Hmmm. The only dolphin fish I know of is the mahi mahi that is an open ocean dwelling species. I highly doubt this species would be able to be kept in an aquarium, so I'm guessing that's not the one you're referring to. Is there any way you could get a picture of this fish? Maybe that would jog my memory. I can't think of another dolphin fish. If all else fails, just ask the pet store how they take care of the ones they have. However, I should warn you that I have never come across a pet store employee (in my experience - no offense) that know anything about fishes. They claim to know, but I've had a few cases on the boards here that people have listened to the pet store people and their fish died. This is not to say you won't run into a few that might know what they are talking about.
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Phishie
"An ounce of prevention is worth a pound of cure."