Milt

Quality 0.50 · 3 views · Updated 2 months ago

Fish seminal fluid and sacs

title: "Milt" type: doc version: 1 created: 2026-02-28 author: "Wikipedia contributors" status: active scope: public tags: ["reproduction-in-animals", "fish-products", "semen", "fish-reproduction", "offal", "cuts-of-fish"] description: "Fish seminal fluid and sacs" topic_path: "general/reproduction-in-animals" source: "https://en.wikipedia.org/wiki/Milt" license: "CC BY-SA 4.0" wikipedia_page_id: 0 wikipedia_revision_id: 0

::summary Fish seminal fluid and sacs ::

::figure[src="https://upload.wikimedia.org/wikipedia/commons/1/18/Milt_collection.jpg" caption="Collecting [[Chinook salmon]] milt at a [[USFWS]] [[hatchery"] ::

Milt is the seminal fluid of fish, mollusks, and certain other water-dwelling animals. They reproduce by spraying this fluid, which contains the sperm, onto roe (fish eggs). It can also refer to the sperm sacs or testes that contain the semen.

Milt (sometimes spelled melt) also refers to soft roe, the male genitalia of fish when they contain sperm, used as food. Many cultures eat milt, often fried, though not usually as a dish by itself. As a food item, milt is farmed year-round in nitrogen tanks, through hormone induction or photoperiod control.

Production

Production of milt may be affected by external stimuli. Goldfish are known to produce more milt when isolated from other males in their group, but will continue to produce high levels even when exposed to the scent of an unfamiliar male, suggesting that milt production is affected by close contact to rival males. Milt production is also stimulated by the scent of a female fish. Milt itself may contain pheromones that attract ovulating females. ::figure[src="https://upload.wikimedia.org/wikipedia/commons/0/01/Spawning_collecting_milt_for_broodstock_lake_trout_(48789174696).jpg" caption="Milt from a lake trout being used to fertilize eggs"] ::

Intersex fish are less likely to release milt, or may fail to produce milt at all, due to their sperm ducts being blocked. Even when intersex fish do produce milt, the sperm density is lower than normal, and the sperm that is present typically has less motility than normal. Triploid fish can sire offpring, but said offspring have low hatch rates and high mortality rates. For this reason, some hatcheries may intentionally produce triploid fish to keep them from hybridizing or competing with native fish.

Chemical composition of milt varies slightly by species. Herring milt is 82.5% water, 2% fat, 16.7% protein, and 2% ash for fish with 21% milt. Cod milt is 82% water, 1.1% fat, 14.5% protein, and 1.8% ash.

Use in captive breeding

::figure[src="https://upload.wikimedia.org/wikipedia/commons/b/b5/Salmon_Milt_DIPAC_WC7.jpg" caption="Milt collection at an Alaskan hatchery"] ::

At fish hatcheries, workers manually squeeze milt out of male fish, then use the milt to fertilize harvested eggs. This can be done to many fish while alive, and afterwards the fish can be released. Pacific salmon hatcheries are an exception; the fish, returning from migration, are killed via a guillotine and then the milt is poured over eggs, either by squeezing the male over them or by putting the milt in a dropper and squeezing it in.

After collection, milt may be refrigerated for brief periods of time to increase sperm motility. Pacu milt, for example, will still have live sperm after 8 hours, and the motility will be higher compared to milt stored at room temperature. This is not true of all species, however; the longer the milt of the steelhead trout is stored, the higher the mortality rate of the hatchlings it produces.

Milt removed from dead fish can still be fertile hours after the fish's death. A blacktail redhorse's milt, for one, is still fertile an hour after the fish has died; chinook salmon milt, for another, is still fertile up to five hours after the fish has died. Milt is still fertile even if the fish it came from was killed by piscicide.

Milt as food

Though many North Americans find the consumption of milt taboo, it is popular in many Asian and European cuisines, and has been called "the male counterpart to caviar".

