Sea horse

seahorse (also written sea-horse and sea horse) is any of 46 species of small marine bony fish in the genus Hippocampus. "Hippocampus" comes from the Ancient Greek hippókampos (ἱππόκαμπος), itself from híppos (ἵππος) meaning "horse" and kámpos (κάμπος) meaning "sea monster"or "sea animal".

Having a head and neck suggestive of a horse, seahorses also feature segmented bony armour, an upright posture and a curled prehensile tail.

 Along with the pipefishes and seadragons (Phycodurus and Phyllopteryx) they form the family Syngnathidae.

HABITAT

• Seahorses are mainly found in shallow tropical and temperate salt water throughout the world, from about 45°S to 45°N.

• They live in sheltered areas such as seagrass beds, estuaries, coral reefs, and mangroves.

DESCRIPTION

• Seahorses range in size from 1.5 to 35 cm (0.6 to 13.8 in).

• They are named for their 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.

• The armor of bony plates also protects them against predators, and because of this outer skeleton, they no longer have ribs.

• Seahorses swim upright, propelling themselves using the dorsal fin, another characteristic not shared by their close pipefish relatives, which swim horizontally.

• The pectoral fins, 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.

• They are adept at camouflage, and can grow and reabsorb spiny appendages depending on their habitat.

• 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.

• Seahorses swim very poorly, rapidly fluttering a dorsal fin and using pectoral fins to steer. 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.

REPRODUCTION

• 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 eggs 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.

Courtship

• Before breeding, seahorses may court for several days.

• 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.

• 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.

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.

• 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.

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.

 Gestation

• The fertilized eggs are then embedded in the pouch wall and become surrounded by a spongy tissue.

• The pouch provides oxygen, 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.

• The eggs then hatch in the pouch, where the salinity of the water is regulated; this prepares the newborns for life in the sea.

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.

• When the 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.

MONOGAMY

• While seahorses are not typically lifelong mates, many species form pair bonds that last at least through the breeding season, with some showing more mate fidelity than others. However, species like H. abdominalis and H. breviceps breed in groups and show no continuous mate preference. The mating habits of many seahorse species remain unstudied, so the extent of monogamy and the duration of these bonds are largely unknown.

• Monogamy in fish is rare but does occur. The mate-guarding hypothesis suggests males stay with a single female due to ecological factors, making male parental care and offspring protection crucial. Because newborn seahorses have low survival rates, male incubation may have evolved to reduce the interval between clutches while females prepare their next set of eggs.

FEEDING HABITS

• Seahorses rely on stealth and pivot feeding to ambush small prey like copepods, using their long snouts to swiftly suck in prey. Due to their simple digestive systems, which lack a stomach, seahorses must eat constantly to survive.

• As poor swimmers, seahorses anchor themselves to seaweed, coral, or other objects using their prehensile tails. They feed on small crustaceans, including mysid shrimp, by camouflaging themselves and waiting for prey to come within striking range. Seahorses have a hydrodynamic head shape that allows them to approach prey with minimal disturbance.

• Seahorses capture prey using a two-phase mechanism called pivot-feeding. They first approach the prey slowly (preparatory phase), then elevate their head and suck in the prey (expansive phase), and finally return their jaws and head to their original position (recovery phase). The amount of vegetation in their environment influences their feeding strategy, with more cover prompting more active searching behavior.