Dolphin (the animal)  
 
  Dolphins is a family of whales that exist in all oceans of the world.

Just like other whales, dolphins give birth to one kid at a time. Some months after birth, it starts to eat solid food
and usually stays six years with the mother.

Dolphins live mostly from fish and squid.

Several species often jump out of the water to make acrobatic movements.
This is interpreted as play, but through the jumps they see seagulls and can thus identify possible places with food.

Dolphins are social animals with high intelligence, and live in groups.

In places with great access to food, up to 1000 individuals are sometimes gathered.
If the flock is attacked, the adult, healthy dolphins form a ring around the small, injured or old, so that
attacking animals do not approach them.

Dolphins communicate, among other things, through echolocation.
In their heads there is an organ for this and therefore the pan often looks like a bump (called melon).
New research shows that for instance the bottlenose dolphin uses whistling sounds to call individual individuals within a group.
Sounds are not distinguished by frequencies but by the sound sequence, likewise as a name in humans.

The eyesight is also very well developed and mainly adapted for underwater location, but is good even above the water surface.

Dolphins are usually between 1.40 and 4.00 meters long. The largest species, the killer whale, even reaches a length of ten meters.
The smallest species weighs around 50 kg, while the killer whale can be 9000 kg!

The dolphin's body shape provides so low flow resistance that it can reach 55 km / h (almost 30 knots).

They have the ability to dive 15 minutes to an impressive 300 meters depth*, but usually they only dive for a few minutes.
Dolphins are also known for swimming near ships to "ride" on the wave.
 
  * Only in the late 1950s was the Swedish marine industry able to supply submarines with a depth of more than 150 m.
 
  Special thanks to Wikipedia for the information on Dolphins and HMS Sälen (HMS Seal) of submarine class Hajen III