Asian cuisine

European cuisine

File:Shirako gunkanmaki.jpg|Japanese shirako (cod milt) gunkanmaki File:Smelt milt.jpg|Smelt milt File:Alaska pollack liver roe milt.jpg|Alaska pollock's liver, roe, and milt

Other uses

Milt is highly absorbent of rare earth elements such as neodymium and iron. The heavier the rare earth element, the higher its affinity for milt. Because of this, it has been proposed as an environmentally-friendly way to recover rare earth elements from waste.

References

References

  1. (4 August 2018). "Two quick recipes for Melts (aka soft herring roes)".
  2. (1877). ["Lochandhu: A Tale of the Eighteenth Century"]({{Google books). James Watson.
  3. "Roe (food)".
  4. (2019). "Gases in Agro-food processes".
  5. Stacey, Norm. (December 2001). "Milt production in goldfish: regulation by multiple social stimuli". [[Comparative Biochemistry and Physiology Part C: Toxicology & Pharmacology]].
  6. Fraser, Jane. (1 October 2002). "Isolation increases milt production in goldfish". [[Journal of Experimental Zoology]].
  7. Scott, Anne M.. (9 July 2019). "Spremine in semen of male sea lamprey acts as a sex pheromone". [[PLOS One]].
  8. Harris, Catherine A.. (8 October 2010). "The Consequences of Feminization in Breeding Groups of Wild Fish". Environmental Health Perspectives.
  9. Jobling, Susan. (2002). "Wild intersex roach (Rotilus rotilus) have reduced fertility.". [[Biology of Reproduction]].
  10. Feindel, Nathaniel J. (20 July 2010). "Competitive spawning success and fertility of triploid male Atlantic cod Gadus morhua". Aquaculture Environment Interactions.
  11. Ewing, Rebekah. (9 November 2023). "Spawning Triploid Trout to Enhance Recreation".
  12. Batista, I. (2007). "Maximising the Value of Marine By-Products".
  13. "DEC Fish Hatchery FAQs".
  14. Mitchell, Hannah. (22 June 2022). "4 million mouths to feed: Life at the Dworshak Fish Hatchery".
  15. Schick, Tony. (24 May 2022). "The U.S. has spent more than $2B on a plan to save salmon. The fish are vanishing anyway.".
  16. Spica, L.N.. (5 June 2024). "Viability duration of pacu (Piaractus mesopotamicus) milt stored under refrigeration". Brazilian Journal of Biology.
  17. Smith, Richard T. (15 October 1943). "Experiments with the Spermatozoa of the Steelhead Trout, Salmo gairdnerii gairdnerii and the Chinook Salmon, Oncorhynchus tschawytscha". Copeia.
  18. Garth, W.A.. (2 June 1952). "Fertilization of eggs from a catostomid fish, Moxostoma poecilurum, killed by rotenone.". Copeia.
  19. Caterucci, Christina. (18 April 2025). "Bad Seed".
  20. Theriault Boots, Michelle. (2 February 2015). "Alaska fish processors chase Japanese market for an unusual product-cod semen".
  21. Corporation, Zojirushi America. (2018-05-11). "An Acquired Taste of Japan – Shirako".
  22. "What is Milt: Dicovering the Weird Ingredient Made of Tuna Sperm".
  23. Kirshenblatt-Gimblett, Barbara. (12 April 2024). "An Ashkenazi delicacy made of fish sperm".
  24. Takahashi, Yokio. (9 December 2014). "Recovery and Separation of Rare Earth Elements Using Salmon Milt". [[PLOS One]].

::callout[type=info title="Wikipedia Source"] This article was imported from Wikipedia and is available under the Creative Commons Attribution-ShareAlike 4.0 License. Content has been adapted to SurfDoc format. Original contributors can be found on the article history page. ::

reproduction-in-animalsfish-productssemenfish-reproductionoffalcuts-of-fish