Seahorses are strange-looking fish that resemble knights in a chess game and swims in an upright position. They are found in coral reefs, mangroves and particularly grass beds. They can be found in coastal area in most parts of the world south of Canada and north of Tasmania. The Giant Pacific seahorses is the largest seahorse. It reaches a length of 36 centimeters (14 inches). The smallest one is the size of a peanut. Seahorses belong to the pipefish family which includes about 295 species. [Source: Amanda Vincent, National Geographic, October 1994]
Seahorses are strange fish period. They look like a mix of other animals and it is the males give birth and take care of young not visa versa. Seahorses generally inhabit coastal waters, clinging to seagrasses, corals, and sponges. Pairs intertwine their tails for stability. In recent decades, some species of these unique fish have become threatened, mainly due to by overfishing and habitat loss, and still we don’t know very much about them. Originally, ancient Greek poets used the Greek word Hippocampus to describe a half-horse, half-fish mythical god. The description seemed apt of the fish’s horse-like head positioned 90 degrees from its upright, armor-plated body, curved trunk, and prehensile tail.
Seahorses inhabit various ecosystems and are viewed as a flagship species marine environments. Jennifer S. Holland wrote in National Geographic: Every continent but Antarctica has varieties of these fabled fish in its coastal waters. Worldwide, scientists recognize 46 species, and that number is likely to rise: Four new species were named in 2021. Seahorses, pipefish, and sea dragons belong to a family of fish known as Syngnathidae, a taxonomic group that includes 295 species. Family traits include long snouts, fused jaws, bony body armor, increased numbers of vertebrae, an elongated head, and missing pelvic fins and ribs. Males incubate eggs and a male brood pouch, which is unique to the family. Many species are good at camouflaging themselves. [Source: Jennifer S. Holland, National Geographic, March 15, 2022]
Websites and Resources: Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; Fishbase fishbase.se ; Encyclopedia of Life eol.org ; Smithsonian Oceans Portal ocean.si.edu/ocean-life-ecosystems ; Woods Hole Oceanographic Institute whoi.edu ; Cousteau Society cousteau.org ; Monterey Bay Aquarium montereybayaquarium.org ; MarineBio marinebio.org/oceans/creatures
Jennifer S. Holland wrote in National Geographic: It’s easy to see the seahorse’s allure, with its fanciful blend of traits that seem borrowed from other animals: a horse’s head, a chameleon’s independent eyes and camo skills, a kangaroo’s pouch, a monkey’s prehensile tail. Hippocampus comes in colors rivaling Crayola’s Big Box and in a multitude of bumps and blotches, stripes and speckles, spikes and lacy skin extensions. These sit-and-wait predators are dancers of a sort. During courtship, a pair rises and falls face-to-face in the water, communicating with color changes and tail embraces. They may tango for days and stay together for an entire season. [Source: Jennifer S. Holland, National Geographic, March 15, 2022]
Seahorses have monkey-like tails that can be used to grasp things. Their bodies are encased in bony ringlike plates studded with spines. Their coronets (crown of skin filaments) are as unique as finger prints. Their chameleon-like eyes move independently of one another. Sometimes one eye be on the look out for predators while the other is searching for food. Seahorses are generally very well camouflaged. Some turn bright yellow to send a warning to predators. Seahorses produce noise by rubbing their head against the spines on their back.
Sea horses are cold blooded (ectothermic, use heat from the environment and adapt their behavior to regulate body temperature), heterothermic (having a body temperature that fluctuates with the surrounding environment) and have bilateral symmetry (both sides of the animal are the same). Seahorse lengths are measured from the tip of the tail to the top of the coronet, a cup-like depression found on top of the head.
