Editing Seahorse

{{Short description|Genus of bony fishes}}
{{About|the genus of fish|the creature in mythology|Hippocampus (mythology)|the structure of the brain|Hippocampus|other uses}}
{{Use dmy dates|date=June 2014}}
{{Automatic taxobox
| image = Hippocampus hippocampus (on Ascophyllum nodosum).jpg
| fossil_range = [[Lower Miocene|Lower&nbsp;Miocene]] to present – {{fossilrange|23|0}}
| image_caption = [[Short-snouted seahorse]] (''Hippocampus hippocampus'')
| name = Seahorses
| taxon = Hippocampus
| authority = [[Constantine Samuel Rafinesque|Rafinesque]], 1810<ref>{{cite book |last1=Rafinesque Schmaltz |first1=C. S.|title=Caratteri di alcuni nuovi generi e nuove specie di animali e piante della Sicilia: con varie osservazioni sopra i medesimi |date=1810 |publisher=Sanfilippo |location=Palermo |page=18 |chapter-url=https://www.biodiversitylibrary.org/page/47825945 |chapter=G. Hippocampus}}</ref><ref>[http://www.marinespecies.org/aphia.php?p=taxdetails&id=126224 ''Hippocampus'' Rafinesque, 1810], [[World Register of Marine Species|WoRMS]]</ref>
| type_species = ''[[Hippocampus hippocampus|Syngnathus hippocampus]]''
| type_species_authority = [[Linnaeus]], 1758
| subdivision_ranks = [[Species]]
| subdivision = see [[#Species|Species]].
| synonyms = *''Acentronura'' <small>[[Johann Jakob Kaup|Kaup]], 1853</small>
*''Farlapiscis'' <small>[[Gilbert Percy Whitley|Whitley]], 1931<ref>{{cite journal |last1=Whitley |first1=Gilbert P. |title=New Names for Australian Fishes |journal=The Australian Zoologist |date=1931 |volume=6 |issue=4 |page=313 |url=https://www.biodiversitylibrary.org/page/38710890}}</ref></small>
*''Jamsus'' <small>[[Isaac Ginsburg|Ginsburg]], 1937</small>
*''Macleayina'' <small>[[Henry Weed Fowler|Fowler]], 1907</small>
*''Phyllopteryx'' <small>[[William Swainson|Swainson]] 1839</small>
}}
A '''seahorse''' (also written ''sea-horse'' and ''sea horse'') is any of 46 species of small marine [[Osteichthyes|bony fish]] in the [[genus]] '''''Hippocampus'''''. The genus name comes from the [[Ancient Greek]] {{transliteration|grc|hippókampos}} ({{lang|grc|ἱππόκαμπος}}), itself from {{transliteration|grc|híppos}} ({{lang|grc|ἵππος}}) meaning "horse" and {{transliteration|grc|kámpos}} ({{lang|grc|κάμπος}}) meaning "sea monster"<ref name="SOED">{{cite book |title=Shorter Oxford English Dictionary |date=2007 |location=Oxford, UK |isbn=978-0199206872 |publisher=Oxford University Press}}</ref><ref>{{LSJ|i(ppo/kampos|ἱππόκαμπος}}, {{LSJ|i(/ppos|ἵππος}}, {{LSJ|ka/mpos|κάμπος|ref}}.</ref> or "sea animal".<ref>{{Cite book |last=Jarvis |first=Dr Peter |url=https://books.google.com/books?id=RHbnDwAAQBAJ&dq=guttulatus+latin&pg=PT1751 |title=The Pelagic Dictionary of Natural History of the British Isles: Descriptions of all Species with a Common Name |date=2020-01-13 |publisher=Pelagic Publishing Ltd |isbn=978-1-78427-196-1 |language=en}}</ref> Having a head and neck suggestive of a [[horse]], seahorses also feature segmented bony armour, an upright posture and a curled [[prehensile tail]].<ref>{{cite dictionary |url=http://www.dictionary.com/browse/sea-horse |title=sea horse or seahorse |dictionary=dictionary.com |access-date=2016-06-19}}</ref> Along with the [[pipefishes]] and seadragons (''[[Phycodurus]]'' and ''[[Phyllopteryx]]'') they form the family [[Syngnathidae]].

{{Toclimit}}

==Habitat==
Seahorses are mainly found in shallow tropical and temperate salt water throughout the world, from about 45°S to 45°N.<ref>{{Cite web |title=Home |url=http://seahorse.fisheries.ubc.ca |website=Project Seahorse |access-date=2015-11-15}}</ref> They live in sheltered areas such as [[seagrass]] beds, [[estuaries]], [[coral reef]]s, and [[mangroves]]. Four species are found in Pacific waters from [[North America]] to [[South America]]. In the Atlantic, ''[[Hippocampus erectus]]'' ranges from [[Nova Scotia]] to [[Uruguay]]. ''[[Hippocampus zosterae|H.&nbsp;zosterae]]'', known as the dwarf seahorse, is found in the [[Bahamas]].

Colonies have been found in European waters such as the [[Thames Estuary]].<ref>{{cite news |url=http://news.bbc.co.uk/1/hi/england/london/7333980.stm |title=Rare seahorses breeding in Thames |work=BBC News |date=7 April 2008 |access-date=11 November 2009}}</ref>

Two species live in the [[Mediterranean Sea]]: ''[[Hippocampus guttulatus|H.&nbsp;guttulatus]]'' (the long-snouted seahorse), and ''[[Hippocampus hippocampus|H.&nbsp;hippocampus]]'' (the short-snouted seahorse).<ref>{{Cite web|url=https://www.iucnredlist.org/resources/pipefish#|title=The IUCN Red List of Seahorses and Pipefishes in the Mediterranean Sea|website=[[IUCN Red List]]|access-date=2024-04-15}}</ref><ref>{{Cite web|url=https://www.institut-paul-ricard.org/en/especes_aquarium/seahorse/|title=Seahorse|website=[[Paul Ricard Oceanographic Institute]]|date=13 February 2019 |access-date=2024-04-15}}</ref> These species form territories; males stay within {{convert|1|m2|sqft|-1|abbr=on}} of habitat, while females range over about one hundred times that.<ref>{{Cite web |date=September 13, 2018 |title="Hippocampus, a Peculiar Fish" |url=https://www.aquaticlifelab.eu/3-9-hippocampus-a-peculiar-fish/ |website=Aquatic Life Lab |publisher=AQUATICLIFELAB}}</ref>

==Description==
[[File:Hippocampus hystrix (Spiny seahorse).jpg|thumb|upright=0.8|Spiny seahorse ''[[Hippocampus histrix|H.&nbsp;histrix]]'' from [[East Timor]] holding on to soft coral with its prehensile tail]]
[[File:Hippocampus jayakari, Egipto.jpg|thumb|''H. jayakari'']]
Seahorses range in size from {{convert|1.5|to|35|cm|in|1|abbr=on}}.<ref>{{cite magazine |url=http://animals.nationalgeographic.com/animals/fish/sea-horse/ |title=Seahorses, Seahorse Pictures, Seahorse Facts |magazine=National Geographic |access-date=17 May 2012|archive-url=https://web.archive.org/web/20161014061634/https://www.nationalgeographic.com/animals/fish/hub/seahorses/|archive-date=14 October 2016|url-status=dead}}</ref> They are named for their [[Horse|equine]] appearance, with bent necks and long snouted heads and a distinctive trunk and tail. Although they are [[bony fish]], they do not have scales, but rather thin skin stretched over a series of bony plates, which are arranged in rings throughout their bodies. Each species has a distinct number of rings.<ref>{{Cite web |title=Observatoire Océanologique de Banyuls sur mer |url=http://www.obs-banyuls.fr/ |website=www.obs-banyuls.fr |access-date=2015-11-16}}</ref> The armor of bony plates also protects them against predators,<ref>{{cite journal |last1=Porter |first1=Michael M |last2=Novitskaya |first2=Ekaterina |last3=Castro-Ceseña |first3=Ana Bertha |last4=Meyers |first4=Marc A |last5=McKittrick |first5=Joanna |date=2013 |title=Highly deformable bones: Unusual deformation mechanisms of seahorse armor |journal=Acta Biomaterialia |volume=9 |issue=6 |pages=6763–6770 |doi=10.1016/j.actbio.2013.02.045 |pmid=23470547}}</ref> and because of this outer skeleton, they no longer have ribs.<ref>{{Cite web |url=https://www.sciencedaily.com/releases/2016/12/161214151616.htm |title=The galloping evolution in seahorses: Entire genome of the seahorse sequenced |website=ScienceDaily}}</ref> Seahorses swim upright, propelling themselves using the [[dorsal fin]], another characteristic not shared by their close [[pipefish]] relatives, which swim horizontally. [[Aeoliscus strigatus|Razorfish]] are the only other fish that swim vertically. The [[pectoral fin]]s, located on either side of the head behind their eyes, are used for steering. They lack the [[caudal fin]] typical of fishes. Their [[prehensile tail]] is composed of square-like rings that can be unlocked only in the most extreme conditions.<ref>{{cite journal |last1=Porter |first1=Michael M |last2=Adriaens |first2=Dominique |last3=Hatton |first3=Ross L |last4=Meyers |first4=Marc A |last5=McKittrick |first5=Joanna |title=Why the seahorse tail is square |journal=Science |date=2015 |volume=349 |issue=6243 |page=aaa6683 |doi=10.1126/science.aaa6683 |pmid=26138983 |doi-access=free }}</ref> They are adept at camouflage, and can grow and reabsorb spiny appendages depending on their habitat.<ref>{{Cite journal |title=Seahorse Tagging Project, Studland Bay, Dorset, UK |journal=Marine Biodiversity Records |date=2010-01-01 |issn=1755-2672 |volume=3 |doi=10.1017/S175526721000062X |first1=N. |last1=Garrick-Maidment |first2=S. |last2=Trewhella |first3=J. |last3=Hatcher |first4=K.j. |last4=Collins |first5=J.j. |last5=Mallinson|doi-broken-date=14 April 2025 |bibcode=2010MBdR....3E..73G }}</ref>

