While the term “black shark” is often used colloquially, no single, scientifically recognized shark species officially bears this name. The concept likely stems from naturally dark-colored shark species and the common naming of certain non-shark fish, leading to a misunderstanding that many “black sharks” are not true sharks.
The “Black Shark” Misconception
The term “black shark” frequently causes confusion, particularly within the aquarium trade, where several freshwater fish species are marketed under this name. For instance, the Black Sharkminnow (Labeo chrysophekadion) is a freshwater fish belonging to the carp family, not a shark. This species is native to Southeast Asian rivers and can grow quite large, and is known for its entirely black body and fins. Similarly, the Red-tailed Black Shark (Epalzeorhynchos bicolor), also a carp, is another popular aquarium fish distinguished by its deep black body and red-orange tail. Despite their shark-like appearance, these are not true sharks.
Naturally Dark-Colored Shark Species
Many shark species exhibit predominantly dark or black coloration as a natural adaptation to their environment. The Greenland Shark (Somniosus microcephalus), for example, has a large, heavy body that can range from pale creamy-gray to blackish-brown. These sharks inhabit the cold waters of the North Atlantic and Arctic Oceans, often at great depths.
Another deep-dwelling species, the Portuguese Dogfish (Centroscymnus coelolepis), is typically a uniform golden to black color. This species is found in continental slope and abyssal plain waters, making it the deepest-living shark known. Certain lanternsharks (Etmopterus species) are also uniformly dark, an adaptation that helps them blend into the low-light conditions of their deep-water habitats.
The Oceanic Whitetip Shark (Carcharhinus longimanus) can appear grayish-bronze to brown on its dorsal side. While the Great White Shark (Carcharodon carcharias) is known for its gray dorsal area and white underside, some individuals can display a very dark, almost black, gray-brown coloration. Mako sharks, such as the Longfin Mako (Isurus paucus), have dark blue to grayish-black backs. Larger specimens of Shortfin Mako sharks (Isurus oxyrinchus) also tend to exhibit darker pigmentation on their dorsal surfaces.
Understanding Melanism in Sharks
Melanism is a biological phenomenon characterized by an unusually high production and deposition of melanin, the dark pigment responsible for skin and eye color, resulting in a dark or entirely black appearance. While many shark species are naturally dark, true melanism refers to an individual within a species that is typically lighter in color but presents as unusually dark or completely black due to this genetic variation.
True melanism is a rare condition across many animal species, including sharks. A melanistic shark’s coloration would be significantly darker than its species’ typical range. Although dark coloration is advantageous for camouflage in deep or murky waters, a melanistic individual in a species normally found in brighter environments might face challenges. While reports of melanistic sharks are not common, the observation of unusually dark individuals, such as the “black mako” sightings, sometimes prompts speculation about this genetic variation.