Fish Do Not Have Seminal Vesicles 储精囊, but Testes Only (Mostly)

choi

(1) On Jan 30, 2021 I published a posting titled "Seminal Vesicles of Fish as Japanese Food." Last night, I wondered whether fish have seminal vesicle at all. I conduct a research and find they do not. I am speaking about the fish we are familiar with. Some odd fish species do have.

(2) I am a biologist by training -- trained on humans and mice. Mammals have seminal vesicles. The Wiki page is about human's -- more specifically men's (no dog's, for example).
https://en.wikipedia.org/wiki/Seminal_vesicles
("The [pair of vesicles are 5-10cm in size, 3-5cm in diameter [I did not know they were so big], and are located between the bladder and the rectum [and above prostate] * * * The vesicles are present in many groups of mammals, but not marsupials, monotremes or carnivores. * * * [wall of] seminal vesicles contain smooth muscle * * * About 70-85% of the seminal fluid in humans originates from the seminal vesicles. The fluid consists of nutrients including fructose * * * Nutrients help support sperm until fertilisation occurs")
(a) monotreme
https://en.wikipedia.org/wiki/Monotreme
("Like reptiles, monotremes have a single cloaca. Marsupials have a separate genital tract, whereas most placental mammalian females have separate openings for reproduction (the vagina), urination (the urethra), and defecation (the anus). In monotremes [as in reptiles], only semen passes through the penis [while penetrating a female's cloaca (vagina absent)] while urine is excreted through the male's cloaca")

In monotremes, fertilized eggs in the shell exit the body via a cloaca.  (Parenthetically, duck, goose and ostriches have penis. Most other birds -- including chicken, quail, hawk and bald eagle -- do not; during copulation, opposite sexes of these birds rub cloacae -- cloaca is Latin, from Ancient Greek.)

Monotremes do have penis, separate from cloaca (for urine and feces). See Mireia Querol Rovira, Animal Genitalia: Amphibians, Reptiles and Mammals.. All You Need Is Biology, June 25, 2017
https://allyouneedisbiology.wordpress.com/tag/monotreme/
(a photo whose caption is "Echidna penis")
(b) Chan TW and Wong YC, Induction of seminal vesicle morphogenesis from dog epididymal epithelium. Anatomy and Embryology (Berlin) 194: 391 (1996)
https://pubmed.ncbi.nlm.nih.gov/8896703/  
("A number of carnivores, including the dog, do not have seminal vesicles")
(c) McKay AC, OdelugaN, Jiang J and Sharma S, Anatomy, Abdomen and Pelvis, Seminal Vesicle. StatPearls Publishing LLC, last update July 27, 2020
https://www.ncbi.nlm.nih.gov/books/NBK499854/
("The seminal vesicles are secretomotor organs composed of both secretory glandular tissue under parasympathetic control and smooth muscle under both sympathetic and parasympathetic influence. The emission phase of ejaculation, mediated through sympathetic fibers from the hypogastric nerves, leads to contractions of the seminal vesicles along with the prostate resulting in the expulsion of spermatozoa and seminal fluid into the posterior urethra")

(3)
(a) Most fish we know of are teleosts. See teleost
https://en.wikipedia.org/wiki/Teleost
("is by far the largest infraclass in the class Actinopterygii [click for the meaning of this word], the ray-finned fishes, containing 96% of all extant species of fish * * * The difference between teleosts and other bony fish lies mainly in their jaw bones; teleosts have a movable premaxilla and corresponding modifications in the jaw musculature which make it possible for them to protrude their jaws outwards from the mouth. This is of great advantage, enabling them to grab prey and draw it into the mouth.")

What does the quotation say?
• one picture is worth a thousand words, not to mention a video. See Nina Finley, Glasseye Premaxilla Protrusion. Youtube.com, Apr 7, 2014 (11 seconds).
https://www.youtube.com/watch?v=bZdVxuq4onk
• Staab KL, Holzman R, Hernandez LP, Wainwright PC, Independently evolved upper jaw protrusion mechanisms show convergent hydrodynamic function in teleost fishes. Journal of Experimental Biology, 215: 1456 (2012)
https://jeb.biologists.org/content/215/9/1456

Summary: "A protrusible upper jaw has independently evolved multiple times within teleosts * * * "

paragraph 1 of Introduction: "Predator–prey interactions in an aquatic environment are subject to the physical constraints of life in a fluid. Given that water is 900 times denser and 80 times more viscous than air, the forward motion of an aquatic predator can exert a hydrodynamic force on the prey in the same direction and push the prey away from the predator. The majority of aquatic vertebrates exploit this physical reality by suction feeding, during which they expand the volume of the buccal cavity, thus decreasing intra-oral pressure and creating a flow of water into the mouth. During prey acquisition strikes [note the word strike, in contrast to suctioning], many fishes move the mouth opening closer to the prey via a structural decoupling of the jaws from the neurocranium, known as premaxillary protrusion or jaw protrusion." (citations omitted)

(b) Salmon is teleost.
Salmon Dissection. Department of Fish and Fame, Alaska (ADFG), undated
https://www.adfg.alaska.gov/stat ... issection_guide.pdf   
("The female reproductive organ, ovaries produce eggs, * * * The male reproductive organ, testis [which is singular; plural: testes] produce [milky-white] milt [whose etymology has nothing to do with milk] which contains salmon sperm")

If you search this Web page with "milt sac," you will see a photo that shows how big it is while in reproductive season. (But there are two milt sacs, or testes, per salmon. See next.)
(c) Jennifer Luke, Akimi KIng and Susan Honea, Salmonid Anatomy & Dissection Handbook. Klamath Basin Research & Extension Center, Oregon State University and Fish and Wildlife Service (FWS), United States Department of Interior, undated
https://www.fws.gov/klamathfallsfwo/outreach/docs/SALHandbook.pdf

At page 16: two captions, one of which reads, "If the fish is female there are two sacs of eggs each held with a membrane," and the other: "If the fish is male there are two sacs or testes that produce milt when ready to spawn."
(d) I research extensively: In fish, ordinary people may call testes sperm or milt sacs, but these are not seminal vesicles. The fish testes produce and store sperm, until needed for release (they do not have penis). Whale and dolphin have penis, too, but they are not fish.

Fish produces sperm or egg once a year. In other times, the reproductive organ is there, but without gammets.