Unusual among fish, a seahorse has a flexible, well-defined neck. It also sports a crown-like spine or horn on its head, termed a "coronet", which is distinct for each species.<ref>{{Cite journal |last=Freret-Meurer |first=Natalie |title=Seahorse Fingerprints: A New Individual Identification Technique |journal=Environmental Biology of Fishes |year=2013 |volume=96 |issue=12 |pages=1399–1405 |doi=10.1007/s10641-013-0118-6 |bibcode=2013EnvBF..96.1399F |s2cid=13917616}}</ref>

Seahorses swim extremely poorly, rapidly fluttering a dorsal fin and using pectoral fins to steer. The slowest-moving fish in the world is ''[[Hippocampus zosterae|H.&nbsp;zosterae]]'' (the dwarf seahorse), with a top speed of about {{convert|5|ft|m|1|order=flip|abbr=on}} per hour.<ref>[[Guinness Book of World Records]] (2009)</ref> Since they are poor swimmers, they are most likely to be found resting with their prehensile tail wound around a stationary object. They have long snouts, which they use to suck up food, and their eyes can move independently of each other like those of a [[chameleon]].<ref>{{cite book |last1=Lourie |first1=Sara |title=Seahorses: A Life-size Guide to Every Species |publisher=Ivy Press |isbn=9781782403210 |language=en |year=2016}}</ref>

==Evolution and fossil record==
Anatomical evidence, supported by molecular, physical, and genetic evidence, demonstrates that seahorses are highly modified [[pipefish]]. The fossil record of seahorses, however, is very sparse. The best known and best studied fossils are specimens of ''[[Hippocampus guttulatus]]'' (though literature more commonly refers to them under the synonym of ''H.&nbsp;ramulosus''), from the [[Marecchia River]] formation of [[Rimini Province]], Italy, dating back to the [[Lower Pliocene]], about 3''&nbsp;''million years ago. The earliest known seahorse fossils are of two pipefish-like species, ''[[Hippocampus sarmaticus|H.&nbsp;sarmaticus]]'' and ''[[Hippocampus slovenicus|H.&nbsp;slovenicus]]'', from the [[coprolite|coprolitic]] horizon of [[Tunjice]] Hills, a [[middle Miocene]] [[lagerstätte]] in [[Slovenia]] dating back about 13''&nbsp;''million years.<ref>{{cite journal |author1=Žalohar J. |author2=Hitij T. |author3=Križnar M. |year=2009 |title=Two new species of seahorses (Syngnathidae, ''Hippocampus'') from the Middle Miocene (Sarmatian) Coprolitic Horizon in Tunjice Hills, Slovenia: The oldest fossil record of seahorses |journal=Annales de Paléontologie |volume=95 |issue=2 |pages=71–96 |doi=10.1016/j.annpal.2009.03.002|bibcode=2009AnPal..95...71Z }}</ref>

[[Molecular clock|Molecular dating]] implies that pipefish and seahorses diverged during the Late [[Oligocene]]. This has led to speculation that seahorses evolved in response to large areas of shallow water, newly created as the result of [[tectonic]] events. The shallow water would have allowed the expansion of seagrass habitats that served as [[camouflage]] for the seahorses' upright posture.<ref name=Teske-2009>{{cite journal |author1=Teske PR |author2=Beheregaray LB |title=Evolution of seahorses' upright posture was linked to Oligocene expansion of seagrass habitats |journal=Biol. Lett. |volume=5 |issue=4 |pages=521–3 |year=2009 |doi=10.1098/rsbl.2009.0152 |pmc=2781918 |pmid=19451164}}</ref> These tectonic changes occurred in the western [[Pacific Ocean]], pointing to an origin there, with molecular data suggesting two later, separate invasions of the [[Atlantic Ocean]].<ref name=Teske-2004>{{cite journal |doi=10.1016/S1055-7903(03)00214-8 |author1=Teske PR |author2=Cherry MI |author3=Matthee CA |title=The evolutionary history of seahorses (Syngnathidae: Hippocampus): molecular data suggest a West Pacific origin and two invasions of the Atlantic Ocean |journal=Mol Phylogenet Evol |volume=30 |issue=2 |pages=273–86 |year=2004 |pmid=14715220 |bibcode=2004MolPE..30..273T }}</ref> In 2016, a study published in ''Nature'' found the seahorse genome to be the most rapidly evolving fish genome studied so far.<ref name=nature20595>{{cite journal |title=The seahorse genome and the evolution of its specialized morphology |journal=Nature |date=14 December 2016 |volume=540 |issue=7633 |doi=10.1038/nature20595 |pmid=27974754 |bibcode=2016Natur.540..395L |pages=395–399 |last1=Lin |first1=Qiang |last2=Fan |first2=Shaohua |last3=Zhang |first3=Yanhong |last4=Xu |first4=Meng |last5=Zhang |first5=Huixian |last6=Yang |first6=Yulan |last7=Lee |first7=Alison P |last8=Woltering |first8=Joost M |last9=Ravi |first9=Vydianathan |last10=Gunter |first10=Helen M |last11=Luo |first11=Wei |last12=Gao |first12=Zexia |last13=Lim |first13=Zhi Wei |last14=Qin |first14=Geng |last15=Schneider |first15=Ralf F |last16=Wang |first16=Xin |last17=Xiong |first17=Peiwen |last18=Li |first18=Gang |last19=Wang |first19=Kai |last20=Min |first20=Jiumeng |last21=Zhang |first21=Chi |last22=Qiu |first22=Ying |last23=Bai |first23=Jie |last24=He |first24=Weiming |last25=Bian |first25=Chao |last26=Zhang |first26=Xinhui |last27=Shan |first27=Dai |last28=Qu |first28=Hongyue |last29=Sun |first29=Ying |last30=Gao |first30=Qiang |last31=Huang |first31=Liangmin |last32=Shi |first32=Qiong |last33=Meyer |first33=Axel |last34=Venkatesh |first34=Byrappa |pmc=8127814 |display-authors=6 |doi-access=free }}</ref>

The evolution of seahorses from pipefish may have been an adaptation related to the biomechanics of prey capture. The unique posture of the seahorse allows them to capture small shrimps at larger distances than the pipefish is capable of.<ref>{{Cite journal |last1=Van Wassenbergh |first1=Sam |last2=Roos |first2=Gert |last3=Ferry |first3=Lara |date=2011-01-25 |title=An adaptive explanation for the horse-like shape of seahorses |journal=Nature Communications |volume=2 |issue=1 |pages=164 |doi=10.1038/ncomms1168 |pmid=21266964 |bibcode=2011NatCo...2..164V |issn=2041-1723 |doi-access=free}}</ref>

==Reproduction==
{{see also|Animal sexual behavior#Seahorse}}
[[File:Seahorse lifecycle.svg|thumbnail|Seahorse life-cycle]]
The male seahorse is equipped with a brood pouch on the ventral, or front-facing, side of the tail. When mating, the female seahorse deposits up to 1,500 eggs in the male's pouch. The male carries the [[egg (biology)#Fish and amphibian eggs|egg]]s for 9 to 45 days until the seahorses emerge fully developed, but very small. The young are then released into the water, and the male often mates again within hours or days during the breeding season.<ref>{{cite journal |author1=Foster S.J |author2=Vincent C.J. |title=Life history and ecology of seahorses: implications for conservation and management |journal=Journal of Fish Biology |volume=65 |pages=1–61 |year=2004 |issue=1 |doi=10.1111/j.0022-1112.2004.00429.x|doi-access=free |bibcode=2004JFBio..65....1F }}</ref>

