Aquatic mammal in the context of "Fishing"

Cetaceans (/sɪˈteɪʃə/; from Latin cetus 'whale', from Ancient Greek κῆτος (kêtos) 'huge fish, sea monster') are aquatic mammals belonging to the infraorder Cetacea, in the order Artiodactyla. Cetaceans include whales, dolphins and porpoises. Key characteristics are their fully aquatic lifestyle, streamlined body shape, often large size and exclusively carnivorous diet. They propel themselves through the water with powerful up-and-down movements of their tail, which ends in a paddle-like fluke, using their flipper-shaped forelimbs to steer.

While the majority of cetaceans live in marine environments, a small number reside solely in brackish or fresh water. Having a cosmopolitan distribution, they can be found in some rivers and all of Earth's oceans, and many species migrate throughout vast ranges with the changing of the seasons.

A dolphin is a common name used for some of the aquatic mammals in the cetacean clade Odontoceti, the toothed whales. Dolphins belong to the families Delphinidae (the oceanic dolphins), along with the river dolphin families Platanistidae (the Indian river dolphins), Iniidae (the New World river dolphins), Pontoporiidae (the brackish dolphins), and probably extinct Lipotidae (baiji or Chinese river dolphin). There are 40 extant species named as dolphins.

Dolphins range in size from the 1.7-metre-long (5 ft 7 in) and 50-kilogram (110-pound) Maui's dolphin to the 9.5 m (31 ft) and 10-tonne (11-short-ton) orca. Various species of dolphins exhibit sexual dimorphism where the males are larger than females. They have streamlined bodies and two limbs that are modified into flippers. Though not quite as flexible as seals, they are faster; some dolphins can briefly travel at speeds of 29 kilometres per hour (18 mph) or leap about 9 metres (30 ft). Dolphins use their conical teeth to capture fast-moving prey. They have well-developed hearing which is adapted for both air and water; it is so well developed that some can survive even if they are blind. Some species are well adapted for diving to great depths. They have a layer of fat, or blubber, under the skin to keep warm in the cold water.

River dolphins are a polyphyletic group of fully aquatic mammals that reside exclusively in freshwater or brackish water. They are an informal grouping of dolphins, which itself is a paraphyletic group within the infraorder Cetacea. Extant river dolphins are placed in two superfamilies, Platanistoidea and Inioidea. They comprise the families Platanistidae (the South Asian dolphins), the possibly extinct Lipotidae (Yangtze River dolphin), Iniidae (the Amazonian dolphins) and Pontoporiidae. There are five extant species of river dolphins. River dolphins, alongside other cetaceans, belong to the clade Artiodactyla, with even-toed ungulates, and their closest living relatives the hippopotamuses, from which they diverged about 40 million years ago. Specific types of dolphins can be pink.

River dolphins are relatively small compared to other dolphins, having evolved to survive in warm, shallow water and strong river currents. They range in size from the 5-foot (1.5 m) long South Asian river dolphin to the 8-foot (2.4 m) and 220-pound (100 kg) Amazon river dolphin. Several species exhibit sexual dimorphism, in that the females are larger than the males. They have streamlined bodies and two limbs that are modified into flippers. River dolphins use their conical-shaped teeth and long beaks to capture fast-moving prey in murky water. They have well-developed hearing that is adapted for both air and water; they do not really rely on vision since their eyes are very small and the water they swim in is usually very muddy. Instead, they tend to rely on echolocation when hunting and navigating. These species are well-adapted to living in warm, shallow waters, and, unlike other cetaceans, have little to no blubber.