Seashores (or the Hippocampus sp.) are a unique set of creatures in the animal kingdom. Though they look quite strange in comparison to a normal fish, they are in fact fish, who swim rather vertically than horizontally. There are about 32 different species of seahorse and their sizes differ from 1 centimeter to 30 centimeters. They have prehensile tails to cling to underwater vegetation, a tubercle mouth for sucking in food and protective bony plates in their skins as a defensive mechanism.
Besides their strange looks, seahorses have one of the most unique reproductive habits in the animal world. Unlike all other creatures, it’s the male seahorse that gets pregnant and carries the maturing eggs around. Some scientists believe they mate for life (show monogamy), which is not a common practice among fish.
The mating ritual of the sea horses is known as courtship. It is so called as the male and female perform a dance up to eight hours in successive days before mating. The selection of partners is a strange business as well. Males, which are less in both size and color, fight with their snorts and wrestle with their tails to get a female partner. Females on the other hand, display bright colors to attract males.
Once the partners are selected, courtship begins. Here the male and female partners swim around side by side, holding each other’s tail and changing colors as they go. It is a glamorous site to watch if you ever get the chance to see it. This goes on for few days and up to eight hours. The use of the courtship is thought to be that it allows the partners to synchronize their movements during mating.
During mating, female seahorse using her ovipositor, inserts the eggs to the male’s brood pouch. Male release the sperms to the nearby sea water, which fertilizes the eggs as they enter into the pouch. Once the eggs get entered they get covered by a layer of spongy tissue. The female can deposit up to 1500-2000 eggs at a time, depending on the species. But she may not deposit all of them at once to avoid getting exhausted. The male take these intervals to adjust the eggs in place so that all the eggs can be accommodated in the pouch.
After the mating the female swims away while the male remains. The incubation period ranges from 9-45 days, again depending on the species. The males are known to become quite aggressive while they are pregnant and as any mother would do, male seahorses produce the needed microenvironment as well as the nutrients needed for the growth of their offspring. The female visits the male each day and make sure that the eggs are developing alright. After the incubation period the male develop muscular contractions and swings back and forth as the newborns are ejected from the pouch. The newborns are miniature models of the adults and are called fry. Fries are released all over the place where they struggle to survive to reach maturity.
Neither the male nor the female take part in the upbringing of the fries after they leave the pouch. Most of the fries die, either being eating by many predators or being carried away from the feeding grounds by the ocean currents. A single male may release around 100-200 fry at a time. This can be as low as 5 or high as 1500. But out of all these large numbers only about 5 out of 1000 fries reach maturity to become sexually active.
- Reasons for the Differences
It is not clear why the seahorses have developed such a unique way of reproduction. Some scientists believe that it gives them a special advantage to reproduce more rapidly. It takes some time for the female to produce eggs and this process also consumes a large amount of energy. The male has adapted to help the female in this process by sharing the energy expenditure and giving the species more advantage to survive. In fact, even though 5 out of 1000 survival rate remains quite low, it is still quite a higher number in the fish world.
The reproductive rate is quite high among seahorses. Males usually release fries during the night and by the next evening they are again seen pregnant with female eggs. It was earlier thought that the seahorses mate for life, but now scientists think that the couples only remain so during a single mating season. Form season to season, it is believed that they change partners. However, being a single couple during a single mating season, allows the seahorses to reproduce more effectively and rapidly as possible.
Seahorses are one of the miracles of all nature. They are quite spectacular to watch as well as amazing to study. The main threat for the seahorse population has come from humans who hunt them to use for various traditional medical products. It is a responsibility of everyone to save these majestic creatures for future generations as well.