First record of severe hypopigmentation in a tiger shark Galeocerdo cuvier from the southwestern Atlantic Ocean
This study documents the first record of severe hypopigmentation, likely leucism, in a tiger shark (*Galeocerdo cuvier*) captured in the southwestern Atlantic Ocean, highlighting the value of fishery-dependent observations for identifying rare phenotypic traits in marine megafauna.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of a preprint that has not been peer-reviewed. It is not medical advice. Do not make health decisions based on this content. Read full disclaimer
The ocean is a place where appearance often determines survival. For many marine animals, the ability to blend into their surroundings is a matter of life and death. This is achieved through pigmentation, the biological process that gives skin, scales, or feathers their color. Sometimes, this process goes awry due to genetic or environmental factors, resulting in animals that look strikingly different from their peers. These rare individuals might be completely white, lacking the dark spots or stripes that usually help them hide. While scientists have documented such color variations in many land animals, finding them in the open ocean is difficult because the deep sea is vast and hard to watch. When researchers do spot a shark or a ray with unusual coloring, it offers a rare glimpse into the hidden diversity of marine life and raises questions about how these animals survive when their natural camouflage fails.
In the coastal waters of southeastern Brazil, a team of researchers recently documented a remarkable instance of this phenomenon. They recorded the first known case of severe hypopigmentation—a condition where an animal loses most of its natural color—in a tiger shark. The shark was caught in May 2022 by an industrial fishing vessel operating in the Lagamar marine complex, an area recognized as a critical habitat for sharks and rays. The specimen was a young male, and while its head had been removed before it was brought to shore, the rest of its body told a clear story. Instead of the dark, striped pattern typical of juvenile tiger sharks, which usually helps them hide among the rocks and sand of shallow coastal waters, this shark was almost entirely white.
The researchers examined the animal carefully, noting that it retained only very faint, ghostly traces of the dark markings usually found on its back. These remnants were so light they appeared as diffuse grey smudges rather than the sharp stripes seen in healthy sharks. Because the head was missing, the scientists could not check the eyes to confirm if the animal was completely white or if it had some color there, a detail that would distinguish between different types of color loss. Following standard guidelines for classifying such conditions, the team conservatively identified the shark as suffering from severe hypopigmentation consistent with leucism. This is a condition where an animal produces less pigment than normal, resulting in a pale or white appearance, but unlike albinism, it does not necessarily affect the eyes. The shark showed no signs of injury, disease, or scarring that might have caused the color loss, suggesting the condition was inherent to the animal.
The discovery is significant not just for the rarity of the shark's appearance, but for where it was found. The Lagamar region is a complex mosaic of islands, mangrove forests, and sandy bottoms, a place where juvenile tiger sharks usually grow up. In such a busy and varied environment, the dark stripes of a young tiger shark act as a disguise, breaking up the animal's outline so predators and prey cannot easily spot it. The loss of this pattern likely made the white shark much more visible than its normally colored cousins. While the researchers cannot say for certain how this affected the shark's life, the fact that it was caught suggests it was still alive and moving through these waters, despite the potential disadvantage of being so easy to see.
This record adds a new piece to the puzzle of shark biology. Although reports of color abnormalities in sharks have increased as more people document marine life, cases involving tiger sharks remain very rare. Most previous accounts of unusual tiger sharks come from other parts of the world, such as the eastern Pacific or the Maldives, making this the first documented case from the southwestern Atlantic. The finding highlights the value of working with local fishers, who are often the first to encounter these unusual animals. By sharing their observations, they help scientists build a more complete picture of the ocean's inhabitants, proving that even in a world as vast as the sea, the most extraordinary creatures can still be found in the most unexpected places.
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