Seahorses lack typical physical features of fishes such as pelvic and caudal fins, teeth, and a stomach. The backbone structure is unlike that of other vertebrates, with knobby, bony plated rings extending along the tail to the trunk. This makes the tail prehensile and flexible, able to coil around seagrass and other objects. Seahorses also lack scales. Instead they have a layer of skin stretched over a series of bony plates which are visible as rings around the trunk. These visible rings are useful in identifying different Hippocampus species. Males can be distinguished from a female by the presence of a brooding pouch on his belly. [Source: Micheleen Hashikawa, Animal Diversity Web (ADW) /=]
Sea Horse Shape
A sea horse’s shape — a curved body and arched neck — may have evolved to help it snare prey, researchers say. Charles Q. Choi wrote in Live Science: Although they have long snouts like their close relatives the pipefish, their bent necks and curved trunks make them far different from their straight-bodied family. To understand how the seahorse's peculiar head, neck and trunk might have evolved, scientists analyzed how effective the animals were at capturing food when compared with pipefish. If a horselike shape provided the ancestors of sea horses an edge when it came to finding a meal, that could help explain why it developed, the investigators reasoned. [Source: Charles Q. Choi, LiveScience, January 26, 2011]
“Computer simulations revealed the shape and posture of sea horses helped them pivot forward to capture prey. High-speed video footage of both sea horses and pipefish corroborated these findings, revealing that sea horses can strike farther than pipefish. Interestingly, pygmy pipehorses have a prehensile tail like sea horses but lack the curved posture of their cousins. This suggests the development of a sit-and-wait lifestyle might have preceded the evolution of the bent head in sea horses.
"Once this shift in foraging behavior is made, natural selection will favor animals that can increase the strike distance, which according to our study puts a selective pressure to increase the angle between head and trunk and to become what we now know as sea horses," researcher Sam Van Wassenbergh, a biomechanicist at the University of Antwerp in Belgium, told LiveScience. The scientists detailed their findings online Jan. 25 in the journal Nature Communications.
Seahorse Swimming and Behavior
Seahorses are slow swimmers. Unlike other fish, they tend to swim in a vertical rather than horizontal position and seem avoid swimming as much as possible. Instead they wrap their tails around sea fans or grasses, waiting for small vertebrates to be carried their way by ocean currents. Sometime they cling to small blades of grass for days. When they do swim they do so with quick, fluttering dorsal fins movements. They don’t have conventional fish tails.
Jennifer S. Holland wrote in National Geographic: When a seahorse needs to move from here to there, it swims upright with the frantic flutter of its dorsal fin at up to 70 beats per second and steers with its pair of pectoral fins. To stay put, it uses its flexible tail to grab onto seagrass, coral, or other fixed items on the seafloor. The seahorse’s excellent camouflage then makes it all but invisible. [Source: Jennifer S. Holland, National Geographic, March 15, 2022]
Seahorses are generally solitary, except for their mates, and are active during the day. Because seahorses are poor swimmers they generally remain anchored to substrates using their prehensile tails. As a rule pairs pairs remain in close proximity to one another and avoid associations with non-pair individuals. [Source: Micheleen Hashikawa, Animal Diversity Web (ADW) /=]
Seahorses communicate with vision, touch and sound and sense using vision, touch, sound, vibrations and chemicals usually detected with smelling or smelling-like senses. Their lateral line system determines pressure and water movements around them. They rely on vision to accurately locate prey when it comes within sight and during courtship, and they possess olfactory nares, which can detect dissolved chemicals. They are also capable of hearing; a clicking sound is produced when mating pairs touch heads as part of courtship behavior.
They typically have narrow home ranges due to their poor swimming abilities.They tend to remain close to a holdfast such as a blade of seag rass within their territory. Holdfasts and home ranges are only changed in an event of a partner's death or habitat destruction. /=\
Seahorse Food and Feeding Behavior
Adult seahorses have big appetites and suck and swallow any animal that fits in their mouths, which are quite small. They feed on small shrimp, larval crustaceans and other zooplankton they suck in with their powerful tube-like snouts. They are preyed on by mollusks, crabs and some fish and seabirds. Many fish spit them out because they are too knobby and hard.
Seahorses are sit-and-wait predators who seem to prefer places where their camouflage hides them from predators and lot things they can eat float by. They don’t have a stomach to store food or teeth. Instead they suck in prey through their tube-like snouts. Some species and are almost constantly sucking up copepods, shrimp, fish larvae, and other tiny edible thing that come within range. They are able to maximize their perception of potential prey and predators by moving their eyes independently of each other.
