Dauphin, pronounced "dolphin," is the title of the heir apparent of the French throne and of an island off the coast of Alabama, but it is not a fish. Dauphin fish is likely a misspelling of the homonym "dolphin fish," a colloquial name for Mahimahi.
Dolphin fish, also known as Dorado, are tropical fish found worldwide. Dolphin fish are often caught while big-game fishing as they are blue marlin's favored prey. Dolphin fish swim in large schools and refuse to leave hooked fish behind, so a common fishing tactic is to leave a hooked fish in the water and throw bait to other fish that stay with their comrade.