Milt

Production of milt may be affected by external stimuli. Goldfish are known to produce more milt when isolated from other males in their group,{{Cite journal |last=Stacey |first=Norm |date=December 2001 |title=Milt production in goldfish: regulation by multiple social stimuli |journal=Comparative Biochemistry and Physiology Part C: Toxicology and Pharmacology |volume=130 |issue=4 |pages=467–476}}{{Cite journal |last=Fraser |first=Jane |date=1 October 2002 |title=Isolation increases milt production in goldfish |journal=Journal of Experimental Zoology |volume=293 |issue=5 |pages=511–524}} 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 pheremones that attract ovulating females.{{Cite journal |last=Scott |first=Anne M. |date=9 July 2019 |title=Spremine in semen of male sea lamprey acts as a sex pheromone |url=https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.3000332 |journal=PLOS One |via=}}

File:Spawning collecting milt for broodstock lake trout (48789174696).jpg

Intersex fish are less likely to release milt, or may fail to produce milt at all, due to their sperm ducts being blocked.{{Cite journal |last=Harris |first=Catherine A. |date=8 October 2010 |title=The Consequences of Feminization in Breeding Groups of Wild Fish |url=https://ehp.niehs.nih.gov/doi/full/10.1289/ehp.1002555 |journal=Environmental Health Perspectives |volume=119 |issue=3 |pages=306–311}} Even when intersex fish do produce milt, the sperm density is lower than normal, and the sperm that is present typiclaly has less motility than normal.{{Cite journal |last=Jobling |first=Susan |date=2002 |title=Wild intersex roach (Rotilus rotilus) have reduced fertility. |journal=Biology of Reproduction |volume=67 |issue=2 |pages=515–524}} Triploid fish can sire offpring, but said offspring have low hatch rates and high mortality rates.{{Cite journal |last=Feindel |first=Nathaniel J |date=20 July 2010 |title=Competitive spawning success and fertility of triploid male Atlantic cod Gadus morhua |journal=Aquaculture Environment Interactions |volume=1 |issue=1 |pages=47–55}} For this reason, some hatcheries may intentionally produce triploid fish to keep them from hybridizing or competing with native fish.{{Cite web |last=Ewing |first=Rebekah |date=9 November 2023 |title=Spawning Triploid Trout to Enhance Recreation |url=https://www.fws.gov/story/2023-11/triploid-trout |website=U.S. Fish and Wildlife Service}}

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.{{cite book |last=Batista |first=I |title=Maximising the Value of Marine By-Products |date=2007 |isbn=978-1-84569-013-7 |pages=171–195 |chapter=By-catch, underutilized species and underutilized fish parts as food ingredients |doi=10.1533/9781845692087.2.171 |chapter-url=https://www.sciencedirect.com/science/article/abs/pii/B9781845690137500089}}

File:Salmon Milt DIPAC WC7.jpg

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.{{Cite web |title=DEC Fish Hatchery FAQs |url=https://dec.ny.gov/things-to-do/freshwater-fishing/hatcheries/faqs |website=New York Department of Environmental Conservation}} Pacific salmon hatcheries are an exception; the fish, returning from migration,{{Cite web |last=Mitchell |first=Hannah |date=22 June 2022 |title=4 million mouths to feed: Life at the Dworshak Fish Hatchery |url=https://www.army.mil/article/257806/4_million_mouths_to_feed_life_at_the_dworshak_national_fish_hatchery |website=U.S. Army}} 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.{{Cite web |last=Schick |first=Tony |date=24 May 2022 |title=The U.S. has spent more than $2B on a plan to save salmon. The fish are vanishing anyway. |url=https://www.opb.org/article/2022/05/24/pacific-northwest-federal-salmon-hatcheries-declining-returns/ |website=Oregon Public Broadcasting}}

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.{{Cite journal |last=Spica |first=L.N. |date=5 June 2024 |title=Viability duration of pacu (Piaractus mesopotamicus) milt stored under refrigeration |journal=Brazilian Journal of Biology |volume=84}} 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.{{Cite journal |last=Smith |first=Richard T |date=15 October 1943 |title=Experiments with the Spermatozoa of the Steelhead Trout, Salmo gairdnerii gairdnerii and the Chinook Salmon, Oncorhynchus tschawytscha |journal=Copeia |volume=1943 |issue=3 |pages=167}}

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;{{Cite journal |last=Garth |first=W.A. |date=2 June 1952 |title=Fertilization of eggs from a catostomid fish, Moxostoma poecilurum, killed by rotenone. |journal=Copeia |volume=1952 |issue=1 |pages=43}} 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.

