This is a little background info on the wonderful dolphin
DOLPHIN AND PORPOISE
Dolphins are small members of the whale order, Cetacea. Although the terms dolphin and porpoise are sometimes used interchangeably to refer to any member of the group, biologists recognize three distinct families: the true porpoises, with six marine species; the river dolphins, with five freshwater species; and the true dolphins, with more than 30 marine species. The killer whales and pilot whales are closely related to the true dolphins and are included in the same family.
Although they are similar in appearance, a dolphin is distinguished from a porpoise by its long, sharp snout that is flattened like a beak; a porpoise has a short, blunt snout. The teeth of dolphins are cone-shaped while those of porpoises are flatter.
Dolphins and porpoises, often called simply "small whales," are mammals, not fishes, and are thus warm-blooded, keeping their body temperature nearly constant even when they are exposed to different environmental temperatures. The mothers provide milk for the young and nurse them for a year or more. Like other whales, dolphins have lungs and breathe through a single nostril called the blowhole located on top of the head. The blowhole is opened during their frequent trips to the surface to expel and inhale air. In contrast to some of the large whales, dolphins and porpoises have teeth, which they use to seize their food, consisting primarily of marine fishes and larger invertebrates, such as squid.
Dolphins and porpoises have two flippers, fins that serve as forelimbs, and an upright triangular fin on the back. The tail is horizontal to propel the animal in its lunges and dives not perpendicular like the tails of fishes. Dolphins and porpoises are noted for being graceful swimmers, arcing through long, slow curves that bring the blowhole to the surface of the water and then expose the back fin as the animal dips downward. At first glance, the high dorsal fin somewhat resembles that of a shark and has sometimes caused false alarms at beaches. Dolphins and porpoises have been clocked at sea traveling at speeds of more than 25 miles (40 kilometers) per hour.
The largest dolphins reach a length of about 15 feet (4.6 meters), but most species are 7 to 10 feet (2.1 to 3 meters) long. Porpoises are somewhat smaller. Dolphins and porpoises have smooth skin with a rubbery texture. Most species have color patterns that are some combination of black, white, and gray. Like other whales, they have an insulating layer of blubber beneath the skin.
Most dolphins and porpoises have declined in numbers during this century. Some species are hunted commercially, particularly in Asian marine waters. Many individuals of several species are accidentally drowned each year when they become entangled in fishing nets.
True dolphins belong to the family Delphinidae; true porpoises to the Phocoenidae; and river dolphins to the Platanistidae. All are in the toothed-whale suborder Odontoceti.
Dolphins and porpoises are noted for their intelligence and learning abilities. They have proved to be superb acrobats under certain conditions and can be trained to perform impressive tricks in oceanariums. Their social behavior and organization are among the most complex and advanced in the animal kingdom. Dolphins and porpoises exhibit an intricate communication and detection system in the form of underwater sonar that consists of high-pitched whistles and squeaks, some of which may be of ultrasonic frequency that is, above the range of human hearing. They are able to detect objects underwater by using "echolocation" in which the sounds are reflected off solid surfaces back to their sensitive ears. By means of echolocation they can recognize schools of fish or even smaller organisms such as shrimp. The time it takes for a reflected sound to return indicates how far away an object is from the animal.
Dolphins and porpoises also use sounds for communication among themselves as members of a school (also called herd or pod), which may consist of more than 1,000 individuals in some open-ocean species. Often an entire school will function as a unit to accomplish some objective, such as trapping fish.
Certain species of marine dolphins are the best known biologically because they survive well in captivity, allowing them to be more carefully observed. The bottle-nosed dolphin, whose scientific name is Tursiops truncatus, has been the most intensively studied because of its adaptability to salt-water holding tanks. It is a major participant in the acrobatic shows at oceanariums and is noted for its curiosity toward humans. Bottle-nosed dolphins, so called because of their long beaks, are found in all oceans of the world from the tropics to the temperate regions. They grow up to 12 feet (3.7 meters) long and may weigh more than 400 pounds (180 kilograms).
The common dolphin (Delphinus delphis) is also a species found worldwide in warm coastal waters and is a frequent inhabitant of the Mediterranean Sea and the Black Sea. Some other species are more restricted in their geographic range. For example, Peale's dolphin (Lagenorhynchus australis) is native to cold waters of the Atlantic and Pacific off the southern part of South America. Hector's dolphin (Cephalorhynchus hectori) is a small species reaching a length of only 5 feet (1.5 meters) and whose range is limited to the offshore waters of New Zealand.
Dolphins are relatively long-lived, with some individuals living more than 20 years. Most species do not begin to breed until ages of 5 to 8 or more. The female bears a single offspring, called a calf, after a gestation period of 8 to 11 months, depending on the species. As soon as the calf is born, the mother nudges it to the surface for its first breath of air.
The young stay with the mothers for at least one and sometimes as long as two years, while continuing to nurse. Most dolphins have their young in the warm months of the year.
The river dolphins are native to South America and southern Asia. The Ganges and Indus dolphins (genus Platanista) inhabit the large rivers of the Indian subcontinent: the Ganges, Brahmaputra, and Indus. The whitefin dolphin (Lipotes vexillifer), a bluish-gray animal with a white underside, inhabits the Yangtze River of China. The Amazon dolphin (Inia geoffrensis) is found in the Orinoco and Amazon Rivers.
River dolphins can be distinguished from ocean-dwelling dolphins by their smaller brains and more limited interactions with each other. Their eyes can detect light but do not form an image. Thus in murky river waters these dolphins must depend solely on sonar and echolocation abilities for finding food (mostly fishes and shrimp) and avoiding objects
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