{{Short description|Fish integument}}
[[File:Eldon's galaxias (Galaxias eldoni) - closeup of skin.jpg|right|thumb|upright=1|A closeup of the skin on an Eldon's galaxias]] The '''slime coat''' (also '''fish slime''', '''mucus layer''' or '''slime layer''') is the coating of mucus covering the body of all fish. An important part of fish anatomy, it serves many functions, depending on species, ranging from locomotion, care and feeding of offspring, to resistance against diseases and parasites.<ref name="Note">{{Cite journal|last=Jakowska|first=Sophie|date=1963|title=Mucus Secretion in Fish—a Note*|url=https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1749-6632.1963.tb16658.x|journal=Annals of the New York Academy of Sciences|language=en|volume=106|issue=2|pages=458–462|doi=10.1111/j.1749-6632.1963.tb16658.x|pmid=13964523|bibcode=1963NYASA.106..458J|s2cid=13445731|issn=1749-6632|url-access=subscription}}</ref>
The mucin making up the slime coat is secreted by goblet cells in the fish's epidermis.<ref>{{Cite web|last=Kraugerud|first=Reidun Lilleholt|title=Fish skin and its protective properties|url=https://nofima.no/en/worth-knowing/fish-skin-and-its-protective-properties/|access-date=2021-09-13|website=Nofima|date=15 January 2021 |language=en-US}}</ref> The slime contains a variety of antimicrobial peptides and other antimicrobial components such as lysozyme and C-reactive protein.<ref name="AMPs">{{Cite journal|last1=Rakers|first1=Sebastian|last2=Niklasson|first2=Lars|last3=Steinhagen|first3=Dieter|last4=Kruse|first4=Charli|last5=Schauber|first5=Jürgen|last6=Sundell|first6=Kristina|last7=Paus|first7=Ralf|date=2013|title=Antimicrobial Peptides (AMPs) from Fish Epidermis: Perspectives for Investigative Dermatology|journal=Journal of Investigative Dermatology|volume=133|issue=5|pages=1140–1149|doi=10.1038/jid.2012.503|pmid=23407389|issn=0022-202X|doi-access=free}}</ref><ref>{{Cite journal|last1=Tiralongo|first1=Francesco|last2=Messina|first2=Giuseppina|last3=Lombardo|first3=Bianca Maria|last4=Longhitano|first4=Lucia|last5=Li Volti|first5=Giovanni|last6=Tibullo|first6=Daniele|date=2020|title=Skin Mucus of Marine Fish as a Source for the Development of Antimicrobial Agents|journal=Frontiers in Marine Science|volume=7|language=English|doi=10.3389/fmars.2020.541853|issn=2296-7745|doi-access=free}}</ref> It contains mycosporine-like amino acids to protect from ultraviolet radiation.
== Locomotion == The slime coat of some fish aids in more efficient swimming by reducing drag,<ref>{{Citation|last=Hoyt|first=J. W.|title=Hydrodynamic Drag Reduction Due to Fish Slimes|date=1975|url=https://doi.org/10.1007/978-1-4757-1326-8_13|work=Swimming and Flying in Nature: Volume 2|pages=653–672|editor-last=Wu|editor-first=Theodore Y.-T.|place=Boston, MA|publisher=Springer US|language=en|doi=10.1007/978-1-4757-1326-8_13|isbn=978-1-4757-1326-8|access-date=2021-09-12|editor2-last=Brokaw|editor2-first=Charles J.|editor3-last=Brennen|editor3-first=Christopher|url-access=subscription}}</ref><ref>{{Cite journal|last1=Rosen|first1=Moe Wm|last2=Cornford|first2=Neri E.|date=1971|title=Fluid Friction of Fish Slimes|url=https://www.nature.com/articles/234049a0|journal=Nature|language=en|volume=234|issue=5323|pages=49–51|doi=10.1038/234049a0|bibcode=1971Natur.234...49R|s2cid=4268462|issn=1476-4687|url-access=subscription}}</ref> attributed to the Toms effect.<ref>{{Cite journal|last=Daniel|first=Thomas L.|date=1981-06-01|title=Fish mucus: in situ measurements of polymer drag reduction|url=https://www.biodiversitylibrary.org/part/14672|journal=The Biological Bulletin|volume=160|issue=3|pages=376–382|doi=10.2307/1540846|jstor=1540846|issn=0006-3185|via=Biodiversity Heritage Library}}</ref><ref>{{Cite web|title=Slime Reduces Drag — Biological Strategy|url=https://asknature.org/strategy/slime-reduces-drag/|access-date=2021-09-12|website=asknature.org|language=en-US|publisher=Biomimicry Institute}}</ref> Slime can reduce the friction experienced by the fish by up to 65%.<ref>{{Cite web|last=Ramel|first=Gordon|date=2020-03-24|title=Fish Locomotion & Movement 101: How Fish Swim Explained|url=https://www.earthlife.net/fish/locomotion.html|access-date=2021-09-12|website=Earth Life|language=en-US}}</ref> Generally, the faster the fish, the greater reduction in drag provided by the slime, but there are a few exceptions.<ref name="Blake">{{Cite book|last=Blake|first=Robert W.|url=https://books.google.com/books?id=M7E8AAAAIAAJ|title=Fish Locomotion|date=1983-05-26|publisher=CUP Archive|isbn=978-0-521-24303-2|pages=66–68|language=en}}</ref>
