Dolphins are viviparous, so they have nipples and nurse their young

Dolphins are aquatic mammals, and their nursing method has evolved a unique mechanism adapted to the underwater environment. Streamlined Body and Hidden Nipples To maintain a streamlined body that reduces drag while swimming in water, the nipples of female dolphins are normally hidden in **Mammary Slits** on the sides of their abdomen. The nipples only protrude slightly during nursing. Underwater Nursing Process Active Milk Ejection: Calves do not have flexible lips (they cannot suckle strongly like terrestrial mammals), so mother dolphins directly eject milk into the calf's mouth by contracting the muscles around their mammary glands. Tongue Forms a Seal: The calf curls its tongue into a tube to envelop the mother dolphin's nipple, and uses the serrated papillae on the edges of its tongue to create a tight seal, preventing seawater from mixing in or milk from dispersing into the water. Short and Frequent Feedings: Since calves need to surface frequently to breathe, each nursing session is usually very brief (ranging from a few seconds to tens of seconds), but is repeated dozens of times a day. High-Fat Milk Dolphin milk has a very high fat content (about 30% to 50%) and a thick, creamy, or milkshake-like consistency. The high-calorie milk allows calves to quickly build up a layer of blubber (cetacean fat) in a short period, providing not only warmth but also sufficient energy for swimming.