If you are fascinated by sharks, you might want to visit the Tennessee Aquarium soon. They have recently hatched a 𝑏𝑎𝑏𝑦 shark that glows in the dark!

A recently hatched swell shark exhibits biofluorescence. Image credit: Tennessee Aquarium

Yes, you read that right. This amazing creature is a swell shark, a species that lives in the Pacific Ocean and has a unique adaptation to see and communicate with other sharks in the deep sea.

A swell shark (Cephaloscyllium ventriosum) is a type of catshark that can grow up to three feet long. It has a brown body with dark and light spots that help it blend in with its surroundings. It feeds on fish, crustaceans and mollusks, and it can live up to 20 years.

The swell shark gets its name from its ability to inflate its stomach with water or air when threatened. This makes it harder for predators to bite or pull it out of its hiding place. It also makes a loud barking sound when it does this, which may scare off some attackers.

Even more interestingly, this mottle-patterned shark has developed a novel way to see its fellow species members in the cold, dark depths off the Pacific coastline from California to Mexico, which earned it the nickname “glow shark”.

“We call them that because they biofluoresce — they don’t make their own light, but they reflect light in a fluorescent manner,” says Senior Aquarist Kyle McPheeters, who first spotted the four-inch youngster.

“In the deeper parts of the ocean where they live, only the blue light is able to penetrate, so they are seeing in a blue light, but their eyes have a bit of a yellow lens on them,” McPheeters adds. “If you were to dive down to see them, they would look brown and would blend in really well in the dim light, but to each other, they would look like they were glowing.”

The swell shark absorbs blue light, which is the only color that reaches the deep ocean, and emits green light. To us, this may not seem very impressive, but to other swell sharks, it is a dazzling display. That’s because their eyes have a yellow filter that blocks out other colors and makes them see only green.

Scientists think that biofluorescence helps swell sharks find each other in the dark and possibly attract mates. They have noticed that male and female swell sharks have different patterns of glowing spots, which may indicate their gender and readiness to mate.

The Tennessee Aquarium has been keeping two adult swell sharks off-exhibit for a couple of years. They were surprised to find a 𝑏𝑎𝑏𝑦 swell shark swimming with them in August 2023. This was the first time they had successfully hatched an egg from this species.

An aquarist from the Tennessee Aquarium uses a light to illuminate the egg case of a swell shark. Referred to as “candling,” this technique enables caregivers to assess the developmental stage of the shark pups. Image credit: Tennessee Aquarium

The 𝑏𝑎𝑏𝑦 swell shark was about four inches long when it hatched, and it will take several years to reach its full size. The aquarium staff can see its glow by shining a blue light on it and wearing yellow glasses. They are monitoring its growth and health, and they hope to learn more about this fascinating species.

Sources: 1, 2, 3