Seahorse

Hippocampus Temporal range: Lower Miocene to Present
Hippocampus sp.
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	Syngnathiformes
Family:	Syngnathidae
Genus:	Hippocampus Cuvier, 1816

Seahorses are a type of teleost fish. They are in the genus Hippocampus. They are called 'seahorses' because their head looks like a horse's head. There are about 32–48 species of seahorse. Seahorses live in tropical oceans.

Seahorses use camouflage to hide.^[1]

The earliest known seahorse fossils are H. sarmaticus and H. slovenicus.

Seahorses are unique because the male hatches the eggs in a pouch on his belly.^[1] The female inserts her ovipositor into the male’s brood pouch. She places dozens to thousands of eggs in the pouch. As the female releases her eggs, her body slims while his swells. The male releases his sperm directly into the water. The sperm then fertilize the eggs in the pouch. The fertilised eggs are then embedded in the pouch wall.^[1] They get nutrition and oxygen from the fluid in the pouch. In the pouch, the salinity of the water is controlled. This prepares the newborns for life in the sea.^[1]

Both animals then sink back into the seagrass and she swims away. The eggs then hatch ^[2][3]

Throughout gestation, which in most species requires two to four weeks, his mate visits him daily for 'morning greetings'. They interact for about 6 minutes. The female then swims away until the next morning, and the male vacuums up food through his snout.^[2]

Research published in 2007 shows that the males release sperm into the surrounding sea water during fertilization, and not directly into the pouch as previously thought.^[4]

The number of young released by the male seahorse averages 100-200 for most species, but may be as low as 5 for the smaller species, or as high as 1,500.

When the fry are ready to be born, the male expels them with muscular contractions. He 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 take care of 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 bodies. Fewer than 0.5% of infants survive to adulthood. This is why litters are so large. These survival rates are actually fairly high compared to other fish, because of their protected gestation. This makes the process worth the cost to the father. The eggs of most other fish are abandoned immediately after fertilization.^[3]

Seahorses are the only fish that experience true male pregnancy. ^[3]

There are 46 species in this genus:

• Hippocampus abdominalis Lesson, 1827 (big-belly seahorse)
• Hippocampus algiricus Kaup, 1856 (West African seahorse)
• Hippocampus angustus Günther, 1870 (narrow-bellied seahorse)
• Hippocampus barbouri Jordan & Richardson, 1908 (Barbour's seahorse)
• Hippocampus bargibanti Whitley, 1970 (pygmy seahorse)
• Hippocampus breviceps Peters, 1869 (short-headed seahorse)
• Hippocampus camelopardalis Bianconi, 1854 (giraffe seahorse)
• Hippocampus capensis Boulenger, 1900 (Knysna seahorse)
• Hippocampus casscsio Zhang, Qin, Wang & Lin, 2016 (Beibu Bay seahorse)
• Hippocampus colemani Kuiter, 2003 (Coleman's pygmy seahorse)
• Hippocampus comes Cantor, 1850 (tiger-tail seahorse)
• Hippocampus coronatus Temminck & Schlegel, 1850 (crowned seahorse)
• Hippocampus curvicuspis Fricke, 2004 (New Caledonian seahorse)
• Hippocampus dahli J. D. Ogilby, 1908 (lowcrown seahorse)
• Hippocampus debelius Gomon & Kuiter, 2009 (softcoral seahorse)
• Hippocampus denise Lourie & Randall, 2003 (Denise's pygmy seahorse)
• Hippocampus erectus Perry, 1810 (lined seahorse)
• Hippocampus fisheri Jordan & Evermann, 1903 (Fisher's seahorse)
• Hippocampus guttulatus Cuvier, 1829 (long-snouted seahorse)
• Hippocampus haema Han, Kim, Kai & Senou, 2017 (Korean seahorse)
• Hippocampus hippocampus (Linnaeus, 1758) (short-snouted seahorse)
• Hippocampus histrix Kaup, 1856 (spiny seahorse)
• Hippocampus ingens Girard, 1858 (Pacific seahorse)
• Hippocampus japapigu Short, R. Smith, Motomura, Harasti & H. Hamilton, 2018 (Japanese pygmy seahorse)
• Hippocampus jayakari Boulenger, 1900 (Jayakar's seahorse)
• Hippocampus jugumus Kuiter, 2001 (collared seahorse)
• Hippocampus kelloggi Jordan & Snyder, 1901 (great seahorse)
• Hippocampus kuda Bleeker, 1852 (spotted seahorse)
• Hippocampus minotaur Gomon, 1997 (bullneck seahorse)
• Hippocampus mohnikei Bleeker, 1854 (Japanese seahorse)
• Hippocampus nalu Short, Claassens, R. Smith, De Brauwer, H. Hamilton, Stat & Harasti, 2020 (South African pygmy seahorse or Sodwana pygmy seahorse)
• Hippocampus paradoxus Foster & Gomon, 2010 (paradoxical seahorse)
• Hippocampus patagonicus Piacentino & Luzzatto, 2004 (Patagonian seahorse)
• Hippocampus planifrons Peters, 1877 (flatface seahorse, false-eye seahorse)
• Hippocampus pontohi Lourie & Kuiter, 2008 (Pontoh's pygmy seahorse)
• Hippocampus pusillus Fricke, 2004 (pygmy thorny seahorse)
• Hippocampus reidi Ginsburg, 1933 (longsnout seahorse)
• Hippocampus satomiae Lourie & Kuiter, 2008 (Satomi's pygmy seahorse)
• Hippocampus sindonis Jordan & Snyder, 1901 (Sindo's seahorse)
• Hippocampus spinosissimus Weber, 1913 (hedgehog seahorse)
• Hippocampus subelongatus Castelnau, 1873 (West Australian seahorse)
• Hippocampus trimaculatus Leach, 1814 (longnose seahorse)
• Hippocampus tyro Randall & Lourie, 2009 (Tyro seahorse)
• Hippocampus waleananus Gomon & Kuiter, 2009 (Walea soft coral pygmy seahorse)
• Hippocampus whitei Bleeker, 1855 (White's seahorse)
• Hippocampus zebra Whitley, 1964 (zebra seahorse)
• Hippocampus zosterae Jordan & Gilbert, 1882 (dwarf seahorse)

Seahorses exhibit four phases of courtship.

This initial courtship takes place about 30 minutes after dawn on each courtship day. In 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.

This phase begins with the female beginning her pointing posture, by leaning her body towards the male, who will lean away and quiver. It can last up to 54 minutes.

The third phase begins with the females brightening and assuming the pointing position. It lasts for 9 minutes.

The final phase includes 5–8 bouts of courtship. Each bout begins with both the male and female anchored to the same plant about 3 cm apart; usually they are facing each other and are still bright from the previous phase.