Seahorse – Did You Know…

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… That every morning, the male and female seahorse come together for a “dance” to reinforce their bond?

Seahorses range in size from 1.5 to 35.5 cm (0.6 to 14.0 in). They are named for their equine appearance with bent necks and long snouted heads followed by their 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. Seahorses swim upright, another characteristic not shared by their close pipefish relatives, which swim horizontally. Razorfish are the only other fish that swim vertically like a seahorse. They swim upright propelling themselves by using the dorsal fin. The pectoral fins located on either side of the head are used for maneuvering. They lack the caudal fin typical of fishes. Their prehensile tail can only be unlocked in the most extreme conditions. Interestingly, they are adept at camouflage with the ability to 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 (located behind their eyes) to steer. The slowest-moving fish in the world is H. zosterae (the dwarf seahorse), with a top speed of about 5 ft (1.5 m) per hour. Seahorses have no caudal fin. Since they are poor swimmers, they are most likely to be found resting with their prehensile tails 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.

The male seahorse is equipped with a 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. Once the young are released into the water, the male’s role is done and he offers no further care and often mates again within hours or days during the breeding season.

Before breeding, seahorses may court for several days. Scientists believe the courtship behavior synchronizes the animals’ movements and reproductive states so 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 seagrass, often spiraling as they rise. They interact for about 6 minutes, reminiscent of courtship. The female then swims away until the next morning, and the male returns to sucking up food through his snout. 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 seagrass and she swims away.

After two to four weeks 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. 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.

 

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