===Courtship===
Before breeding, seahorses may court for several days. Scientists believe the [[Courtship display|courtship]] behavior synchronizes the animals' movements and reproductive states, so that the male can receive the eggs when the female is ready to deposit them. During this time, they may change color, swim side by side holding tails or grip the same strand of sea grass with their tails, and wheel around in unison in what is known as a "predawn dance". They eventually engage in a "true courtship dance" lasting about 8 hours, during which the male pumps water through the egg pouch on his trunk which expands and opens to display its emptiness. When the female's eggs reach maturity, she and her mate let go of any anchors and drift upward snout-to-snout, out of the sea grass, often spiraling as they rise. They interact for about 6 minutes, reminiscent of courtship.<ref name="autogenerated2" /> The female inserts her [[ovipositor]] into the male's brood pouch and deposits dozens to thousands of eggs. As the female releases her eggs, her body slims while his swells. Both animals then sink back into the sea grass and she swims away.<ref name="autogenerated2" />

==== Phases of courtship ====
Seahorses exhibit four phases of courtship that are indicated by clear behavioral changes and changes in the intensity of the courtship act. Phase 1, the initial courtship phase, typically takes place in the early morning one or two days before physical [[copulation (zoology)|copulation]]. During this phase the potential mates brighten in colour, quiver, and display rapid side-to-side body vibrations. These displays are performed alternately by both the male and the female seahorse. The following phases, 2 through 4, happen sequentially on the day of copulation. Phase 2 is marked by the female pointing, a behaviour in which the female will raise her head to form an oblique angle with her body. In phase 3 males will also begin the same pointing behaviour in response to the female. Finally, the male and female will repeatedly rise upward together in a [[water column]] and end in mid-water copulation, in which the female will transfer her eggs directly into the male's brood pouch.<ref name="Masonjones-1996">{{Cite journal |last1=Masonjones |first1=Heather D. |last2=Lewis |first2=Sara M. |date=1996 |title=Courtship Behavior in the Dwarf Seahorse, ''Hippocampus zosterae'' |journal=Copeia |volume=1996 |issue=3 |pages=634–640 |doi=10.2307/1447527 |jstor=1447527}}</ref>

===== Phase 1: Initial courtship =====
This initial courtship behaviour takes place about 30 minutes after dawn on each courtship day, until the day of copulation. During this phase the males and females will remain apart during the night, but after dawn they will come together in a side-by-side position, brighten, and engage in courtship behaviour for about 2 to 38 minutes. There is repeated reciprocal quivering. This starts when the male approaches the female, brightens and begins to quiver. The female will follow the male with her own display, in which she will also brighten and quiver about 5 seconds later. As the male quivers, he will rotate his body towards the female who will then rotate her body away. During phase 1 the tails of both seahorses are positioned within 1&nbsp;cm of each other on the same [[Holdfast (biology)|hold-fast]] and both of their bodies are angled slightly outward from the point of attachment. However, the female will shift her tail attachment site, causing the pair to circle their common hold-fast.<ref name="Masonjones-1996" />

===== Phase 2: Pointing and pumping =====
This phase begins with the female beginning her pointing posture, by leaning her body towards the male, who will simultaneously lean away and quiver. This phase can last up to 54 minutes. Following phase 2 is a latency period (typically between 30 minutes and four hours), during which the seahorses display no courtship behaviour and females are not bright; males will usually display a pumping motion with their body.<ref name="Masonjones-1996" />

===== Phase 3: Pointing – pointing =====
[[File:Seahorse mating dance.JPG|thumb|Seahorses in Phase 2 of courtship]]
The third phase begins with the females brightening and assuming the pointing position. The males respond with their own brightening and pointing display. This phase ends with the male departing. It usually lasts nine minutes and can occur one to six times during courtship.<ref name="Masonjones-1996" />

===== Phase 4: Rising and copulation =====
The final courtship phase includes 5–8 bouts of courtship. Each bout of courtship begins with both the male and female anchored to the same plant about 3&nbsp;cm apart; usually they are facing each other and are still bright in colour from the previous phase. During the first bout, following the facing behaviour, the seahorses will rise upward together anywhere from 2 to 13&nbsp;cm in a water column. During the final rise, the female will insert her [[ovipositor]] and transfer her eggs through an opening into the male's brood pouch.<ref name="Masonjones-1996" />

=== Fertilization ===
During fertilization in ''Hippocampus kuda'', the brood pouch was found to be open for only six seconds while egg deposition occurred. During this time seawater entered the pouch where the spermatozoa and eggs meet in a seawater milieu. This hyperosmotic environment facilitates sperm activation and motility. The fertilization is therefore regarded as being physiologically 'external' within a physically 'internal' environment after the closure of the pouch.<ref>{{Cite journal |title=Dimorphic sperm and the unlikely route to fertilisation in the yellow seahorse |journal=Journal of Experimental Biology |date=2007-02-01 |issn=0022-0949 |pmid=17234612 |pages=432–437 |volume=210 |issue=3 |doi=10.1242/jeb.02673 |first1=Katrien J. W. Van |last1=Look |first2=Borys |last2=Dzyuba |first3=Alex |last3=Cliffe |first4=Heather J. |last4=Koldewey |first5=William V. |last5=Holt |doi-access=free}}</ref> It is believed that this protected form of fertilization reduces [[sperm competition]] among males. Within the Syngnathidae (pipefishes and seahorses) protected fertilization has not been documented in the pipefishes but the lack of any distinct differences in the relation of testes size to body size suggests that pipefishes may also have evolved mechanisms for more efficient fertilization with reduced sperm competition.<ref>{{cite journal |journal=Biological Journal of the Linnean Society |year=2004 |volume=83 |issue=3 |pages=369–376 |title=Testes investment and spawning mode in pipefishes and seahorses (Syngnathidae) |author1=Kvarnemo, Charlotta |author2=Simmons, Leigh W. |doi=10.1111/j.1095-8312.2004.00395.x |doi-access=free}}</ref>

===Gestation===
[[File:Hippocampus haema mating.jpg|thumb|Seahorses in Phase 4 of courtship]]
The fertilized eggs are then embedded in the pouch wall and become surrounded by a spongy tissue.<ref name="Project Seahorse">{{cite web |title=The biology of seahorses: Reproduction |publisher=The Seahorse Project |url=http://seahorse.fisheries.ubc.ca/biology5.html |access-date=8 May 2007 |archive-url=https://web.archive.org/web/20090303051206/http://seahorse.fisheries.ubc.ca/biology5.html |archive-date=3 March 2009}}</ref> The pouch provides oxygen,<ref>{{cite journal |last1=Dudley |first1=Jessica |title=Structural changes to the brood pouch of male pregnant seahorses (Hippocampus abdominalis) facilitate exchange between father and embryos |journal=Placenta |date=October 2021 |volume=114 |pages=115–123 |doi=10.1016/j.placenta.2021.09.002 |pmid=34517263 |s2cid=237505281 |hdl=2123/31726 |hdl-access=free }}</ref> as well as a controlled environment incubator. Though the egg yolk contributes nourishment to the developing embryo, the male sea horses contribute additional nutrients such as energy-rich lipids and also calcium to allow them to build their skeletal system, by secreting them into the brood pouch that are absorbed by the embryos. Further they also offer immunological protection, osmoregulation, gas exchange and waste transport.<ref>{{Cite journal |title=Seahorse Brood Pouch Transcriptome Reveals Common Genes Associated with Vertebrate Pregnancy |journal=Molecular Biology and Evolution |date=2015-09-01 |issn=0737-4038 |pmid=26330546 |pages=3114–31 |doi=10.1093/molbev/msv177 |first1=Camilla M. |last1=Whittington |first2=Oliver W. |last2=Griffith |first3=Weihong |last3=Qi |first4=Michael B. |last4=Thompson |first5=Anthony B. |last5=Wilson |volume=32 |issue=12 |doi-access=free|hdl=20.500.11850/110832 |hdl-access=free }}</ref>

The eggs then hatch in the pouch, where the salinity of the water is regulated; this prepares the newborns for life in the sea.<ref name="autogenerated2">{{Cite journal |doi=10.2307/4012130 |url=http://ase.tufts.edu/biology/labs/lewis/news/articles/2000ScienceNews.pdf |archive-url=https://web.archive.org/web/20110818082935/http://ase.tufts.edu/biology/labs/lewis/news/articles/2000ScienceNews.pdf |archive-date=2011-08-18 |url-status=deviated |jstor=4012130 |title=Pregnant: And Still Macho |journal=Science News |volume=157 |issue=11 |pages=168–170 |year=2000 |last1=Milius |first1=S.}}</ref><ref>{{Cite journal |pmid=10640362 |year=2000 |last1=Masonjones |first1=H. D. |last2=Lewis |first2=S. M. |title=Differences in potential reproductive rates of male and female seahorses related to courtship roles |journal=Animal Behaviour |volume=59 |issue=1 |pages=11–20 |doi=10.1006/anbe.1999.1269 |s2cid=5999610}}</ref><ref name="autogenerated1">{{cite web |author=Danielson, Stentor |work=National Geographic News |date=14 June 2002 |title=Seahorse Fathers Take Reins in Childbirth |url=http://news.nationalgeographic.com/news/2002/06/0614_seahorse_recov.html|archive-url=https://web.archive.org/web/20020624035320/http://news.nationalgeographic.com/news/2002/06/0614_seahorse_recov.html|url-status=dead|archive-date=24 June 2002}}</ref> 

