In ancient Greek mythology, it is said that Apollo, the god of sun and light, transformed himself into a dolphin then he brought the Cretans to Delphi where they built him a temple afterwards.
Dolphins are a symbol of affection and the love of life - therefore you will mostly find pictures with two dolphins close together. When thinking about getting a dolphin tattoo, it's a very good choice for a tattoo for a girl or young woman but you should decide first what you want to express with your tattoo. Depending on which culture, dolphins have different meanings. For the Celtic people, a dolphin symbolizes rejuvenation while to the Native Americans they symbolize kindness. A pair of dolphins means harmony to the Chinese. For sailors, it means guidance and they considered the dolphin as their patron. But many people see them as a symbol of good luck, and decide to get their good luck charm tattooed on their skin. Dolphin also teaches us that we are living in a world of tune with patterns and rhythm of nature. It also symbolizes breath of life, balance and community for some people. It can also be a symbol of freedom, trust, wisdom, harmony, innocence and purity of one's being.
For girls who wants a dolphin on their skin, if it is supposed to be the sign of affection which is very feminine then go for 2 dolphins. If you want it to be a sign of independence and freedom you are better off with only one dolphin. But no matter if you decide for one or two dolphins, they are a mighty sign of protection, joy and love which by all means is good to have.