Mahi-mahi, dorado, or dolphin fish: What's in a name?

Why do East Coast fishing anglers and captains call these spectacular fish dolphin?
In Hawaii, they are called mahi-mahi. From Panama to California, they are called dorado. Supposedly mahi means strong in Hawaiian, and dorado means "golden one" in Spanish, so I get that. But where do East Coasters come up with the term dolphin? I mean, isn't THIS a dolphin?
I've got nothing against the East Coast ( in fact, I grew up there), but whatsup with the term dolphin? Is there any linguistic basis for calling it a dolphin? I'd like to know the answer.

I do know some things about these fish, which I will call dorado from now on. Keep in mind I'm not a fishologist, these are just things I have picked up through my own experience, and from talking with hundreds of anglers and captains over the years.
Dorado grow extremely rapidly, and if I'm not mistaken a 5 year old dorado is an old one. The males have the pronounced Herman Munster-like foreheads, while the forehead of the female slopes back gently. Males get much bigger, and the world record, 88 pounds, was caught in Cabo within the last 20 years.

Providing you don't catch them on heavy tackle, they are in my opinion one of the most fun fish to catch, because they go ballistic in the air and do all types of crazy acrobatic leaps. They turn color in a flash, going from white to neon yellow, green, aqua, blue, and even purple all sometimes within the same jump.

For fishing photographers like me, they make very tricky subjects, because their leaps are so unpredictable and lightning quick. In fact, they are easier to photograph underwater because they are usually calmer in their own element. It's hard to get a decent shot of the fish above water with their true colors; here's one of the few I have. Thanks to my friend Captain Jeff Rogers for dealing with the feisty bugger!

Their beauty disappears instantaneously when they are unhappy ( as in, when they realize they are becoming dinner). They immediately turn greenish brown and so getting a photo of them happy is quite difficult. In addition, they go totally nutso in the cockpit, so many people simply stuff them right in an ice chest to avoid having the thing flip out- literally and figuratively!

Below is a recent cover shot of mine of a dorado that my friend caught in Nicaragua. I was visiting Lance Moss and his wife at their Surfari Lodge (think epic fishing meets dream surfing vacation) and there were plenty of them there. Jeff looks cool as a cucumber in the pic but I can guarantee you it was a real pain to hold this fish. Most people can't handle it and drop it, resulting in chaos.
I probably don't have to tell you that they are one of the tastiest eating fish around, but one thing you might not know is that they just might be one of the healthiest fish to eat. Why? Well, do a google search on mercury in fish. Last time I checked, they have a very low mercury count, and I'm pretty sure that's due to their short lifespan and diet.

Kayak fishing for dorado is one of my all time favorite fishing activities. When they hit your bait or lure, the reel screems like a dentist's drill and all those acrobatic leaps are now happening right next to you, often at eye level or higher!