First of its kind bright orange shark caught and released on Costa Rican coast

A bright orange nurse shark with white eyes has been caught and released off the coast of Costa Rica in what scientists say is the first documented case of the species showing a rare pigmentation condition.

The 2-metre-long shark, reeled in earlier this year by sports fishers near the village of Parismina, displayed xanthism, or xanthochroism, which increases yellow pigmentation in the skin, according to a study published on Thursday in the journal Marine Biodiversity, says Live Science.

"We could not believe what we had in front of our eyes," said Garvin Watson, a hotel owner who caught the shark and released it back into the Caribbean Sea after taking photographs. "That orange shark shining with the sunlight was something out of the ordinary."

The shark had total xanthism, with the anomalous pigmentation covering its whole body. Photo: Garvin Watson and Parismina Domus Dei. Parismina Limón Bar, Costa Rica.

Nurse sharks (Ginglymostoma cirratum) are usually yellow to grey-brown. While cases of albinism and unusual coloring have been noted, researchers said this is the first confirmed record of xanthism in the species. The animal also appeared to lack black irises, suggesting it may have been both albino and xanthic, a condition known as albino-xanthochromism, says Live Science.

"We were very surprised and excited when we saw the photos," said study lead author Marioxis Macías-Cuyare, a doctoral candidate at the Federal University of Rio Grande in Brazil.

Scientists believe xanthism is usually genetic, but stress, temperature or hormonal factors may also play a role. How the shark survived to adulthood despite its bright colouring, which would normally make it more visible to predators, remains unclear.

"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.