Marine Biology

The Reproductive Process of Seahorses



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Seahorses are amongst the most easily recognised and popular species of marine life. However, these highly specialised creatures are full of surprises. Although they are closely related to pipefish, they exhibit several characteristics that are atypical of fish. They swim vertically, rather than horizontally, have a prehensile “tail” capable of grabbing underwater reads and grasses, and don’t have scales or teeth.

Perhaps the most interesting difference from run of the mill fish, or indeed from most other animals, is that the male plays the greater role in the reproductive process. Like other fish, the seahorse lays eggs - up to 1500 at a time depending on the species, but generally, the larger the species, the more eggs are laid. However, instead of laying eggs in a clutch into the relatively unprotected open ocean, the female seahorse deposits her eggs into a specialised brood pouch – located on the front side of the male.

The transfer of eggs is preceded by an elaborate courtship ritual that can last for several days. Initially, the pair will meet in an early morning “pre-dawn dance”, where they swim and interact together, often intertwining their tails. Eventually, they will start a sustained period of courtship over an eight-hour period, which scientists believe helps ensure that he partners are properly aligned for when the transfer of eggs takes place. At the end of the process, the eggs are deposited.

The male seahorse then fertilises the eggs. There appears to be some debate as to whether the eggs are fertilised directly in the pouch, or whether – like other fish – male reproductive cells are released into the water in close proximity to the female’s eggs. In any event, with the job done, the male will incubate the eggs until they hatch (a process that takes approximately two to six weeks) and will continue to provide for the young – supplying food and oxygen – until they are ready to be released.

The female will visit the male every morning during this period, ostensibly to check on the progress of her clutch. Until recently, it was believed that seahorses mate for life, however, recent research suggests that whilst they will stay monogamous during a particular breeding season, they do choose other mates in other seasons. Baby seahorses (known as “fry”) emerge as fully developed miniature versions of the parents.

Neither parent takes any further interest in the fry after they are expelled from the male seahorse’s brood pouch. They spend the first few weeks of their lives in the oceans plankton layer. Very few of the young survive to adulthood – which explains why the eggs are laid in such large quantities. That said, the incubation period gives them a better chance of survival than other fish, most of which abandon their eggs immediately after they are fertilised (the clownfish – made famous in “Finding Nemo”, being a notable exception).

The male will be ready for another batch of eggs almost as soon as the fry are expelled. There are a number of theories to explain why the male seahorse takes such a crucial role in reproduction. The most popular seems to be that sharing the energy and cost of producing young allows the female to prepare more eggs while the male incubates the current “litter”, ultimately helping to ensure the survival of this unique species.

Sources:

National Geographic (www.nationalgeographic.com)

The Seahorse Trust (http://www.theseahorsetrust.org)

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  • InfoBoxCallToAction ActionArrowhttp://www.nationalgeographic.com/
  • InfoBoxCallToAction ActionArrowhttp://www.theseahorsetrust.org/