Though many North Americans find the consumption of milt taboo,{{Cite web |last=Caterucci |first=Christina |date=18 April 2025 |title=Bad Seed |url=https://slate.com/life/2025/04/eggs-fish-dinner-sperm-eat-milt.html |website=Slate}} it is popular in many Asian and European cuisines, and has been called "the male counterpart to caviar".{{Cite web |last=Theriault Boots |first=Michelle |date=2 February 2015 |title=Alaska fish processors chase Japanese market for an unusual product-cod semen |url=https://www.adn.com/alaska-news/article/cod-semen-anyone-alaska-fish-byproduct-unlikely-culinary-following-japan/2015/02/02/ |website=Anchorage Daily News}}

• In Indonesian cuisine, the milt (called {{lang|id|telur ikan}} {{gloss|fish egg}}) of snakehead and snapper is usually made into kari or woku.
• In Japanese cuisine, the testes ({{lang|ja|白子}} {{lang|ja-latn|shirako}} {{gloss|white children}}) of cod ({{lang|ja-latn|tara}}), anglerfish ({{lang|ja-latn|ankō}}), salmon ({{lang|ja-latn|sake}}), squid ({{lang|ja-latn|ika}}) and pufferfish (fugu) are eaten.{{Cite web |last=Corporation |first=Zojirushi America |date=2018-05-11 |title=An Acquired Taste of Japan – Shirako |url=https://www.zojirushi.com/blog/an-acquired-taste-of-japan-shirako/ |access-date=2025-04-27 |website=Zojirushi Food & Culture Blog |language=en-US}}
• In Korean cuisine, the milt ({{lang|ko|이리}} {{lang|ko-latn|iri}}) of Alaska pollock, cod, blackmouth angler, bogeo, and sea bream are eaten.

• In Romanian cuisine, the milt of carp and other fresh water fish is called {{lang|ro|lapți}} (from the Latin word lactes) and is usually fried.
• In Russian cuisine, herring milt ({{lang|ru|молока}}, {{lang|ru-latn|moloka}}) is pickled the same way as the rest of the fish, but eaten separately, sometimes combined with pickled herring roe. Various whitefish soft roes are usually consumed fried and it is an inexpensive everyday dish.
• In Sicilian cuisine, the milt of tuna is called {{lang|scn|lattume}} and is used as a typical pasta topping.{{Cite web |title=What is Milt: Dicovering the Weird Ingredient Made of Tuna Sperm |url=https://www.finedininglovers.com/explore/articles/curious-delicacies-getting-know-milt |access-date=2025-04-27 |website=www.finedininglovers.com |language=en}}
• In British cuisine, cod soft roes are a traditional dish, usually fried in butter and spread on toast.
• In Czech cuisine, the milt of common carp called {{lang|cs|mlíčí}} (from the Czech word mléko - milk) is often used in a fish soup served on Christmas Eve dinner.
• In Ashkenazi Jewish cuisine, kratsborscht is a sauce made from milt.{{Cite web |last=Kirshenblatt-Gimblett |first=Barbara |date=12 April 2024 |title=An Ashkenazi delicacy made of fish sperm |url=https://forward.com/yiddish-world/601750/ashkenazi-delicacy-fish-sperm-herring/ |website=Forward}}

File:Shirako gunkanmaki.jpg|Japanese {{Lang|ja-latn|shirako}} (cod milt) gunkanmaki

File:Smelt milt.jpg|Smelt milt

File:Alaska pollack liver roe milt.jpg|Alaska pollock's liver, roe, and milt

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.{{Cite journal |last=Takahashi |first=Yokio |date=9 December 2014 |title=Recovery and Separation of Rare Earth Elements Using Salmon Milt |journal=Plos One}} Because of this, it has been proposed as an environmentally-friendly way to recover rare earth elements from waste.

{{Commons category|Milt}}

• List of delicacies

{{Reflist}}

• [https://slate.com/life/2025/04/eggs-fish-dinner-sperm-eat-milt.html Bad Seed], an editorial on milt consumption from Slate

{{Diversity of fish}}

Category:Reproduction in animals

Category:Fish products

Category:Semen

Category:Fish reproduction