Rare Nurse Shark Puzzles Researchers in Costa Rica

During a tourist fishing expedition in Costa Rica, an unexpected encounter caught scientists’ attention: a nurse shark measuring nearly two meters long with extremely unusual genetic traits. The animal displayed a striking orange coloration caused by xanthism, and also showed signs of albinism, revealed by its completely white eyes.

The sighting, recorded in August last year by the company Parismina Domus Dei, recently gained new attention after the publication of a study by the Federal University of Rio Grande. According to the research, xanthism is a rare genetic condition that produces an excess of yellow or golden pigments, previously identified in certain birds, reptiles, and bony fish — but never before in sharks or other cartilaginous fish.

For specialists, the discovery raises important questions: is this simply an isolated case, or could it be evidence of more frequent mutations within the local population?

Normally, animals with xanthism face greater survival challenges, since the bright coloration makes them more visible to both predators and prey. However, the fact that this shark reached nearly two meters suggests that, so far, the condition has not compromised its life.

The situation becomes even more extraordinary due to the presence of albinism — a condition characterized by the absence of melanin, which can lead to pale skin, unpigmented eyes, and greater sensitivity to sunlight. In the recorded images, the shark’s white eyes clearly confirm this rare trait.

Under normal circumstances, adult nurse sharks have a brown coloration that helps them blend into reefs and sandy bottoms. The vibrant orange hue, in theory, would make hunting and protection more difficult. Yet this specimen seems to have overcome such obstacles, leaving scientists intrigued about possible adaptive advantages behind these two unique genetic conditions.

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