A shark with an orange appearance caused by a rare skin condition was caught off Costa Rica. Researchers said the coloring resulted from xanthism, a pigmentation disorder marked by an excess of yellow tones, which had not been documented in cartilaginous fish in the Caribbean.
A group of friends on a sport fishing trip near Tortuguero National Park hooked the animal after seeing its fin break the surface several times. When they brought it in, they saw a bright orange nurse shark with white eyes measuring about 198 centimeters. “It looked like an alien,” one of the fishermen said.
The shark was identified as a nurse shark with intense yellow-orange pigmentation and white eyes, suggesting albino-xanthochromism. Nurse sharks are usually light to dark brown, a coloring that helps them blend into reefs and rocky habitats.
Bright orange skin and pale eyes can make a shark more visible to predators and prey. Researchers from the Federal University of Rio Grande said the animal’s size indicated it reached adulthood, suggesting the coloration did not prevent survival to maturity.
Scientists, including a doctoral student from the Federal University of Rio Grande, began examining the genetic basis of the shark’s coloration and whether environmental factors played a role. They also asked if the case was isolated or part of a wider trend in the local population.
What is Xanthism?
Xanthism is typically caused by a genetic mutation, though diet can also influence pigmentation. The opposite condition, axanthism, is marked by a lack of yellow pigment. Albinism stems from the absence of melanin, producing pale skin and white or red eyes, and can increase sensitivity to sunlight. Both conditions can reduce camouflage, which may lower survival rates in the wild.
Xanthism has produced vivid yellow and orange morphs in freshwater fish such as guppies, cichlids, and goldfish. Certain birds, including parrots and canaries, have shown golden plumage, and there have been occasional reports of unusually yellow snakes and lizards. Researchers noted that the condition remained rare across marine species in the region.
Nurse sharks can reach up to 4.30 meters and are generally harmless to humans unless threatened. Unlike many sharks that must swim to breathe, nurse sharks use a buccal pump to draw water over their gills while resting.