THE COMPLEX REPRODUCTIVE PROCESS OF SEAHORSES

In today’s article we are going talk a little bit about the physiology, particularly in relation to the reproductive process, of one of the most unique genera of fishes there exisy. They are known as seahorses, which is the translation of their scientific name Hippocampus (from Greek hippos meaning “horse” and kampos meaning “sea monster”). The reason for this name is the fact that their head, neck and snout are shaped like those of horses.

They are usually found in shallow and warm saltwater areas around the world. Especially in places in which they can easily find shelter, such as coral reefs, mangroves, etc.

If you want to learn more about these fascinating and unique creatures, continue reading the article.

Seahorses vary greatly in size among the 45 species of the genus. They can be from about 0.6 to 14.0 in (1.5 to 35.5 cm) long. As I mentioned before, their head and neck shape reminded scientists of horses, therefore earning them their name. Unlike the vast majority of fishes, seahorses don’t have scales. Instead, they have bony plates under their skin. These are shaped like rings that surround the body and can be used for species identification. Their function is essentially protecting the individual from predatory attacks.

Photo by: Susanne Nilsson
https://creativecommons.org/licenses/by-sa/2.0/

Being really bad swimmers, seahorses are mostly found attached with their prehensile tail to seaweeds or corals. However, when they do swim, they do it in a very particular way. They swim upright and use their dorsal fin to propel themselves. To steer, they use their pectoral fins, which are quite small and are located on their sides. Despite being one of the most typical fish features, seahorses don’t have a caudal fin. What most people don’t know is that seahorses have camouflage skills. For example, they can grow and reabsorb spines to match their environment. Another interesting characteristic is that they can move their eyes independently, just like chameleons.

Probably the most amazing aspect of these creatures’ lives is their reproductive process. It consists on a very complex courtship period and amazing breeding, gestation and birth methods.

Their courtship is divided into four phases, each one more amazing than the previous.

The first phase lasts for one or two days before the breeding. Around thirty minutes after dawn, males brighten their colors. Then, both males and females make a side-to-side movement known as quivering.

When the day of the copulation arrives, a ritual consisting on phases two to four starts. In the second phase, the female leans towards the male as he leans away and quivers and makes a pumping motion. There’s a moment in which the male finally leans towards the female and they both are pointing at each other and brighten their colors. This is known as phase three. The fourth and final phase is the most amazing one, as the couple performs several courtship dances. They make up to eight ascending moves in a water column together and, in the final one, the female deposits the eggs in the male’s pouch.

Photo by: iulianescu78

When the courtship is finished and the male has the eggs, he fertilizes them. Although this process takes place in the pouch, which is an internal environment, it is considered external fertilization. This is because the eggs are in contact with the seawater, which is an external environment. Unlike most species in the animal kingdom, males are the ones which carry the eggs during the gestation period, even though females visit them every morning. The male’s pouch provides oxygen, a controlled environment, nutrients and residue transport.

When the time for the birth comes, the male performs a series of muscle contractions and expels from one hundred to one thousand young seahorses to the water. As most fishes, seahorses don’t provide post-birth nurture and only 0.5% of the young seahorses reach adulthood. Although this may look like very little, it is quite high among fishes, probably due to the internal protected gestation of the eggs.

After writing an article, I can’t help but feel amazed by the complexity and beauty of the amazing living organisms of our planet. In the end, these articles help me organize my ideas and remind me of how amazing nature is. Seahorses have a very peculiar and complex reproductive process that has caught the eye of thousands of researchers and it isn’t a surprise. It is just fascinating how every being has a different method to achieve similar goals, don’t you think?