A first-of-its-kind bright orange shark with white eyes has been caught and released in the Caribbean, a new study reveals.
The nurse shark (Ginglymostoma cirratum) had a mysterious condition called xanthism, or xanthochroism, which increases yellow pigmentation in the skin. Researchers have recorded xanthism in several animals, but this is the first definitive case of a nurse shark with the trait. The shark also appears to have albinism, making it even more unusual.
Sports fishers discovered the shark by chance off the east coast of Costa Rica in 2024. Garvin Watson, owner of the Parismina Domus Dei hotel in the village of Parismina, reeled in the shark, which was around 6.6 feet (2 meters) long and swimming 120 feet (37 m) below the surface.
“We could not believe what we had in front of our eyes,” Watson told Live Science in an email.
“That orange shark shining with the sunlight was something out of the ordinary,” he said. “We did not know that it was going to be a discovery worldwide, recognized by all the biologists of the world.”
The fishers photographed the shark, then removed the hook from its mouth and released it back into the Caribbean Sea. Researchers described the event and its significance in a new study published Aug. 1 in the journal Marine Biodiversity.
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Scientists have documented xanthism in a variety of species, including frogs, birds and fish. While some animals are normally yellow and orange, these colors are more prominent in xanthic individuals of these species.
Nurse sharks are typically yellow to gray-brown. There have been occasional reports of unusual coloring in this species, including albinism — characterized by a complete lack of melanin pigmentation in the skin and iris — and potential xanthism, but a xanthic nurse shark had never been scientifically documented before now, according to the study.
“We were very surprised and excited when we saw the [xanthism] in the photos,” study lead author Marioxis Macías-Cuyare, a doctoral candidate in biological oceanography at the Federal University of Rio Grande in Brazil, told Live Science in an email.
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The researchers spoke with Watson and studied photos of the shark. They noted that the shark lacked the black irises typically seen in shark eyes, and concluded that it was likely albino as well as xanthic. A 2018 study documented this combined condition, known as albino-xanthochromism, in a ray species (Raja montagui) found in the Irish Sea.
Researchers are still studying the causes of abnormal pigmentation in sharks. Such conditions are typically associated with genetics, but factors such as environmental stress, elevated temperatures and hormonal imbalances may also contribute to different colors, according to the study.
Macías-Cuyare said that xanthism is usually genetic, but more research was needed to understand the conditions influencing the shark’s anomalous pigmentation.
The shark’s survival is also curious. Animals evolve to be specific colors to better survive in their environments, so being bright orange when the species isn’t meant to be would normally be a hindrance. In this case, the shark has made it to adulthood and doesn’t appear to have been held back by its unusual color.
“Many factors influence this, such as the environment, but everything remains speculative until the variables that could influence this genetic condition are tested,” Macías-Cuyare said.
