Editing Swarm behaviour (section)

====Fish====
{{Main|Shoaling and schooling}}
[[File:Moofushi Kandu fish.jpg|thumb|[[Shoaling and schooling|Schooling]] predator fish size up schooling [[anchovy|anchovies]]]]
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|image1=[https://www.youtube.com/watch?v=kI1aU1RVILY Foraging efficiency]<ref>Pitcher et al. 1982.</ref>
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The term "shoal" can be used to describe any group of fish, including mixed-species groups, while "school" is used for more closely knit groups of the same species swimming in a highly synchronised and polarised manner.

Fish derive many benefits from shoaling behaviour including defence against predators (through better predator detection and by diluting the chance of capture), enhanced [[foraging]] success, and higher success in finding a mate.<ref name="Pitcher 1993">Pitcher TJ and Parish JK (1993) [https://books.google.com/books?id=10lElCT7v5wC&dq=%22Behaviour+of+teleost+fishes%22+%22%22Functions+of+shoaling+behaviour+in+teleosts%22%22&pg=PA363 "Functions of shoaling behaviour in teleosts"] In: Pitcher TJ (ed) ''Behaviour of teleost fishes''. Chapman and Hall, New York, pp 363–440</ref> It is also likely that fish benefit from shoal membership through increased [[hydrodynamic]] efficiency.<ref name="Hoare et al. 2000">Hoare DJ, Krause J, Peuhkuri N and Godin JGJ (2000) [https://archive.today/20130105143046/http://www3.interscience.wiley.com/journal/119004845/abstract?CRETRY=1&SRETRY=0 ''Body size and shoaling in fish''] Journal of Fish Biology, 57(6) 1351-1366.</ref>

Fish use many traits to choose shoalmates. Generally they prefer larger shoals, shoalmates of their own species, shoalmates similar in size and appearance to themselves, healthy fish, and kin (when recognised). The "oddity effect" posits that any shoal member that stands out in appearance will be preferentially targeted by predators. This may explain why fish prefer to shoal with individuals that resemble them. The oddity effect would thus tend to homogenise shoals.<ref>{{cite journal |vauthors= Snekser JL, Ruhl N, Bauer K, McRobert SP |year= 2010 |title= The Influence of Sex and Phenotype on Shoaling Decisions in Zebrafish |url= http://comparativepsychology.org/2010ijcpissue1/05.Snekser_etal_Final.pdf |journal= International Journal of Comparative Psychology |volume= 23 |pages= 70–81 |doi= 10.46867/IJCP.2010.23.01.04 |url-status= dead |archive-url= https://web.archive.org/web/20110725190329/http://comparativepsychology.org/2010ijcpissue1/05.Snekser_etal_Final.pdf |archive-date= 2011-07-25}}</ref>

One puzzling aspect of shoal selection is how a fish can choose to join a shoal of animals similar to themselves, given that it cannot know its own appearance. Experiments with [[zebrafish]] have shown that shoal preference is a learned ability, not innate. A zebrafish tends to associate with shoals that resemble shoals in which it was reared, a form of [[imprinting (psychology)|imprinting]].<ref>{{cite journal |vauthors=Engeszer RE, Ryan MJ, Parichy DM |year= 2004 |title= Learned Social Preference in Zebrafish |url= http://www.sbs.utexas.edu/ryan/Publications/2004/2004CurrBiol14%20881.pdf |journal= Current Biology |volume= 14 |issue= 10 |pages= 881–884 |doi= 10.1016/j.cub.2004.04.042 |pmid= 15186744|s2cid= 18741014 |doi-access= free |bibcode= 2004CBio...14..881E }}</ref>

Other open questions of shoaling behaviour include identifying which individuals are responsible for the direction of shoal movement. In the case of [[fish migration|migratory]] movement, most members of a shoal seem to know where they are going. In the case of foraging behaviour, captive shoals of [[golden shiner]] (a kind of [[minnow]]) are led by a small number of experienced individuals who knew when and where food was available.<ref>{{cite journal |doi=10.1006/anbe.1999.1314 |author=Reebs, S.G. |title=Can a minority of informed leaders determine the foraging movements of a fish shoal? |journal=Animal Behaviour |volume=59 |issue=2 |pages=403–9 |year=2000 |pmid=10675263|s2cid=4945309 }}</ref>

Radakov estimated herring schools in the North Atlantic can occupy up to {{convert|4.8|km3}} with fish densities between 0.5 and 1.0 fish/cubic metre, totalling several billion fish in one school.<ref>Radakov DV (1973) ''Schooling in the ecology of fish.'' Israel Program for Scientific Translation, translated by Mill H. Halsted Press, New York. {{ISBN|978-0-7065-1351-6}}</ref>

{{See also|Eel life history}}
* Partridge BL (1982) [https://web.archive.org/web/20110703035553/https://137.146.28.140/biology/BI358j/Readings/Partridge%201982.pdf "The structure and function of fish schools"] ''Scientific American'', June:114–123.
* {{cite journal |vauthors= Parrish JK, Viscido SV, Grunbaum D |year= 2002 |title= Self-Organized Fish Schools: An Examination of Emergent Properties |url= http://faculty.washington.edu/random/Reprints/Parrishetal02.pdf |archive-url= https://web.archive.org/web/20060911165104/http://faculty.washington.edu/random/Reprints/Parrishetal02.pdf |url-status= dead |archive-date= 11 September 2006 |journal= Biol. Bull. |volume= 202 |issue= 3 |pages= 296–305 |doi= 10.2307/1543482 |pmid= 12087003 |jstor= 1543482 |citeseerx= 10.1.1.116.1548 |s2cid= 377484 }}