===Birth===
The number of young released by the male seahorse averages 100–1000 for most species, but may be as low as 5 for the smaller species, or as high as 2,500.<ref name="Project Seahorse"/> When the [[fry (biology)|fry]] are ready to be born, the male expels them with muscular contractions. He typically gives birth at night and is ready for the next batch of eggs by morning when his mate returns. Like almost all other fish species, seahorses do not nurture their young after birth. Infants are susceptible to predators or ocean currents which wash them away from feeding grounds or into temperatures too extreme for their delicate bodies. Less than 0.5% of infants survive to adulthood, explaining why litters are so large. These survival rates are actually fairly high compared to other fish, because of their protected gestation, making the process worth the great cost to the father. The eggs of most other fish are abandoned immediately after fertilization.<ref name="autogenerated1" />

===Reproductive roles===
[[File:Diagram of a pregnant male seahorse.png|thumb|left| Diagram of a pregnant male seahorse (''[[Hippocampus comes]]'')<ref name=nature20595/>]]
[[File:Tehotny morsky konik.jpg|thumb|right|Pregnant male seahorse at the [[New York Aquarium]]]]

Reproduction is energetically costly to the male. This brings into question why the sexual role reversal even takes place. In an environment where one partner incurs more energy costs than the other, [[Bateman's principle]] suggests that the lesser contributor takes the role of the aggressor. Male seahorses are more aggressive and sometimes fight for female attention. According to [[Amanda Vincent]] of [[Project Seahorse]], only males tail-wrestle and snap their heads at each other. This discovery prompted further study of energy costs. To estimate the female's direct contribution, researchers chemically analyzed the energy stored in each egg. To measure the burden on the males, oxygen consumption was used. By the end of incubation, the male consumed almost 33% more oxygen than before mating. The study concluded that the female's energy expenditure while generating eggs is twice that of males during incubation, confirming the standard hypothesis.<ref name="autogenerated2" />

Why the male seahorse (and other members of the Syngnathidae) carries the offspring through gestation is unknown, though some researchers believe it allows for shorter birthing intervals, in turn resulting in more offspring.<ref>{{cite journal |title=Operational Sex Ratios in Seahorses |author=Vincent, Amanda C. J. |journal=Behaviour |volume=128 |issue=1/2 |year=1994 |pages=153–167 |jstor=4535169 |doi=10.1163/156853994X00091}}</ref> Given an unlimited number of ready and willing partners, males have the potential to produce 17% more offspring than females in a breeding season. Also, females have "time-outs" from the reproductive cycle 1.2 times longer than those of males. This seems to be based on mate choice, rather than physiology. When the female's eggs are ready, she must lay them in a few hours or eject them into the water column. Making eggs is a huge cost to her physically, since they amount to about a third of her body weight. To protect against losing a clutch, the female demands a long courtship. The daily greetings help to cement the bond between the pair.<ref>{{cite web |url=http://petseahorse.com/male-seahorses-pregnant/ |archive-url=https://archive.today/20130717075359/http://petseahorse.com/male-seahorses-pregnant/ |url-status=usurped |archive-date=17 July 2013 |title=Why Do Male Seahorses Get Pregnant? |publisher=Petseahorse.com }}</ref>

===Monogamy===
Though seahorses are not known to mate for life, many species form [[pair bond]]s that last through at least the breeding season. Some species show a higher level of mate fidelity than others.<ref>{{cite journal |author1=Kvarnemo C |author2=Moore G.I |author3=Jones A.G |author4=Nelson W.S |author5=Avise J.C. |title=Monogamous pair bonds and mate switching in the Western Australian seahorse ''Hippocampus subelongatus'' |journal=J. Evol. Biol. |volume=13 |issue=6 |pages=882–8 |year=2000 |doi=10.1046/j.1420-9101.2000.00228.x|s2cid=40777563 |url=https://escholarship.org/uc/item/2zm2d5gx }}</ref><ref>{{cite journal |doi=10.1016/0003-3472(95)80011-5 |author1=Vincent C.J. |author2=Sadler L.M. |title=Faithful pair bonds in wild seahorses, ''Hippocampus whitei'' |journal=Anim. Behav. |volume=50 |pages=1557–1569 |year=1995 |url=http://courses.umass.edu/wfcon470/Vincent%20and%20Sadler%2095.pdf |archive-url=https://web.archive.org/web/20110723140601/http://courses.umass.edu/wfcon470/Vincent%20and%20Sadler%2095.pdf |archive-date=23 July 2011 |issue=6 |s2cid=53192875 }}</ref> However, many species readily switch mates when the opportunity arises. ''H.&nbsp;abdominalis'' and ''H.&nbsp;breviceps'' have been shown to breed in groups, showing no continuous mate preference. Many more species' mating habits have not been studied, so it is unknown how many species are actually monogamous, or how long those bonds actually last.<ref>{{cite web |url=http://www.fusedjaw.com/biology/seahorse-monogamy/ |title=What's Love Got to Do With It? The Truth About Seahorse Monogamy |publisher=fusedjaw.com |author=Weiss, Tami |date=10 April 2010}}</ref>

Although [[Monogamy in animals|monogamy]] within fish is not common, it does appear to exist for some. In this case, the [[mate guarding|mate-guarding]] hypothesis may be an explanation. This hypothesis states, "males remain with a single female because of ecological factors that make male parental care and protection of offspring especially advantageous."<ref>{{cite book |author=Alcock, John |author-link=John Alcock (behavioral ecologist) |title=Animal Behavior |publisher=Sinauer |location=Massachusetts |year=2005 |isbn=978-0878930050 |pages=370–1 |edition=8th }}</ref> Because the rates of survival for newborn seahorses are so low, incubation is essential. Though not proven, males could have taken on this role because of the lengthy period the females require to produce their eggs. If males incubate while females prepare the next clutch (amounting to a third of body weight), they can reduce the interval between clutches.{{citation needed|date=July 2015}}

==Feeding habits==
[[File:Black Sea fauna Seahorse.JPG|thumb|right|Seahorses rely on stealth to ambush small prey such as [[copepod]]s. They use [[Aquatic predation#Pivot feeding|pivot feeding]] to catch the copepod, which involves rotating their snout at high speed and then sucking in the copepod.<ref name="Langley2013" />]]Seahorses use their long snouts to eat their food with ease. However, they are slow to consume their food and have extremely simple digestive systems that lack a stomach, so they must eat constantly to stay alive.<ref name="Woods2002">{{Cite journal|last=Woods|first=Chris M. C.|date=September 2002|title=Natural diet of the seahorse ''Hippocampus abdominalis''|journal=New Zealand Journal of Marine and Freshwater Research|volume=36|issue=3|pages=655–660|doi=10.1080/00288330.2002.9517121|issn=0028-8330|doi-access=free|bibcode=2002NZJMF..36..655W }}</ref> Seahorses are not very good swimmers, and for this reason they need to anchor themselves to [[seaweed]], [[coral]] or anything else that will keep the seahorse in place. They do this by using their [[prehensile tail]]s to grasp their object of choice.<ref>{{Cite journal|last1=Flynn|first1=A. J.|last2=Ritz|first2=D. A.|date=June 1999|title=Effect of habitat complexity and predatory style on the capture success of fish feeding on aggregated prey|journal=Journal of the Marine Biological Association of the United Kingdom|volume=79|issue=3|pages=487–494|issn=1469-7769|doi=10.1017/s0025315498000617|bibcode=1999JMBUK..79..487F |s2cid=86160386 }}</ref> Seahorses feed on small [[crustaceans]] floating in the water or crawling on the bottom. With excellent [[camouflage]], seahorses ambush prey that floats within striking range, sitting and waiting until an optimal moment.<ref name="Woods2002"/> [[Mysid shrimp]] and other small crustaceans are favorites, but some seahorses have been observed eating other kinds of [[invertebrates]] and even [[larval]] fish. In a study of seahorses, the distinctive head morphology was found to give them a hydrodynamic advantage that creates minimal interference while approaching an evasive prey. Thus the seahorse can get very close to the [[copepod]]s on which it preys.<ref name="Langley2013">{{cite web |author=Langley, Liz |date=26 November 2013 |url=http://newswatch.nationalgeographic.com/2013/11/26/why-does-the-seahorse-have-its-odd-head-mystery-solved/ |archive-url=https://web.archive.org/web/20131127023754/http://newswatch.nationalgeographic.com/2013/11/26/why-does-the-seahorse-have-its-odd-head-mystery-solved/ |url-status=dead |archive-date=27 November 2013 |title=Why Does the Seahorse Have Its Odd Head? Mystery Solved – News Watch |publisher=Newswatch.nationalgeographic.com }}</ref><ref name="Gemmell-2013">{{Cite journal |doi=10.1038/ncomms3840 |title=Morphology of seahorse head hydrodynamically aids in capture of evasive prey |journal=Nature Communications |volume=4 |year=2013 |last1=Gemmell |first1=B. J. |last2=Sheng |first2=J. |last3=Buskey |first3=E. J. |pmid=24281430 |bibcode=2013NatCo...4.2840G |page=2840 |doi-access=free}}</ref> After successfully closing in on the prey without alerting it, the seahorse gives an upward thrust and rapidly rotates the head aided by large tendons that store and release elastic energy, to bring its long snout close to the prey. This step is crucial for prey capture, as oral suction only works at a close range. This two-phase prey capture mechanism is termed pivot-feeding.<ref name="Gemmell-2013" /><ref>{{Cite journal |title=Extremely fast prey capture in pipefish is powered by elastic recoil |journal=Journal of the Royal Society Interface |date=2008-03-06 |issn=1742-5689 |pmc=2607401 |pmid=17626004 |pages=285–296 |volume=5 |issue=20 |doi=10.1098/rsif.2007.1124 |first1=Sam Van |last1=Wassenbergh |first2=James A. |last2=Strother |first3=Brooke E. |last3=Flammang |first4=Lara A. |last4=Ferry-Graham |first5=Peter |last5=Aerts}}</ref> Seahorses have three distinctive feeding phases: preparatory, expansive, and recovery. During the preparatory phase, the seahorse slowly approaches the prey while in an upright position, after which it slowly flexes its head ventrally. In the expansive phase, the seahorse captures its prey by simultaneously elevating its head, expanding the buccal cavity, and sucking in the prey item. During the recovery phase, the jaws, head, and hyoid apparatus of the seahorse return to their original positions.<ref>{{Cite journal|last1=Bergert|first1=B. A.|last2=Wainwright|first2=P. C.|date=1997-03-14|title=Morphology and kinematics of prey capture in the syngnathid fishes ''Hippocampus erectus'' and ''Syngnathus floridae''|journal=Marine Biology|volume=127|issue=4|pages=563–570|doi=10.1007/s002270050046|bibcode=1997MarBi.127..563B |s2cid=84452341|issn=0025-3162}}</ref>

