The whale shark, a massive inhabitant of the ocean, often sparks confusion due to its name. Despite the “whale” in its common name and enormous size, the whale shark is not a mammal. It is the largest known fish species currently alive, reaching lengths of up to 60 feet and weighing over 40,000 pounds.
Understanding Mammals and Fish
Mammals and fish are two distinct animal groups, each with defining biological characteristics. Mammals are warm-blooded, meaning they maintain a constant internal body temperature. They breathe air using lungs, give birth to live young, and nourish their offspring with milk produced by mammary glands. Mammals also possess hair or fur at some point in their lives.
Fish are cold-blooded, with their body temperature largely influenced by their surroundings. They breathe underwater by extracting oxygen through gills. Most fish reproduce by laying eggs, though some species give birth to live young without nursing them. Fish have fins for movement and possess scales or dermal denticles covering their skin, rather than hair or fur.
Why the Whale Shark is a Fish
The whale shark exhibits several characteristics that place it within the fish classification. Like all fish, whale sharks breathe using five large pairs of gills, which efficiently extract oxygen from the water as it passes through their specialized filter pads. This gill-based respiration sharply contrasts with the lung-based breathing seen in mammals.
Whale sharks are primarily ectothermic, or cold-blooded, meaning their body temperature generally aligns with the surrounding water temperature. While their large size provides some thermal inertia, slowing down changes in body temperature during deep dives into colder waters, they do not internally generate heat to maintain a constant body temperature like warm-blooded mammals.
Their reproductive strategy aligns with fish, as whale sharks are ovoviviparous. Eggs hatch inside the mother’s body, and live young emerge, but there is no direct placental connection or nursing with milk after birth.
The whale shark’s physical structure is characteristic of a fish. It possesses a cartilaginous skeleton, typical of sharks and rays, rather than the bony skeleton found in most fish or the combination of bone and cartilage in mammals. Their skin is covered in tiny, tooth-like structures called dermal denticles, which reduce drag and offer protection, instead of hair or fur. They also have multiple fins—two dorsal fins, pectoral fins, pelvic fins, and an anal fin—all adapted for aquatic movement.
The “Whale” in Whale Shark
The presence of “whale” in the animal’s name often leads to the misconception that it is a marine mammal. However, this part of its name is a descriptor for its immense size, which can rival that of some whale species.
Another reason for the “whale” designation stems from its feeding behavior. Like baleen whales, whale sharks are filter feeders, consuming vast quantities of plankton and small fish by straining them from the water. They open their broad mouths to take in water, which then passes over their gill rakers, trapping food particles. This shared feeding strategy and impressive size contribute to the common name, but they do not alter its biological classification as a fish.