CHARLESTON, S.C. ? Sport fishermen routinely head offshore to catch the popular, green-and-blue mahi-mahi, and it has long been a tasty favorite on restaurant menus.

But bringing this fish back alive and settling it into an aquarium is not so easily done.

The South Carolina Aquarium found that out. Two of the four mahi-mahi it introduced in August have died, although aquarium officials aren’t sure why.

“We called different places that tried to keep them already and what we got was, ‘Well, there are about 101 ways for them to kill themselves,”‘ said Steve Vogel, the aquarium’s curator.

The suspicion is the notoriously feisty fish, which can swim at speeds of up to 50 knots, slammed themselves to death on the sides of the tank. Vogel hopes changing tank lighting and putting curtains over some viewing windows at night will help keep the powerful fish contained.

“They are used to wide-open spaces,” Vogel said. “They are such fast swimmers. They are so powerful, and they have never seen a wall.”

That’s part of the reason it’s unusual for most aquariums to display the mahi-mahi, also known as dolphin (not to be confused with the mammals related to porpoises and whales).

South Carolina’s aquarium wanted to display the mahi-mahi to offer something new for visitors and because sport fishing is important to the coastal economy.

The challenges began with the offshore collecting trip.

“We went out every day for three weeks,” Vogel recalled. “We got four fish the most expensive fish you can possibly imagine, if you add up all the costs.”

Sometimes fish would strike but were dead on the hook. Those that survived the stress of being caught had to be anesthetized for the trip to shore. Back at the aquarium, there were new challenges.

The mahi-mahi which are now three feet long and consume almost 20 percent of their body weight a day were placed in a holding tank shallow enough so they could not jump out. A bubbling hose was run near the wall of the tank so the fish could become accustomed to seeing the edge.

“With most fishes, they eventually learn what their boundaries are. The hard part is getting them through that learning curve,” Vogel said.

The mahi-mahi were later transferred to the aquarium’s showpiece three-story ocean tank with hundreds of other fish.

“This was an experiment more than anything else. This is a deep tank with straight walls. We weren’t sure they would adjust,” Vogel said.

Two apparently did not adjust and were found dead a few weeks later.

One was found at the bottom of the tank with part of its tail missing. It may have hit the side and, then stunned, become prey for other fish.

A second was found the next day, its stomach ruptured. It might have hit the wall or another fish, Vogel said.

Lighting was changed to give more of a moonlight effect and reduce the impression of being able to swim into infinity through a large viewing window. Curtains also are now closed on two of the tank’s smaller viewing windows.

There likely will be another trip offshore next summer to replace the dead fish.

“We’ll definitely try again,” Vogel said, “unless we determine flat out that these guys died from the impact with the walls something we can’t change.”