The amount of available cover influences the seahorse's feeding behaviour. For example, in wild areas with small amounts of vegetation, seahorses will sit and wait, but an environment with extensive vegetation will prompt the seahorse to inspect its environment, feeding while swimming rather than sitting and waiting. Conversely, in an aquarium setting with little vegetation, the seahorse will fully inspect its environment and makes no attempt to sit and wait.<ref>{{Cite journal|last1=Rosa|first1=Ierecê L.|last2=Dias|first2=Thelma L.|last3=Baum|first3=Julia K.|date=2002|title=Threatened Fishes of the World: ''Hippocampus reidi'' Ginsburg, 1933 (Syngnathidae)|journal=Environmental Biology of Fishes|volume=64|issue=4|pages=378|doi=10.1023/a:1016152528847|bibcode=2002EnvBF..64..378R |s2cid=26782777|issn=0378-1909}}</ref>
[[File:Pygmy Seahorse - Hippocampus bargibanti.jpg|alt=|thumb|Seahorse hiding using camouflage]]
[[Image:Seahorse-aquarium.jpg|thumb|Seahorses (''[[Hippocampus erectus]]'') at the [[New England Aquarium]]|alt=]]

==Threats of extinction==
Because data is lacking on the sizes of the various seahorse populations, as well as other issues including how many seahorses are dying each year, how many are being born, and the number used for souvenirs, there is insufficient information to assess their risk of extinction, and the risk of losing more seahorses remains a concern. Coral reefs and seagrass beds are deteriorating mainly due to human activity impacts (e.g., fishing using illegal methods), reducing viable habitats for seahorses.<ref name=":0" /><ref>Lourie, Sarah A.; Foster, Sarah J.; Cooper, Ernest W.T. and Vincent, Amanda C.J. (2004) [http://www.traffic.org/species-reports/traffic_species_fish29.pdf ''A Guide to the Identification of Seahorses'']. Project Seahorse Advancing Marine Conservation, {{ISBN|0-89164-169-6}}.</ref> Additionally, [[bycatch]] in many areas causes high cumulative effects on seahorses, with an estimated 37 million individuals being removed annually over 21 countries.<ref>{{cite journal |last1=Lawson |first1=J. M. |last2=Foster |first2=S. J. |last3=Vincent |first3=A. C. J. |date=January 2017 |title=Low bycatch rates add up to big numbers for a genus of small fishes |journal=Fisheries Magazine |volume=42 |issue=1 |pages=19–33 |publisher=American Fisheries Society |doi=10.1080/03632415.2017.1259944|bibcode=2017Fish...42...19L }}</ref>

==Aquaria==
{{more citations needed|section|date=January 2018}}While many [[aquarium]] [[hobbyists]] keep them as pets, seahorses collected from the wild tend to fare poorly in home aquaria. Many eat only live foods such as [[brine shrimp]] and are prone to stress, which damages their [[immune system]]s and makes them susceptible to disease.<ref>{{Cite web |title=Seahorse Stress, Disease & Health Problems {{!}} Ocean Rider Kona |url=https://seahorse.com/seahorse-stress-disease-health-problems/ |access-date=2024-04-08 |website=Seahorse.com |language=en-US}}</ref>

In recent years, however, [[captive breeding]] has become more popular. Such seahorses survive better in captivity, and are less likely to carry diseases. They eat frozen [[mysidacea]] ([[crustaceans]]) that are readily available from aquarium stores,<ref name="fusedjaw.com">{{cite web|url=http://www.fusedjaw.com/food-and-nutrition/seahorse-foods-and-feeding/ |title=Seahorse and Pipefish Foods &#124; Tami Weiss |publisher=Fusedjaw.com |date=25 June 2005 |access-date=11 November 2009}}</ref> and do not experience the stress of moving out of the wild. Although captive-bred seahorses are more expensive, they take no toll on wild populations.

Seahorses should be kept in an aquarium with low flow and placid tank mates. They are slow feeders, so fast, aggressive feeders will leave them without food.<ref name="fusedjaw.com"/> Seahorses can coexist with many species of shrimp and other [[bottom feeder|bottom-feeding]] creatures. [[goby|Gobies]] also make good tank-mates. Keepers are generally advised to avoid [[eel]]s, [[tang (fish)|tangs]], [[triggerfish]], [[squid]], [[octopus]], and [[sea anemone]]s.<ref>{{cite web|url=http://www.fusedjaw.com/aquariumcare/seahorse-tankmates-whats-safe-whats-not/ |title=Seahorse Tankmates &#124; Will Wooten |publisher=Fusedjaw.com |date=25 June 2004 |access-date=11 November 2009}}</ref>

Water quality is very important for the survival of seahorses in an aquarium. They are delicate species which should not be added to a new tank. The water parameters are recommended to be as follows although these fish may acclimatise to different water over time: 
*Temperature: {{convert|23|–|28|C|F}} 
*pH: 8.1–8.4 
*Ammonia: 0&nbsp;mg/L (0&nbsp;ppm) (0.01&nbsp;mg/L (0.01&nbsp;ppm) may be tolerated for short periods) 
*Nitrite: 0&nbsp;mg/L (0&nbsp;ppm) (0.125&nbsp;mg/L (0.125&nbsp;ppm) may be tolerated for short periods) 
*S.G.: 1.021–1.024 at {{convert|23|–|24|C|F}}{{citation needed|date=July 2015}}
A water-quality problem will affect fish behaviour and can be shown by clamped fins, reduced feeding, erratic swimming, and gasping at the surface.<ref>[http://www.seahorseaquariums.ie/info/27%20How%20to%20care%20for%20Seahorses%20&%20Pipefish.pdf How to care for Seahorses & Pipefish]. seahorseaquariums.ie</ref> Seahorses require vertical swimming space to perform reproductive functions and to prevent depth-related health conditions like gas bubble disease, so a [[Refugium (fishkeeping)|refugium]] that is at least 20 inches by 51 centimeters deep is recommended inside an aquarium.<ref name="y218">{{cite web |last=Giwojna |first=Pete | title=Choosing Seahorse Species for the Reef | website=Tropical Fish Hobbyist Magazine | url=https://www.tfhmagazine.com/articles/saltwater/a-seahorse-reef-part-two-choosing-your-seahorses-full-article | access-date=May 28, 2024}}</ref>

