Seahorses are one of the weirdest creatures on the planet. They are basically fish, but they don’t look or act like most fish. They swim upright rather than horizontally. As if that wasn’t weird enough, it’s male seahorses – not females – that carry and give birth to babies. To find out why they are so weird, a team of international researchers has sequenced the seahorse genome for the first time.

Seahorse genome
Image Credit: Oscar Alexander / Flickr

Seahorses are unique in more than one way

Findings of the study were published in the journal Nature. Scientists believe the genome could help explain why the seahorse is so unique. There are 47 known species of seahorses, and they are found in coastal waters around the world. They don’t have scales. Instead, their body is covered with bony plates to protect them from predators. Their body orientation is vertical, not horizontal.

Seahorses don’t have pelvic fins, unlike most fish species. They rely on tiny dorsal fins that beat up to 30 times per second for swimming. These creatures have a specialized grasping tail that helps them cling to grass or corals. The seahorse is estimated to have diverged from other bony fish species about 100 million years ago during the Cretaceous period.

Male seahorse, not females, give birth to babies

These are the only known vertebrates on Earth that exhibit true male pregnancy. During the mating ritual, the female seahorse deposits as many as 1,500 eggs into the male’s brooding pouch. The male seahorse fertilizes the eggs internally and carries them in the pouch, providing safety, food and oxygen until the eggs hatch. The babies get no more parental care after the birth. The adults can start the mating process again almost immediately.

Biologists led by Byrappa Venkatesh of Singapore’s Institute of Molecular Cell Biology sequenced the genome of the Southeast Asian tiger tail seahorse that grows up to 10cm long. Though the analysis of the genome is still in early stages, scientists were able to find a few interesting genetic secrets behind the seahorses’ unique traits.

The saga of missing genes

For instance, a set of genes that code for tooth production in other animals had mutated and lost functionality in seahorses. It helps explain why these creatures don’t have teeth in their tube-shaped mouths. A gene that is responsible for egg hatching in other fish underwent duplication in the seahorse and assumed a new role, which led to the advent of male brooding pouch.

A gene responsible for the development of pelvic fins was also absent in the seahorse DNA. Byrappa Venkatesh said the seahorse protein and DNA evolved much faster than their cousins like sea dragons and pipe fish. Further analysis of the genetic sequence could offer more insights into their eccentricities.

Photo by oscar alexander