The dwarf seahorse (Hippocampus zosterae) feeds on copepods. One study reported: Using phytoplankton as a tracer, we recorded and reconstructed 3D flow fields around the head of the seahorse and its prey during both successful and unsuccessful attacks to better understand how some attacks lead to capture with little or no detection from the copepod while others result in failed attacks. Attacks start with a slow approach to minimize the hydro-mechanical disturbance which is used by copepods to detect the approach of a potential predator. Successful attacks result in the seahorse using its pipette-like mouth to create suction faster than the copepod's response latency. As these characteristic scales of entrainment increase, a successful escape becomes more likely. [Source: “Predation by the Dwarf Seahorse on Copepods: Quantifying Motion and Flows Using 3D High Speed Digital Holographic Cinematography — When Seahorses Attack!” by Gemmell, Brad; Sheng, Jian; Buskey, Ed, 2008-11-01]
Male Seahorses and Their Reversed Sexual Roles
The female seahorses impregnate the males rather than via versa — an evolutionary trait unique to seahorses and members of the Syngnathidae family. Male seahorse carry the eggs of the female in a kangaroo-like pouch. Like other animals males carry sperm and females have eggs. The difference is that seahorse female deposits her eggs in a a pouch male's tail, where they mix with sperm, and the male gives "birth" to the baby seahorses.
Jennifer S. Holland wrote in National Geographic: The female deposits her yolk-rich eggs into his belly pouch through a port on her trunk called an ovipositor. Several weeks later the distended male goes into body-spasming labor, ejecting dozens to thousands of young — depending on the species’ size — into the current. Offspring drift awhile before settling down, and only a scant few avoid being eaten by predators in those early days. [Source: Jennifer S. Holland, National Geographic, March 15, 2022]
Even though male seahorses play a traditionally feminine role in raising young they generally play conventional sexual roles found in the animal kingdom. Males compete against one another for females rather than visa versa. Males fighting over a female generally bash each other with their snouts,
The male does most of the parenting even though the female visits him every morning until the young are born. The male provides the young in the pouch with most of the nutrients that females in other species provide their young in the uterus. The activity is stimulated by the hormone prolactin, which stimulates milk production in women.
Seahorses are generally monogamous in the mating season and many are monogamous for life although some species engage in promiscuous mating systems, such as polyandry and polygynandry but not many according to researcher. “They do flirt a lot, but they’re actually faithful,” Heather Koldewey, head of global conservation programs for the Zoological Society of London, told the Washington Post.“There’s a lot of behavior to suggest otherwise, but if you do the genetic analysis, it’s just all show.” Genetic studies of dwarf seahorses found that members of a pregnant male's brood had one mother and one father, indicating the species is genetically monogamous.
Seahorses couples greet each other by jointly wrapping their tails around a blade of sea grass, touching their snouts and quivering with pleasure. They go for strolls with their tails. Females often have larger territories than males. The home range of “whitei” seahorse is limited to a square meter. His female partner is about a hundred times that size. The difference reduces competition for food.
Spotted seahorses maintain a faithful association with only one partner. A new mate is sought only when a partner dies. The age at which female and male spotted seahorse reach sexual maturity is unknown. However the presence of a brooding pouch on the male — the site where the male carries the fertilized eggs — signifies male sexual maturity. Monogamous pairs can often be found coiled together or within close proximity to one another . Pairs communicate daily during male pregnancy to reinforce their relationship.
Seahorse Mating and Reproduction
Seahorses are ovoviviparous (eggs are hatched within the body of the individual that gives birth), in the cases of seahorses, the male. are iteroparous (offspring are produced in groups). They engage in internal reproduction in which sperm from the male parent fertilizes an egg from the female parent. They engage in year-round breeding.
About three or four days before mating, the males develops a pouch. During the mating ritual the male shows he is "receptive" by displaying his empty pouch. If the female is attracted, the couple copulates. The two then change colors and dance around each other for hours. During the five second mating process the male and female entwine their tails and the female squirts several thousand eggs into the pouch of the male, who releases sperm from special ducts that quickly fertilizes the eggs. The pouch lining secretes a nourishing fluid absorbed by the eggs.
According to Animal Diversity Web (ADW): Seahorses have a complex, a unique courtship ritual. The male begins by changing its color patterns as it dances around the female. It also produces clicking sounds with its coronet. The pair proceeds with the ritual by entwining their tails together and floating across the ocean floor. Eventually the male and female face each other belly-to-belly at which time the female places her eggs into the male’s brooding pouch with her ovipositor. This courtship ritual is modified and repeated daily even after the male has become pregnant. Each morning the pair comes together to dance, change colors, and entwine tails. [Source: Micheleen Hashikawa, Animal Diversity Web (ADW) /=]
During the pre-fertilization stage provisioning and protecting is done by females. Pre-birth provisioning and protecting are provided by the male. Males go into “labor”. The timing of labor in males varies depending upon species, water temperature, monsoon patterns, and lunar cycles. However, most males go into labor at night during a full moon. Males engage in vigorous pumping and thrusting motions for several hours to release the young. Newborn seahorses emerge from a male’s pouch, where a female deposited her eggs for incubation. This pot-bellied seahorse father may give birth to hundreds of young, most of which are gobbled up by predators.