Animals sold as "[[freshwater]] seahorses" are usually the closely related [[pipefish]], of which a few species live in the lower reaches of rivers. The supposed true "freshwater seahorse" called ''[[Hippocampus aimei|H.&nbsp;aimei]]'' is not a valid species, but a [[Synonym (taxonomy)|synonym]] sometimes used for [[Barbour's seahorse|Barbour's]] and [[hedgehog seahorse]]s. The latter, which is often confused with the former, can be found in [[estuarine]] environments, but is not actually a freshwater fish.<ref>{{cite web|url=http://fishbase.org/Summary/speciesSummary.php?ID=25974&genusname=Hippocampus&speciesname=spinosissimus |title=Hippocampus spinosissimus |publisher=Fishbase |access-date=11 November 2009}}</ref>

==Consumption==
[[File:Seahorse Skeleton Macro 8 - edit.jpg|thumb|upright|left|Dried seahorse]]

[[File:Seahorses scorpions skewer.jpg|thumb|Seahorse and [[scorpion]] skewers as [[street food]]]]
Seahorse populations are thought to be [[endangered species|endangered]] as a result of [[overfishing]] and [[habitat destruction]]. Despite a lack of scientific studies or clinical trials,<ref name="Quackwatch">{{cite web |url=http://www.quackwatch.org/01QuackeryRelatedTopics/acu.html |author=Stephen Barrett, M.D. |title=Be Wary of Acupuncture, Qigong, and "Chinese Medicine" |date=12 January 2011 |access-date=11 December 2013}}</ref><ref>{{Cite journal |doi=10.1016/S0965-2299(03)00055-4 |pmid=12801499 |title=Use of animal products in traditional Chinese medicine: Environmental impact and health hazards |journal=Complementary Therapies in Medicine |volume=11 |issue=2 |pages=118–22 |year=2003 |last1=Still |first1=J.}}</ref> the consumption of seahorses is widespread in [[traditional Chinese medicine]], primarily in connection with [[impotence]], wheezing, [[nocturnal enuresis]], and pain, as well as [[labor induction]].<ref name=Bensky>Bensky, D., Clavey, S., Stoger, E. (2004) [http://www.eastlandpress.com/preview/ht.pdf ''Chinese Herbal Medicine: Materia Medica'']. Eastland Press, Inc.  Seattle, 3rd ed. {{ISBN|0939616424}}. p. 815</ref>  Up to 20 million seahorses may be caught each year to be sold for such uses.<ref>[https://www.pbs.org/wgbh/nova/seahorse/vincent.html "Seahorse Crusader Amanda Vincent"] on ''Nova'' television show</ref> Preferred species of seahorses include ''[[Great seahorse|H.&nbsp;kellogii]], [[Hippocampus histrix|H.&nbsp;histrix]], [[Hippocampus kuda|H.&nbsp;kuda]], [[Hippocampus trimaculatus|H.&nbsp;trimaculatus]],'' and ''[[Japanese seahorse|H.&nbsp;mohnikei]]''.<ref name=Bensky /> Seahorses are also consumed by [[Indonesia]]ns, central [[Filipino people|Filipinos]], and many other ethnic groups.{{Citation needed|date=August 2019|reason=Please cite reliable ethnographic sources for this claim.}}

Import and export of seahorses has been controlled under [[Convention on the International Trade in Endangered Species of Wild Flora and Fauna|CITES]] since 15 May 2004. However, Indonesia, Japan, Norway, and South Korea have chosen to opt out of the trade rules set by CITES.<!--dead <ref>
[http://seahorse.fisheries.ubc.ca/reservations.html Fisheries.UBC.ca], A new hurdle for seahorses – Project Seahorse{{Dead link|date=November 2009}}</ref>-->

The problem may be exacerbated by the growth of pills and capsules as the preferred method of ingesting seahorses. Pills are cheaper and more available than traditional, individually tailored prescriptions of whole seahorses, but the contents are harder to track. Seahorses once had to be of a certain size and quality before they were accepted by [[Traditional Chinese medicine|TCM]] practitioners and consumers. Declining availability of the preferred large, pale, and smooth seahorses has been offset by the shift towards prepackaged preparations, which makes it possible for TCM merchants to sell previously unused, or otherwise undesirable juvenile, spiny, and dark-coloured animals. Dried seahorse retails from US$600 to $3000 per kilogram, with larger, paler, and smoother animals commanding the highest prices. In terms of value based on weight, seahorses retail for more than the price of silver and almost that of gold in Asia.<ref>{{cite web |url=http://www.saveourseahorses.org/the-seahorse-dilemma.php |title=Save Our Seahorses |publisher=Save Our Seahorses |access-date=13 May 2014}}</ref>

== Conservation ==
Seahorses are iconic and charismatic animals whose conservation is of global concern.<ref>{{Cite journal |last1=Vincent |first1=A. C. J. |last2=Foster |first2=S. J. |last3=Koldewey |first3=H. J. |date=June 2011 |title=Conservation and management of seahorses and other Syngnathidae |url=https://onlinelibrary.wiley.com/doi/10.1111/j.1095-8649.2011.03003.x |journal=Journal of Fish Biology |language=en |volume=78 |issue=6 |pages=1681–1724 |doi=10.1111/j.1095-8649.2011.03003.x |pmid=21651523 |issn=0022-1112}}</ref> Preserving seahorses' varied habitats, including seagrass beds (such as ''Posidonia oceanica'' and ''Zostera marina''), mangroves, coral reefs, estuaries, seaweeds, and all the creatures that inhabit them, is closely related to protecting seahorses. Owing to their widespread use in collective imagery, these fish are popular wildlife viewing destinations, frequently serve as flagship species for international conservation campaigns, and are especially good at attracting public engagement in community scientific projects. According to Woodall et al.,<ref>{{Cite journal |last1=Woodall |first1=Lucy C. |last2=Otero-Ferrer |first2=Francisco |last3=Correia |first3=Miguel |last4=Curtis |first4=Janelle M. R. |last5=Garrick-Maidment |first5=Neil |last6=Shaw |first6=Paul W. |last7=Koldewey |first7=Heather J. |date=January 2018 |title=A synthesis of European seahorse taxonomy, population structure, and habitat use as a basis for assessment, monitoring and conservation |journal=Marine Biology |language=en |volume=165 |issue=1 |page=19 |doi=10.1007/s00227-017-3274-y |issn=0025-3162 |pmc=5717113 |pmid=29238097}}</ref> these creatures are susceptible to anthropogenic activities such as habitat degradation brought on by residential, commercial, and touristic coastal development, as well as accidental bycatch from damaging fishing equipment like dredges and trawls. There is little ecological data on seahorses because of their low population, seemingly dispersed location, and cryptic behavior.<ref>{{Cite journal |last1=Foster |first1=S. J. |last2=Vincent |first2=A. C. J. |date=July 2004 |title=Life history and ecology of seahorses: implications for conservation and management |url=https://onlinelibrary.wiley.com/doi/10.1111/j.0022-1112.2004.00429.x |journal=Journal of Fish Biology |language=en |volume=65 |issue=1 |pages=1–61 |doi=10.1111/j.0022-1112.2004.00429.x |issn=0022-1112}}</ref> Because of all these traits, seahorses are especially difficult to survey, assess, and monitor in order to enhance their conservation status. Conservation of these fishes depends on an understanding of their threats, distribution, and preferred habitats, which necessitates a thorough understanding of their regional ranges.<ref name=":0">{{Cite journal |last1=Bosso |first1=Luciano |last2=Panzuto |first2=Raffaele |last3=Balestrieri |first3=Rosario |last4=Smeraldo |first4=Sonia |last5=Chiusano |first5=Maria Luisa |last6=Raffini |first6=Francesca |last7=Canestrelli |first7=Daniele |last8=Musco |first8=Luigi |last9=Gili |first9=Claudia |date=2024-03-01 |title=Integrating citizen science and spatial ecology to inform management and conservation of the Italian seahorses |journal=Ecological Informatics |volume=79 |pages=102402 |doi=10.1016/j.ecoinf.2023.102402 |issn=1574-9541|doi-access=free }}</ref> Finding hotspots and possible hazards, as well as confirming their existence, actually depends on getting a good resolution of their presence and movement to carry out maps on their distribution.<ref name=":0" /> Maps can be used to assess future seahorse datasets and to pinpoint regions of study interest where more information can be gathered about the presence, quantity, habitat choice, influence of human activities, and status of seahorses.<ref name=":0" />

