Scientists from around the world have joined forces to understand how the seahorse was able to evolve so differently from other fish. The study is currently analyzing the genome of a male Asian tiger tail seahorse to reveal why this fish does not swim horizontally and how did it evolve to make males to carry the pregnancy.

The study continues, but scientists have already published their findings on seahorses main unique features. The report was published today in the journal Nature and was possible thanks to international collaboration, including efforts from China and Germany.

Scientists are studying the evolution of seahorses. Photo credit: WaterFrame / Alamy Stock Photo / Science Mag
Scientists are studying the evolution of seahorses. Photo credit: WaterFrame / Alamy Stock Photo / Science Mag

This report shows the result of the first investigation on seahorses genetics and their evolutionary oddities. Seahorses are one of the strangest fish in the sea considering they look like little horses that swim vertically. The species lack a horizontal body orientation and instead of scales, they are covered with bony plates, an unusual feature on fish.

Another characteristic that makes seahorses a unique kind of fish is that they do not have pelvic fins. Instead, they have a dorsal fin that moves up to 30 times a second to let the creature move in coastal waters. They also have pectoral fins placed near the back of the head used for steering.

Seahorses do not have teeth, another peculiarity that scientists were eager to study. Rather, the small species has a tubular mouth which they used to suck in plankton and other tiny prey.

The Asian tiger tail seahorse: The most evolved seahorse

Researchers focus on the Asian tiger tail seahorse because it has had the fastest rate of molecular evolution among any fish whose genome has been studied. They can grow up to four inches (10 centimeters) long and have a yellow-and-black banded tail.

The study analyzed the species genetic basis by sequencing the genome of a male tiger tail seahorse. Its DNA was then compared to other bony fish species to see which genetics changes happened on the seahorse that other species did not experience.

Genes in charge to the formation of teeth in human beings and other species were mutated in seahorses and later lost functionality. This fact explains the fish tubular mouth.

When it comes to fins, the report reveals that seahorses do not have pelvic fins because the species do not have a gene involved in their development. The same gene is in charge of legs in the human DNA.

The research results show that the Asian tiger seahorse gene related to egg hatching underwent duplication. This change makes males assumed a new role that now makes them develop a pouch to fertilized the eggs of the female and carry the pregnancy.

How male seahorses get pregnant?

Female and male seahorses mating ritual can last up to four days. After the elaborate courting dance, the female can transfer up to 1,500 eggs to the male’s brooding pouch. The eggs are fertilized inside the pouch, where they also receive food and oxygen.

The pregnancy proceeds as one hosted by a female animal. The fetuses grow, and when they are ready, the male seahorse feels contractions. The seahorse has to push and eventually the embryos are giving birth to the ocean.

Source: Nature