Seahorse Young and Development
Seahorse eggs take about 21 days to incubate. About two weeks after they hatch from the eggs young seahorses are shot from the male’s pouch in spurts by muscle contractions. This process can go on for 24 hours or more and stops when all the babies — usually a thousand or more — are released. Regardless of species, all newborn seahorses are about a quarter to half inch in length. After they emerge the young curl their tail around the first thing they see. Juvenile seahorses rarely stray far from the home range of the parents.
According to Animal Diversity Web: Eggs are fertilized by the male and become embedded in the pouch wall as they are deposited into the brooding pouch by the female through the ovipositor The male may carry between 20 to 1000 eggs in its pouch. Although fertilized eggs contain a small amount of yolk, they undergo typical teleost egg cleavage and developmental processes, which lasts for approximately 20 to 28 days. Larval development stops one week prior to the time at which they are released into the open waters. In general juvenile seahorses can be distinguished from their adult counterparts by differences in body proportions. Young seahorses have larger heads, slimmer, spinier bodies, and higher coronets.
At birth, the short-snouted seahorse (Hippocampus hippocampus) has a mainly cartilaginous structure that ossifies in approximately one month. The bony armour composed of bony rings and plates develops in 10 days. The caudal fin, a structure absent in juveniles and adult seahorses, is present at birth and progressively disappears with age. The absence of adult osteological structure in newborns, like coronet, bony rings and plates, head spines and components allowing tail prehensile abilities, suggests a metamorphosis before the juvenile stage. During the indirect development, the metamorphic stage started inside brood pouch and followed outside and leads up to reconsider the status of H. hippocampus newborns. [Source: “Development of short-snouted seahorse (Hippocampus hippocampus, L. 1758): osteological and morphological aspects.” by Novelli, B; Otero-Ferrer, F; Socorro, J A; Caballero, M J; Segade-Botella, A; Molina DomÃ-nguez, L, 2017-06-01]
Study of Seahorses
Jennifer S. Holland wrote in National Geographic: For all their notoriety — who wouldn’t recognize a seahorse? — much about the fish remains little known, including where they live and precisely how their populations are faring. The International Union for Conservation of Nature (IUCN) Red List of Threatened Species includes all Hippocampus species, and many are listed as data deficient. [Source: Jennifer S. Holland, National Geographic, March 15, 2022]
“For the vast majority of species,” says marine biologist Amanda Vincent of the University of British Columbia (UBC), “beyond taxonomy and a basic description, we know almost nothing.” Vincent is the director of Project Seahorse, a conservation alliance between UBC, where Vincent is a professor at its Institute for the Oceans and Fisheries, and the Zoological Society of London. Such a knowledge gap, blamed in part on the dearth of scientists who study seahorses, is especially problematic for a fish that’s so exploited.
Another problem is they are often hard to find. On trying to find them on a dive, Holland wrote: Miguel Correia pointed at the seafloor. I stared and shook my head. He jabbed a gloved finger at the spot. I swam closer and stared harder. Sand. Algae. Rocks. A spiral of sea cucumber poop. I exhaled a swarm of bubbles in frustration...And then, suddenly, there it was, tucked into the seaweed right where I’d been looking: a three-inch-tall, long-snouted seahorse, Hippocampus guttulatus, muddied yellow with a smattering of dark freckles and a mane of skin filaments. Later that dive I spotted (also with help) its short-snouted cousin, Hippocampus hippocampus, the other seahorse native to this coastal lagoon in Portugal called Ria Formosa.
Image Sources: Wikimedia Commons; YouTube, Animal Diversity Web, NOAA
Text Sources: Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; Wikipedia, National Geographic, Live Science, BBC, Smithsonian, New York Times, Washington Post, Los Angeles Times, The New Yorker, Reuters, Associated Press, Lonely Planet Guides and various books and other publications.
Last Updated March 2023