==Species==
On the basis of the newest overall taxonomic review<ref>{{Cite journal|last1=Lourie|first1=Sara A.|last2=Pollom |first2=Riley A.|last3=Foster|first3=Sarah J.|date=2016-08-01|title=A global revision of the Seahorses ''Hippocampus'' Rafinesque 1810 (Actinopterygii: Syngnathiformes): Taxonomy and biogeography with recommendations for further research |journal=Zootaxa |volume=4146 |issue=1 |pages=1–66|issn=1175-5334 |doi=10.11646/zootaxa.4146.1.1|pmid=27515600}}</ref> of the genus ''Hippocampus'' with further new species and partial taxonomic review,<ref name="Short-2018">{{Cite journal |last1=Short |first1=Graham |last2=Smith |first2=Richard |last3=Motomura |first3=Hiroyuki |last4=Harasti |first4=David |last5=Hamilton |first5=Healy |date=2018-08-02|title=''Hippocampus japapigu'', a new species of pygmy seahorse from Japan, with a redescription of ''H. pontohi'' (Teleostei, Syngnathidae) |journal=ZooKeys|issue=779 |pages=27–49 |doi=10.3897/zookeys.779.24799 |pmid=30166895 |pmc=6110155 |url=https://zookeys.pensoft.net/articles.php?id=24799 |issn=1313-2970|doi-access=free|bibcode=2018ZooK..779...27S }}</ref><ref name="Zhang-2016">{{Cite journal|last1=Zhang|first1=Yan-Hong |last2=Qin|first2=Geng|last3=Wang|first3=Xin|last4=Lin|first4=Qiang|date=2016-09-23|title=A new species of seahorse (Teleostei: Syngnathidae) from the South China Sea |journal=Zootaxa |volume=4170|issue=2|pages=384–392 |doi=10.11646/zootaxa.4170.2.11|pmid=27701270|issn=1175-5334}}</ref><ref name="Han-2017">{{Cite journal |last1=Han|first1=Sang-Yun|last2=Kim|first2=Jin-Koo|last3=Kai|first3=Yoshiaki|last4=Senou|first4=Hiroshi |date=2017-10-30 |title=Seahorses of the ''Hippocampus coronatus'' complex: taxonomic revision, and description of ''Hippocampus haema'', a new species from Korea and Japan (Teleostei, Syngnathidae) |url=https://zookeys.pensoft.net/articles.php?id=14955 |journal=ZooKeys|issue=712|pages=113–139 |doi=10.3897/zookeys.712.14955 |issn=1313-2970|pmc=5704180|pmid=29187790|doi-access=free|bibcode=2017ZooK..712..113H }}</ref><ref name="Short-2020">{{Cite journal |last1=Short |first1=Graham |last2=Claassens |first2=Louw |last3=Smith |first3=Richard |last4=De Brauwer |first4=Maarten |last5=Hamilton |first5=Healy |last6=Stat |first6=Michael |last7=Harasti |first7=David |date=2020-05-19 |title=''Hippocampus nalu'', a new species of pygmy seahorse from South Africa, and the first record of a pygmy seahorse from the Indian Ocean (Teleostei, Syngnathidae) |url= https://zookeys.pensoft.net/article/50924/ |journal=ZooKeys |issue=934 |pages=141–156 |doi=10.3897/zookeys.934.50924 |pmid=32508498 |pmc=7253503 |doi-access=free|bibcode=2020ZooK..934..141S }}</ref> the number of recognized species in this genus is considered to be 46 (retrieved May 2020):
[[File:Hippocampus kuda (Estuary seahorse).jpg|thumb|upright=0.8|''[[Hippocampus kuda|H. kuda]]'', known as the "common seahorse"]]
[[File:Hippocampus elongatus.jpg|thumb|upright=0.8|''[[Hippocampus subelongatus|H. subelongatus]]'', known as the "West Australian seahorse"]]
[[File:Hippocampus whitei 1.jpg|thumb|upright=0.8|''[[Hippocampus whitei|H. whitei]]'', known as "White's seahorse"]]
* ''[[Hippocampus abdominalis]]'' <small>[[René Primevère Lesson|Lesson]], 1827</small> (big-belly seahorse)
* ''[[Hippocampus algiricus]]'' <small>[[Johann Jakob Kaup|Kaup]], 1856</small> (West African seahorse)
* ''[[Hippocampus angustus]]'' <small>[[Albert Günther|Günther]], 1870</small> (narrow-bellied seahorse)
* ''[[Hippocampus barbouri]]'' <small>[[David Starr Jordan|Jordan]] & [[Robert Earl Richardson|Richardson]], 1908</small> (Barbour's seahorse)
* ''[[Hippocampus bargibanti]]'' <small>[[Gilbert Percy Whitley|Whitley]], 1970</small> (pygmy seahorse)
* ''[[Hippocampus breviceps]]'' <small>[[Wilhelm Peters|Peters]], 1869</small> (short-headed seahorse)
* ''[[Hippocampus camelopardalis]]'' <small>[[Giovanni Giuseppe Bianconi|Bianconi]], 1854</small> (giraffe seahorse)
* ''[[Hippocampus capensis]]'' <small>[[George Albert Boulenger|Boulenger]], 1900</small> (Knysna seahorse)
* ''[[Hippocampus casscsio]]'' <small>Zhang, Qin, Wang & Lin, 2016</small><ref name="Zhang-2016" /> (Beibu Bay seahorse)
* ''[[Hippocampus colemani]]'' <small>[[Rudie Hermann Kuiter|Kuiter]], 2003</small> (Coleman's pygmy seahorse)
* ''[[Hippocampus comes]]'' <small>[[Theodore Edward Cantor|Cantor]], 1850</small> (tiger-tail seahorse)
* ''[[Hippocampus coronatus]]'' <small>[[Coenraad Jacob Temminck|Temminck]] & [[Hermann Schlegel|Schlegel]], 1850</small> (crowned seahorse)
* ''[[Hippocampus curvicuspis]]'' <small>Fricke, 2004</small> (New Caledonian seahorse)
* ''[[Hippocampus dahli]]'' <small>[[James Douglas Ogilby|J. D. Ogilby]], 1908</small> (lowcrown seahorse)
* ''[[Hippocampus debelius]]'' <small>[[Martin F. Gomon|Gomon]] & [[Rudie Hermann Kuiter|Kuiter]], 2009</small> (softcoral seahorse)
* ''[[Hippocampus denise]]'' <small>[[Sara A. Lourie|Lourie]] & [[John Ernest Randall|Randall]], 2003</small> (Denise's pygmy seahorse)
* ''[[Hippocampus erectus]]'' <small>[[George Perry (naturalist)|Perry]], 1810</small> (lined seahorse)
* ''[[Hippocampus fisheri]]'' <small>[[David Starr Jordan|Jordan]] & [[Barton Warren Evermann|Evermann]], 1903</small> (Fisher's seahorse)
* ''[[Hippocampus guttulatus]]'' <small>[[Georges Cuvier|Cuvier]], 1829</small> (long-snouted seahorse)
* ''[[Hippocampus haema]]'' <small>Han, Kim, Kai & [[Hiroshi Senou|Senou]], 2017</small><ref name="Han-2017" /> (Korean seahorse)
* ''[[Hippocampus hippocampus]]'' <small>([[Carl Linnaeus|Linnaeus]], 1758)</small> (short-snouted seahorse)
* ''[[Hippocampus histrix]]'' <small>[[Johann Jakob Kaup|Kaup]], 1856</small> (spiny seahorse)
* ''[[Hippocampus ingens]]'' <small>[[Charles Frédéric Girard|Girard]], 1858</small> (Pacific seahorse)
* ''[[Japanese pygmy seahorse|Hippocampus japapigu]]'' <small>[[Graham Short (ichthyologist)|Short]], [[Richard Smith (ichthyologist)|R. Smith]], [[Hiroyuki Motomura|Motomura]], [[David Harasti|Harasti]] & [[Healy Hamilton|H. Hamilton]], 2018</small><ref name="Short-2018" /> (Japanese pygmy seahorse)
* ''[[Hippocampus jayakari]]'' <small>[[George Albert Boulenger|Boulenger]], 1900</small> (Jayakar's seahorse)
* ''[[Hippocampus jugumus]]'' <small>[[Rudie Hermann Kuiter|Kuiter]], 2001</small> (collared seahorse)
* ''[[Hippocampus kelloggi]]'' <small>[[David Starr Jordan|Jordan]] & [[John Otterbein Snyder|Snyder]], 1901</small> (great seahorse)
* ''[[Hippocampus kuda]]'' <small>[[Pieter Bleeker|Bleeker]], 1852</small> (spotted seahorse)
* ''[[Hippocampus minotaur]]'' <small>[[Martin F. Gomon|Gomon]], 1997</small> (bullneck seahorse)
* ''[[Hippocampus mohnikei]]'' <small>[[Pieter Bleeker|Bleeker]], 1854</small> (Japanese seahorse)
* ''[[Hippocampus nalu]]'' <small>[[Graham Short (ichthyologist)|Short]], [[Louw Claassens|Claassens]], [[Richard Smith (ichthyologist)|R. Smith]], [[Maarten De Brauwer|De Brauwer]], [[Healy Hamilton|H. Hamilton]], [[Michael Stat|Stat]] & [[David Harasti|Harasti]], 2020</small><ref name="Short-2020" /> (South African pygmy seahorse or Sodwana pygmy seahorse)
* ''[[Hippocampus paradoxus]]'' <small>[[Ralph Foster (ichthyologist)|Foster]] & [[Martin F. Gomon|Gomon]], 2010</small> (paradoxical seahorse)
* ''[[Hippocampus patagonicus]]'' <small>[[Gabriela Laura Maria Piacentino|Piacentino]] & [[Diego César Luzzatto|Luzzatto]], 2004</small> (Patagonian seahorse)
* ''[[Hippocampus planifrons]]'' <small>Peters, 1877</small> (flatface seahorse, false-eye seahorse)
* ''[[Hippocampus pontohi]]'' <small>[[Sara A. Lourie|Lourie]] & [[Rudie Hermann Kuiter|Kuiter]], 2008</small> (Pontoh's pygmy seahorse)
* ''[[Hippocampus pusillus]]'' <small>[[Ronald Fricke|Fricke]], 2004</small> (pygmy thorny seahorse)
* ''[[Hippocampus reidi]]'' <small>[[Isaac Ginsburg|Ginsburg]], 1933</small> (longsnout seahorse)
* ''[[Hippocampus satomiae]]'' <small>[[Sara A. Lourie|Lourie]] & [[Rudie Hermann Kuiter|Kuiter]], 2008</small> (Satomi's pygmy seahorse)
* ''[[Hippocampus sindonis]]'' <small>[[David Starr Jordan|Jordan]] & Snyder, 1901</small> (Sindo's seahorse)
* ''[[Hippocampus spinosissimus]]'' <small>[[Max Carl Wilhelm Weber|Weber]], 1913</small> (hedgehog seahorse)
* ''[[Hippocampus subelongatus]]'' <small>[[Francis de Laporte de Castelnau|Castelnau]], 1873</small> (West Australian seahorse)
* ''[[Hippocampus trimaculatus]]'' <small>[[William Elford Leach|Leach]], 1814</small> (longnose seahorse)

