Coryphaena hippurus.........technically, they are now classified as "Dolphinfish".
On the east coast, most people call them "dolphin".
West coasters call them "Dorado".
Hawaiians call them "Mahi Mahi".
As they became more popular nationwide as table fare, most people came to know them as "Mahi Mahi"..........certainly more glamorous than "dolphin"........and I suppose the wait staff would get tired of explaining, "NO....you are not eating a mammal!!!".
The last few places I fished were in Florida and Long Island..........everyone there called them "Mahi".....so I guess this is becoming the universal term; although I still call them "dolphin".