This gregarious whale can be up to 5m (16 ft) long, larger than all but the largest dolphins but smaller than most other toothed whales. Males are generally larger than the female - males can weigh 1.5 tons and females about one ton. Newly-born Beluga are about 1.5m long and weigh 80kg. This whale is unmistakable when adult: it is all white and has a dorsal ridge rather than a fin. The head is also unlike that of any other cetacean - its melon is extremely bulbous and even malleable. The beluga is able to change the shape of its melon by blowing air around its sinuses. Again unlike many whales, the vertebrae in the neck are not fused together, allowing the animal flexibility to turn its head laterally.
The absence of the dorsal fin is reflected in the genus name of the species - apterus is the Latin for "finless". The evolutionary preference for a dorsal ridge in favor of a fin is believed by scientists to be adaption to under-ice conditions, or possibly as a way of preserving heat.
The body of the Beluga is rotund, particularly when well-fed, which tapers smoothly to both the head and tail. The tail fin grows and becomes increasingly ornately curved as the animal ages. The flippers are broad and short - making them almost square-shaped.
Males become sexually mature at eight years, females at five. Females give birth to a single calf in the spring after a gestation period of fifteen months. Young Belugas are uniformly dark grey in colour. The grey steadily lightens as they grow up - reaching their distinctive pure white colour by the age of seven in females and nine in males. The nursing periods is about two years. The mating process is not properly understood. Mating certainly does occur during the winter or early spring, when the animals are still in their winter grounds or have begun their migration. However mating does occur at other times too; leaving open the possiblity of delayed implantation. Belugas live for up to forty years.