* ''[[Hippocampus tristis]]'' <small>Castelnau, 1872</small> (Lazarus Seahorse) <ref>Kuiter, R.H. (2020) Hippocampus tristis, a Lazarus species of seahorse (Teleostei: Syngnathidae) from Australia. Journal of the Ocean Science Foundation, 35, 41–47.; doi: https://doi.org/10.5281/zenodo.3905279</ref><ref>Castelnau, F.L. (1872) Contribution to the ichthyology of Australia –The Melbourne fish market. Proceedings of the Zoological and Acclimatisation Society of Victoria, Melbourne, 1, 29–242.</ref>
* ''[[Hippocampus tyro]]'' <small>[[John Ernest Randall|Randall]] & [[Sara A. Lourie|Lourie]], 2009</small> (Tyro seahorse)
* ''[[Hippocampus waleananus]]'' <small>[[Martin F. Gomon|Gomon]] & [[Rudie Hermann Kuiter|Kuiter]], 2009</small><ref name="Short-2018" /> (Walea soft coral pygmy seahorse)
* ''[[Hippocampus whitei]]'' <small>[[Pieter Bleeker|Bleeker]], 1855</small> (White's seahorse)
* ''[[Hippocampus zebra]]'' <small>[[Gilbert Percy Whitley|Whitley]], 1964</small> (zebra seahorse)
* ''[[Hippocampus zosterae]]'' <small>[[David Starr Jordan|Jordan]] & Gilbert, 1882</small> (dwarf seahorse)

==Pygmy seahorses==
[[File:HSatomiaeJohnSear.jpg|thumb|right|''[[Hippocampus satomiae]]'' (Satomi's pygmy seahorse) attached to coral]]
{{Main|Hippocampinae}}
Pygmy seahorses are those members of the genus that are less than {{convert|15|mm|in|frac=16|abbr=on}} tall and {{convert|17|mm|in|frac=16|abbr=on}} wide. Previously the term was applied exclusively to the species ''[[Hippocampus bargibanti|H.&nbsp;bargibanti]]'' but since 1997, discoveries have made this usage obsolete. The species ''[[Hippocampus minotaur|H.&nbsp;minotaur]]'', ''[[Hippocampus denise|H.&nbsp;denise]]'', ''[[Hippocampus colemani|H.&nbsp;colemani]]'', ''[[Hippocampus pontohi|H.&nbsp;pontohi]]'', ''[[Hippocampus severnsi|H.&nbsp;severnsi]]'', ''[[Hippocampus satomiae|H.&nbsp;satomiae]]'', ''[[Hippocampus waleananus|H.&nbsp;waleananus]]'', ''[[Hippocampus nalu|H.&nbsp;nalu]]'', ''[[Hippocampus japapigu|H.&nbsp;japapigu]]'' have been described. Other species that are believed to be [[biological classification|unclassified]] have also been reported in books, dive magazines and on the Internet. They can be distinguished from other species of seahorse by their 12 trunk rings, low number of tail rings (26–29), the location in which young are brooded in the trunk region of males and their extremely small size.<ref name="Lourie and Kuiter">{{cite journal|last=Lourie|first=Sara|author2=Rudie Kuiter |year=2008|title=Three new pygmy seahorse species from Indonesia (Teleostei: Syngnathidae: ''Hippocampus'')|journal=Zootaxa|volume=1963|pages=54–68|issn=1175-5334|url=http://www.mapress.com/zootaxa/2008/f/zt01963p068.pdf |archive-url=https://web.archive.org/web/20101204132352/http://www.mapress.com/zootaxa/2008/f/zt01963p068.pdf |archive-date=2010-12-04 |url-status=live|access-date=9 June 2009|doi=10.11646/zootaxa.1963.1.4}}</ref> Molecular analysis (of [[ribosomal RNA]]) of 32 ''Hippocampus'' species found that ''H.&nbsp;bargibanti'' belongs in a separate [[clade]] from other members of the genus and therefore that the species diverged from the other species in the ancient past.<ref name=Teske-2004/>

Most pygmy seahorses are well camouflaged and live in close association with other organisms including colonial [[hydrozoan]]s (''[[Lytocarpus]]'' and ''[[Antennellopsis]]''), [[coralline algae]] (''[[Halimeda]]''), and [[sea fan]]s (''[[Muricella]]'', ''[[Annella]]'', and ''[[Acanthogorgia]]''). This combined with their small size accounts for why most species have only been noticed and classified since 2001.<ref name="Lourie and Kuiter" />

==References==
{{Reflist|30em}}

==Further reading==
{{EB1911 Poster|Sea-horse}}
{{Refbegin|30em}}
*{{cite journal |doi=10.1016/0003-3472(95)80011-5 |first1=Amanda C.J. |last1=Vincent |first2=Laila M. |last2=Sadler |title=Faithful pair bonds in wild seahorse, ''Hippocampus whitei'' |journal=Animal Behaviour |volume=50 |pages=1557–69 |year=1995 |issue=6 |s2cid=53192875 }}
*{{cite journal |doi=10.1016/0003-3472(95)80178-2 |first1=Amanda C.J. |last1=Vincent |title=A role for daily greetings in maintaining seahorse pair bonds |journal=Animal Behaviour |volume=49 |pages=258–260 |year=1995 |s2cid=54391512 }}
*{{cite journal |first1=Amanda C.J. |last1=Vincent |title=A seahorse father makes a good mother |journal=Natural History |volume=12 |pages=34–43 |year=1990}}
*{{cite journal |doi=10.1016/0169-5347(94)90033-7 |first1=Amanda C.J. |last1=Vincent |first2=Rosie |last2=Woodroffe |title=Mothers little helpers: patterns of male care in mammals |journal=Trends in Ecology and Evolution |volume=9 |pages=294–7 |year=1994 |issue=8 |pmid=21236858 |bibcode=1994TEcoE...9..294W }}
*{{cite book |first1=John |last1=Sparks |title=Battle of the Sexes: The Natural History of Sex |url=https://archive.org/details/battleofsexesthe00spar |url-access=registration |publisher=BBC Books |location=London |year=1999 |isbn=978-0-563-37145-8 }}
*{{Cite journal |last1=Teske |first1=Peter R. |last2=Hamilton |first2=Healy |last3=Matthee |first3=Conrad A. |last4=Barker |first4=Nigel P. |date=2007-08-15 |title=Signatures of seaway closures and founder dispersal in the phylogeny of a circumglobally distributed seahorse lineage |journal=BMC Evolutionary Biology |volume=7 |issue=1 |pages=138 |doi=10.1186/1471-2148-7-138 |issn=1471-2148 |pmc=1978501 |pmid=17697373 |doi-access=free |bibcode=2007BMCEE...7..138T }}
{{Refend}}

{{Taxonbar|from=Q74363}}
{{Animal sexual behavior}}
{{Authority control}}

[[Category:Seahorses| ]]
[[Category:Taxa named by Constantine Samuel Rafinesque]]
[[Category:Extant Miocene first appearances]]