In schooling fish, slime shed by leading fish is thought to provide a hydrodynamic benefit to following fish.<ref name="Eco-Etho">{{Cite book|last=Domenici|first=Paolo|url=https://www.journals.uchicago.edu/doi/10.1086/656882|title=Fish Locomotion: An Eco-ethological Perspective|date=2010-01-01|publisher=CRC Press|isbn=978-1-000-73803-2|page=100|language=en|doi=10.1086/656882}}</ref>
== As a defensive adaptation == The slime coat of reef fish contains mycosporine-like amino acids (MAAs) which protect the fish from sun damage by absorbing radiation. The greatest number of MAAs is found on the dorsal side of the fish, which is exposed to more radiation.<ref>{{Cite journal|last1=Braun|first1=C.|last2=Reef|first2=R.|last3=Siebeck|first3=U. E.|date=2016-07-01|title=Ultraviolet absorbing compounds provide a rapid response mechanism for UV protection in some reef fish|url=https://www.sciencedirect.com/science/article/pii/S1011134415302219|journal=Journal of Photochemistry and Photobiology B: Biology|language=en|volume=160|pages=400–407|doi=10.1016/j.jphotobiol.2016.04.020|pmid=27162066 |bibcode=2016JPPB..160..400B |issn=1011-1344|url-access=subscription}}</ref> Animals cannot synthesize MAAs, requiring fish to sequester them from their diet.<ref>{{Cite journal|last1=Eckes|first1=Maxi J.|last2=Siebeck|first2=Ulrike E.|last3=Dove|first3=Sophie|last4=Grutter|first4=Alexandra S.|date=2008-01-17|title=Ultraviolet sunscreens in reef fish mucus|url=https://www.int-res.com/abstracts/meps/v353/p203-211/|journal=Marine Ecology Progress Series|language=en|volume=353|pages=203–211|doi=10.3354/meps07210|bibcode=2008MEPS..353..203E |issn=0171-8630|doi-access=free}}</ref>
Under water, fish are exposed to a greater number of microorganisms than animals whose skin is exposed mainly to air. In the absence of a stratum corneum, the slime coat serves to protect the fish from attack from harmful microorganisms.<ref name="Lectin">{{Cite journal|last1=Tsutsui|first1=Shigeyuki|last2=Komatsu|first2=Yukie|last3=Sugiura|first3=Takaya|last4=Araki|first4=Kyosuke|last5=Nakamura|first5=Osamu|date=2011-11-01|title=A unique epidermal mucus lectin identified from catfish (Silurus asotus): first evidence of intelectin in fish skin slime|url=https://doi.org/10.1093/jb/mvr085|journal=The Journal of Biochemistry|volume=150|issue=5|pages=501–514|doi=10.1093/jb/mvr085|pmid=21757471|issn=0021-924X|url-access=subscription|doi-access=free}}</ref> This is chiefly done by sloughing off microbes which become trapped in the slime coat, but the slime coat contains antimicrobial peptides and other defensive properties such as lysozyme and C-reactive protein.<ref name="Major determinant">{{Cite journal|last1=Dash|first1=S.|last2=Das|first2=S. K.|last3=Samal|first3=J.|last4=Thatoi|first4=H. N.|date=2018|title=Epidermal mucus, a major determinant in fish health: a review|journal=Iranian Journal of Veterinary Research|volume=19|issue=2|pages=72–81|issn=1728-1997|pmc=6056142|pmid=30046316}}</ref>
Parrotfish create extra mucus during sleep which covers their bodies in a cocoon-like structure. It protects them from predators and parasites by masking their scent and providing a physical barrier against them.<ref>{{Cite web|title=Mucous Cocoon Protects From Predators — Biological Strategy|url=https://asknature.org/strategy/mucous-cocoon-protects-from-predators-2/|access-date=2021-09-28|website=asknature.org|language=en-US}}</ref>
