Editing Hippopotamus (section)

===In zoos===
[[File:Obaysch 1852.jpg|thumb|right|[[Obaysch]] lounging at the [[London Zoo]] in 1852]]
Hippos have long been popular zoo animals. The first record of hippos taken into captivity for display is dated to 3500 BC in Hierakonpolis, Egypt.<ref>{{cite journal |author=Rose, M. |year=2010|title=World's first Zoo-Hierakonpolis, Egypt. |journal=Archaeology |volume=63 |issue=1 |pages=25–32}}</ref> The first zoo hippo in modern history was [[Obaysch]], who arrived at the [[London Zoo]] on 25 May 1850, where he attracted up to 10,000 visitors a day and inspired a popular song, the "Hippopotamus Polka".<ref name=Mania>{{Cite journal |author=Root, N. J. |title=Victorian England's Hippomania |journal=[[Natural History (magazine)|Natural History]] |volume=103 |year=1993 |pages=34–39}}</ref>

Hippos generally breed well in captivity; birth rates are lower than in the wild, but this can be attributed to zoos' desire to limit births, since hippos are relatively expensive to maintain.<ref name=Mania/><ref>{{cite journal|last1=Snyder|first1=K. D. |title=The common Hippopotamus in the wild and in captivity: Conservation for less charismatic species |journal=Journal of International Wildlife Law & Policy |date=2015 |volume=18 |issue=4 |pages=337–354 |doi=10.1080/13880292.2015.1096162 |s2cid=86295612}}</ref> Starting in 2015, the [[Cincinnati Zoo]] built a US$73 million exhibit to house three adult hippos, featuring a {{cvt|250,000|L}} tank. Modern hippo enclosures also have a complex filtration system for the animal's waste, an underwater viewing area for the visitors, and glass that may be up to {{cvt|9|cm}} thick and capable of holding water under pressures of {{cvt|31|kPa}}.<ref name=reaktion/>{{rp|158–159}}