to Lake Victoria where they have become [[Invasive species|invasive]] and a prime reason for the extinction of many [[endemic]] [[haplochromine]] cichlids.<ref name="Witte1992"/> Among the introductions are several [[tilapia]]s: [[Redbreast tilapia|redbreast]] (''Coptodon rendalli''), [[Redbelly tilapia|redbelly]] (''C. zillii''),  Nile (''Oreochromis niloticus'') and [[Oreochromis leucostictus|blue-spotted tilapias]] (''O. leucostictus'').<ref name="Lowe2009"/><ref name="Njiru2005"/><ref name="Pringle2005">Pringle, R.M. (2005). [https://academic.oup.com/bioscience/article/55/9/780/286121/The-Origins-of-the-Nile-Perch-in-Lake-Victoria The Origins of the Nile Perch in Lake Victoria.] BioScience 55 (9): 780–787.</ref> Although these have contributed to the extinction of native fish by causing significant changes to the [[ecosystem]], outcompeted natives and (in the case of the Nile tilapia) possibly hybridized with the highly threatened native tilapias, the most infamous introduction was the large and highly predatory [[Nile perch]] (''Lates niloticus'').<ref name="Witte1992"/><ref name="Lowe2009"/><ref name="Njiru2005"/>

[[File:Lates niloticus 2.jpg|thumb|upright|The [[Nile perch]] was introduced to Lake Victoria for fishing, and can reach up to {{convert|2|m|ft|abbr=on}} and {{convert|200|kg|lb|abbr=on}}.<ref>{{FishBase | genus = Lates | species = niloticus  | month = March| year = 2017}}</ref>]]
As early as the 1920s, it was proposed to introduce a large pelagic predator such as the Nile perch to improve the fisheries in the lake. At the same time it was warned that this could present a serious danger to the native fish species and required extensive research into possible ecological effects before done.<ref name="Pringle2005"/> These warnings primarily concerned the native tilapia ''O. esculentus'', as the smaller haplochromine cichlids (despite playing an important role in local fisheries) were regarded as "trash fish" by the colonial government.<ref name="Pringle2005"/> In the following decades, the pressure to introduce the Nile perch continued, as did warnings about the possible effects of doing it.<ref name="Pringle2005"/> The first introduction of Nile perch to the region, done by the [[Uganda Game and Fisheries Department]] (then part of the colonial government) and local African fish guards, happened upstream of Murchison Falls directly after the completion of the Owen Falls Dam in 1954. This allowed it to spread to Lake Kyoga where additional Nile perch were released in 1955, but not Victoria itself.<ref name="Pringle2005"/> Scientists argued that further introduction should wait until research showed the effect of the introduction in Kyoga, but by the late 1950s, Nile perch began being caught in Lake Victoria.<ref name="Pringle2005"/> As the species was already present, there were few objections when more Nile perch were transferred to Victoria to further bolster the stock in 1962–63.<ref name="Pringle2005"/> 

The origin of the first Victoria introductions in the 1950s is not entirely clear and indisputable evidence is lacking. Uganda Game and Fisheries Department (UGFD) officials denied that they were involved, but circumstantial evidence suggests otherwise and local Africans employed by UGFD have said that they introduced the species in 1954–55 under the directive of senior officials.<ref name="Pringle2005"/> UGFD officials argued that Nile perch must have spread to Lake Victoria by themselves by passing through the Owen Falls Dam when shut down for maintenance, but this is considered highly unlikely by many scientists.<ref name="Pringle2005"/> The Nile perch had spread throughout the lake by 1970.<ref name="Lowe2009"/> Initially the population of the Nile perch was relatively low, but a drastic increase happened, peaking in the 1980s, followed by a decline starting in the 1990s.<ref name="Lowe2009"/>

Due to the presence of the Nile perch, the natural balance of the lake's ecosystem has been disrupted. The food chain is being altered and in some cases, broken by the indiscriminate eating habits of the Nile perch.
The subsequent decrease in the number of algae-eating fish allows the algae to grow at an alarming rate, thereby choking the lake. The increasing amounts of algae, in turn, increase the amount of detritus (dead plant material) that falls to the deeper portions of the lake before decomposing. As a by-product of this the oxygen levels in the deeper layer of water are being depleted. Without oxygen, any aerobic life (such as fish) cannot exist in the deeper parts of the lake, forcing all life to exist within a narrow range of depth. In this way, the Nile perch has degraded the diverse and thriving ecosystem that was once Lake Victoria. The abundance of aquatic life is not the only dependent of the lake: more than thirty million people in Tanzania, Kenya and Uganda rely on the lake for its natural resources.

Hundreds of endemic species that evolved under the special conditions offered by the protection of Lake Victoria have been lost due to extinction, and several more are still threatened.<ref>{{cite journal |last1=Breitinger |first1=Jan C. |date=24 November 2021 |title=A Lake to Serve: The Exploration, Modification, and Degradation of Lake Victoria, 1920s to 1960s |url=https://www.tandfonline.com/doi/full/10.1080/03086534.2021.1985212 |journal=The Journal of Imperial and Commonwealth History |volume=50 |issue=1 |pages=144–184 |doi=10.1080/03086534.2021.1985212 |s2cid=244667637 |access-date=22 July 2022}}</ref> Their loss is devastating for the lake, the fields of ecology, genetics and evolution biology, and more evidently, for the local fisheries. Local fisheries once depended on catching the lungfish, tilapia, carp and catfish that comprise the local diet.
Today, the composition and yields of such fish catches are virtually negligible. Extensive fish kills, Nile perch, loss of habitat and overfishing have caused many fisheries to collapse and many protein sources to be unavailable at the market for local consumption. Few fisheries, though, have been able to make the switch to catching the Nile perch, since that requires a significant amount of capital resources.<ref>{{cite web|url=http://www.homehighlight.org/entertainment-and-recreation/nature/nile-perch-and-the-future-of-lake-victoria.html |title=Nile Perch and the Future of Lake Victoria |access-date=2015-01-11 |url-status=dead |archive-url=https://web.archive.org/web/20150111223808/http://www.homehighlight.org/entertainment-and-recreation/nature/nile-perch-and-the-future-of-lake-victoria.html |archive-date=2015-01-11 }}</ref>