[[File:Hagfish Slime Predator Deterrence.jpg|right|thumb|350px|A seal shark (top, a–c) and an Atlantic wreckfish (bottom, d–f) each attempt to prey on a hagfish.]] The slime of the hagfish is unique due to its volume and dilution. In these fish it serves as an anti-predator adaptation: when grabbed by a predator fish, the hagfish ejects copious amounts of slime into the predator's mouth, causing the predator to gag and flare its gills, releasing the hagfish and moving away.<ref name="Hag1">{{Cite journal|last1=Zintzen|first1=Vincent|last2=Roberts|first2=Clive D.|last3=Anderson|first3=Marti J.|last4=Stewart|first4=Andrew L.|last5=Struthers|first5=Carl D.|last6=Harvey|first6=Euan S.|date=2011-10-27|title=Hagfish predatory behaviour and slime defence mechanism|journal=Scientific Reports|language=en|volume=1|issue=1|pages=131|doi=10.1038/srep00131|pmid=22355648|pmc=3216612|bibcode=2011NatSR...1..131Z|issn=2045-2322}}</ref>
== Human importance == In pisciculture and fishkeeping, the slime coat is important to the health of fish,<ref>{{Cite web |last1=Green |first1=Christopher |last2=Haukenes |first2=Alf |date=September 2015 |title=The Role of Stress in Fish Disease |url=https://fisheries.tamu.edu/files/2019/01/SRAC_0474.pdf |publisher=TAMU}}</ref> particularly during transport which can cause damage to it.<ref>{{Cite journal |last=Harmon |first=Todd S. |date=March 2009 |title=Methods for reducing stressors and maintaining water quality associated with live fish transport in tanks: a review of the basics |url=https://onlinelibrary.wiley.com/doi/10.1111/j.1753-5131.2008.01003.x |journal=Reviews in Aquaculture |language=en |volume=1 |issue=1 |pages=58–66 |doi=10.1111/j.1753-5131.2008.01003.x|bibcode=2009RvAq....1...58H |url-access=subscription }}</ref> High ammonia levels in the water can also cause damage to the slime coat.<ref>{{Cite journal |last1=Ogbonna F. |first1=Joel |last2=Chinomso A. |first2=Amajuoyi |date=February 2010 |title=DETERMINATION OF THE CONCENTRATION OF AMMONIA THAT COULD HAVE LETHAL EFFECT ON FISH POND|url=https://www.researchgate.net/publication/304929519 |journal=ARPN Journal of Engineering and Applied Sciences |volume=5 |issue=2}}</ref>
The antimicrobial properties of fish slime have been studied as an alternative to antibiotic drugs to address antibiotic resistance.<ref>{{Cite journal |last1=Kuppulakshmi |first1=C. |last2=Prakash |first2=M. |last3=Gunasekaran |first3=G. |last4=Manimegalai |first4=G. |last5=Sarojini |first5=S. |date=2008 |title=Antibacterial properties of fish mucus from Channa punctatus and Cirrhinus mrigala |journal=European Review for Medical and Pharmacological Sciences |volume=12 |issue=3 |pages=149–153 |issn=1128-3602 |pmid=18700685}}</ref><ref>{{Cite journal |last1=Hussain |first1=Ahmed |last2=Sachan |first2=Shashwati Ghosh |date=2023-03-20 |title=Fish Epidermal Mucus as a Source of Diverse Therapeutical Compounds |url=https://doi.org/10.1007/s10989-023-10505-6 |journal=International Journal of Peptide Research and Therapeutics |language=en |volume=29 |issue=3 |pages=36 |doi=10.1007/s10989-023-10505-6 |issn=1573-3904 |pmc=10026197 |pmid=36968337}}</ref>
== See also == * Snail slime
== References == {{Reflist}}
== Further reading == * {{Cite book|last1=Wainwright|first1=Dylan K.|chapter=Mucus Matters: The Slippery and Complex Surfaces of Fish|date=2017|chapter-url=https://www.people.fas.harvard.edu/~glauder/reprints_unzipped/Wainwright.Lauder.Mucus.Matters.2018.pdf|title=Functional Surfaces in Biology III: Diversity of the Physical Phenomena|pages=223–246|editor-last=Gorb|editor-first=Stanislav N.|series=Biologically-Inspired Systems|publisher=Springer, Cham|language=en|doi=10.1007/978-3-319-74144-4_10|isbn=978-3-319-74144-4|access-date=2021-09-13|last2=Lauder|first2=George V.|volume=10 |editor2-last=Gorb|editor2-first=Elena V.}}
Category:Fish anatomy Category:Integumentary system Category:Fish reproduction Category:Fish health Category:Fishkeeping