Slime coat

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 to disease and parasites.[1]

A closeup of the skin on an Eldon's galaxias

The mucin making up the slime coat is secreted by goblet cells in the fish's epidermis.[2] The slime contains a variety of antimicrobial peptides and other antimicrobial components such as lysozyme and C-reactive protein.[3][4] 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,[5][6] attributed to the Toms effect.[7][8] Slime can reduce the friction experienced by the fish by up to 65%.[9] Generally, the faster the fish, the greater reduction in drag provided by the slime, but there are a few exceptions.[10]

In schooling fish, slime shed by leading fish is thought to provide a hydrodynamic benefit to following fish.[11]

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.[12] Animals cannot synthesize MAAs, requiring fish to sequester them from their diet.[13]

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.[14] 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.[15]

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.[16]

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.[17]

Human importance

In pisciculture and fishkeeping, the slime coat is important to the health of fish,[18] particularly during transport which can cause damage to it.[19] High ammonia levels in the water can also cause damage to the slime coat.[20]

The antimicrobial properties of fish slime have been studied as an alternative to antibiotic drugs to address antibiotic resistance.[21][22]

See also

References
  1. Jakowska, Sophie (1963). "Mucus Secretion in Fish—a Note*". Annals of the New York Academy of Sciences. 106 (2): 458–462. Bibcode:1963NYASA.106..458J. doi:10.1111/j.1749-6632.1963.tb16658.x. ISSN 1749-6632. PMID 13964523. S2CID 13445731.
  2. Kraugerud, Reidun Lilleholt (15 January 2021). "Fish skin and its protective properties". Nofima. Retrieved 2021-09-13.
  3. Rakers, Sebastian; Niklasson, Lars; Steinhagen, Dieter; Kruse, Charli; Schauber, Jürgen; Sundell, Kristina; Paus, Ralf (2013). "Antimicrobial Peptides (AMPs) from Fish Epidermis: Perspectives for Investigative Dermatology". Journal of Investigative Dermatology. 133 (5): 1140–1149. doi:10.1038/jid.2012.503. ISSN 0022-202X. PMID 23407389.
  4. Tiralongo, Francesco; Messina, Giuseppina; Lombardo, Bianca Maria; Longhitano, Lucia; Li Volti, Giovanni; Tibullo, Daniele (2020). "Skin Mucus of Marine Fish as a Source for the Development of Antimicrobial Agents". Frontiers in Marine Science. 7. doi:10.3389/fmars.2020.541853. ISSN 2296-7745.
  5. Hoyt, J. W. (1975), Wu, Theodore Y.-T.; Brokaw, Charles J.; Brennen, Christopher (eds.), "Hydrodynamic Drag Reduction Due to Fish Slimes", Swimming and Flying in Nature: Volume 2, Boston, MA: Springer US, pp. 653–672, doi:10.1007/978-1-4757-1326-8_13, ISBN 978-1-4757-1326-8, retrieved 2021-09-12
  6. Rosen, Moe Wm; Cornford, Neri E. (1971). "Fluid Friction of Fish Slimes". Nature. 234 (5323): 49–51. Bibcode:1971Natur.234...49R. doi:10.1038/234049a0. ISSN 1476-4687. S2CID 4268462.
  7. Daniel, Thomas L. (1981-06-01). "Fish mucus: in situ measurements of polymer drag reduction". The Biological Bulletin. 160 (3): 376–382. doi:10.2307/1540846. ISSN 0006-3185. JSTOR 1540846 – via Biodiversity Heritage Library.
  8. "Slime Reduces Drag — Biological Strategy". asknature.org. Biomimicry Institute. Retrieved 2021-09-12.
  9. Ramel, Gordon (2020-03-24). "Fish Locomotion & Movement 101: How Fish Swim Explained". Earth Life. Retrieved 2021-09-12.
  10. Blake, Robert W. (1983-05-26). Fish Locomotion. CUP Archive. pp. 66–68. ISBN 978-0-521-24303-2.
  11. Domenici, Paolo (2010-01-01). Fish Locomotion: An Eco-ethological Perspective. CRC Press. p. 100. doi:10.1086/656882. ISBN 978-1-000-73803-2.
  12. Braun, C.; Reef, R.; Siebeck, U. E. (2016-07-01). "Ultraviolet absorbing compounds provide a rapid response mechanism for UV protection in some reef fish". Journal of Photochemistry and Photobiology B: Biology. 160: 400–407. doi:10.1016/j.jphotobiol.2016.04.020. ISSN 1011-1344. PMID 27162066.
  13. Eckes, Maxi J.; Siebeck, Ulrike E.; Dove, Sophie; Grutter, Alexandra S. (2008-01-17). "Ultraviolet sunscreens in reef fish mucus". Marine Ecology Progress Series. 353: 203–211. Bibcode:2008MEPS..353..203E. doi:10.3354/meps07210. ISSN 0171-8630.
  14. Tsutsui, Shigeyuki; Komatsu, Yukie; Sugiura, Takaya; Araki, Kyosuke; Nakamura, Osamu (2011-11-01). "A unique epidermal mucus lectin identified from catfish (Silurus asotus): first evidence of intelectin in fish skin slime". The Journal of Biochemistry. 150 (5): 501–514. doi:10.1093/jb/mvr085. ISSN 0021-924X. PMID 21757471.
  15. Dash, S.; Das, S. K.; Samal, J.; Thatoi, H. N. (2018). "Epidermal mucus, a major determinant in fish health: a review". Iranian Journal of Veterinary Research. 19 (2): 72–81. ISSN 1728-1997. PMC 6056142. PMID 30046316.
  16. "Mucous Cocoon Protects From Predators — Biological Strategy". asknature.org. Retrieved 2021-09-28.
  17. Zintzen, Vincent; Roberts, Clive D.; Anderson, Marti J.; Stewart, Andrew L.; Struthers, Carl D.; Harvey, Euan S. (2011-10-27). "Hagfish predatory behaviour and slime defence mechanism". Scientific Reports. 1 (1): 131. Bibcode:2011NatSR...1E.131Z. doi:10.1038/srep00131. ISSN 2045-2322. PMC 3216612. PMID 22355648.
  18. Green, Christopher; Haukenes, Alf (September 2015). "The Role of Stress in Fish Disease" (PDF). TAMU.
  19. Harmon, Todd S. (March 2009). "Methods for reducing stressors and maintaining water quality associated with live fish transport in tanks: a review of the basics". Reviews in Aquaculture. 1 (1): 58–66. doi:10.1111/j.1753-5131.2008.01003.x.
  20. Ogbonna F., Joel; Chinomso A., Amajuoyi (February 2010). "DETERMINATION OF THE CONCENTRATION OF AMMONIA THAT COULD HAVE LETHAL EFFECT ON FISH POND". ARPN Journal of Engineering and Applied Sciences. 5 (2).
  21. Kuppulakshmi, C.; Prakash, M.; Gunasekaran, G.; Manimegalai, G.; Sarojini, S. (2008). "Antibacterial properties of fish mucus from Channa punctatus and Cirrhinus mrigala". European Review for Medical and Pharmacological Sciences. 12 (3): 149–153. ISSN 1128-3602. PMID 18700685.
  22. Hussain, Ahmed; Sachan, Shashwati Ghosh (2023-03-20). "Fish Epidermal Mucus as a Source of Diverse Therapeutical Compounds". International Journal of Peptide Research and Therapeutics. 29 (3): 36. doi:10.1007/s10989-023-10505-6. ISSN 1573-3904. PMC 10026197. PMID 36968337.

Further reading
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