There are 40 extant species named as dolphins. While dolphin attacks occur far less frequently than attacks by other sea animals, such as sharks, some scientists are worried about the careless programs of human-dolphin interaction.
Their skeletal anatomy allows them to be fast swimmers. Furthermore, the difficulty and expense of experimental work with large aquatic animals has so far prevented some tests and limited sample size and rigor in others. , In 1933, three hybrid dolphins beached off the Irish coast; they were hybrids between Risso's and bottlenose dolphins. Instead of sound passing through the outer ear to the middle ear, dolphins receive sound through the throat, from which it passes through a low-impedance fat-filled cavity to the inner ear. Other species kept in captivity are spotted dolphins, false killer whales and common dolphins, Commerson's dolphins, as well as rough-toothed dolphins, but all in much lower numbers than the bottlenose dolphin. Dolphins have been depicted in various cultures worldwide. , Dolphins' reproductive organs are located inside the body, with genital slits on the ventral (belly) side. Dolphins can live in either fresh or salt water.
If the animal then goes to the mirror in order to view the mark, it has exhibited strong evidence of self-awareness. However, dolphins are an informal group which is not self-contained taxonomically. In May 2005, a discovery in Australia found Indo-Pacific bottlenose dolphins (Tursiops aduncus) teaching their young to use tools. Loud underwater noises, such as those resulting from naval sonar use, live firing exercises, and certain offshore construction projects such as wind farms, may be harmful to dolphins, increasing stress, damaging hearing, and causing decompression sickness by forcing them to surface too quickly to escape the noise..
In captivity, a bottlenose and a rough-toothed dolphin produced hybrid offspring. Because their group members were spread out, this was done in order to continue traveling together. Our latest podcast episode features popular TED speaker Mara Mintzer. Research in this field has suggested that cetaceans, among others, possess self-awareness.
These whistles are used in order for dolphins to communicate with one another by identifying an individual. Dolphins are part of the toothed whales.Generally, they are among the smaller whales.Most live in salt water oceans, but some live in rivers – there are oceanic dolphins and river dolphins.Dolphins are from 1.5 metres (4.9 ft) to 4 metres (13 ft) long, but the largest dolphin, the killer whale (or orca), can be up to 8 metres (26 ft) long.. All dolphins live in groups called "pods".
 Reviews of this and other published dolphin-assisted therapy (DAT) studies have found important methodological flaws and have concluded that there is no compelling scientific evidence that DAT is a legitimate therapy or that it affords more than fleeting mood improvement..
Sleep stages earlier in sleep can occur simultaneously in both hemispheres.
 The gestation period varies with species; for the small Tucuxi dolphin, this period is around 11 to 12 months, while for the orca, the gestation period is around 17 months. , Queensland's shark culling program, which has killed roughly 50,000 sharks since 1962, has also killed thousands of dolphins as bycatch. Dolphins and other smaller cetaceans are also hunted in an activity known as dolphin drive hunting. Hybrids between common and bottlenose bred in captivity had an intermediate amount of teeth. Compared to many other species, however, dolphin behavior has been studied extensively, both in captivity and in the wild. The most widely recognized species are the common and bottlenose dolphins (Delphinus delphis and Tursiops truncatus, respectively).The bottlenose, characterized by a “built-in smile” formed by the curvature of its mouth, has become a familiar performer in oceanariums.
 There are no known cases of mercury poisoning as a result of consuming dolphin meat, though the government continues to monitor people in areas where dolphin meat consumption is high.  Research done on signature whistle usage by other dolphin species is relatively limited. The most vulnerable dolphins include the Ganges river dolphin (Platanista gangetica) and the Indus river dolphin (P. minor), which are classified as endangered species, and the Atlantic humpbacked dolphin (Sousa teuszii), which is classified as critically endangered. The dolphin is said to be among the creatures which heralded the goddess' descent from the heavens and her mount, the Makara, is sometimes depicted as a dolphin..
 In humans, these cells are involved in social conduct, emotions, judgment, and theory of mind. Since most of the brain is used for maintaining bodily functions, greater ratios of brain to body mass may increase the amount of brain mass available for more complex cognitive tasks.
Dolphins also seem to have been important to the Minoans, judging by artistic evidence from the ruined palace at Knossos. Dolphin echolocation clicks are amongst the loudest sounds made by marine animals.
For example, a 2005 study found dolphins an effective treatment for mild to moderate depression.  They showed dolphins real-time footage of themselves, recorded footage, and another dolphin. Their escape is prevented by closing off the route to the ocean with other boats or nets.
In Hindu mythology the Ganges river dolphin is associated with Ganga, the deity of the Ganges river. Dr. Andrew J.  Accidental by-catch in gill nets and incidental captures in antipredator nets that protect marine fish farms are common and pose a risk for mainly local dolphin populations. An auditory experience influences the whistle development of each dolphin. Information regarding current population levels and trends remains elusive for many dolphin species.
Dolphins live in the world’s seas and oceans and in some rivers too. , There is debate over the welfare of cetaceans in captivity, and often welfare can vary greatly dependent on the levels of care being provided at a particular facility.
As well as this, the eyes of a dolphin are placed on the sides of its head, so their vision consists of two fields, rather than a binocular view like humans have. These conical teeth are used to catch swift prey such as fish, squid or large mammals, such as seal. Dolphins have rather small, unidentifiable spouts. There are more than 40 species of dolphins, but the number keeps changing as science learns more about these marine mammals.Most dolphins are part of the Delphinidae family, which includes those living in the ocean, but some other species live in rivers and have a different taxonomic classification.
, Dolphin safe labels attempt to reassure consumers that fish and other marine products have been caught in a dolphin-friendly way.
The dolphins are netted only while fishermen are in pursuit of smaller tuna.  They have also been seen protecting swimmers from sharks by swimming circles around the swimmers or charging the sharks to make them go away.
Mothers of some species fast and nurse their young for a relatively long period of time. The term dolphin usually refers to the extant families Delphinidae (the oceanic dolphins), Platanistidae (the Indian river dolphins), Iniidae (the New World river dolphins), and Pontoporiidae (the brackish dolphins), and the extinct Lipotidae (baiji or Chinese river dolphin). For most of the smaller species of dolphins, only a few of the larger sharks, such as the bull shark, dusky shark, tiger shark and great white shark, are a potential risk, especially for calves. When cooked, dolphin meat is cut into bite-size cubes and then batter-fried or simmered in a miso sauce with vegetables.