National Aquarium, in Baltimore, has overhauled what once was a drab, leaky, concrete tank of mostly stingrays, adding 1,000 animals and 3,000 hand-sculpted coral replicas to create a colorful and massive new centerpiece exhibit.The exhibit had always been popular but became dated, and it is now teeming with new life after the $12.5 million renovation. The tank now includes 65 different animal species, including a beloved 555-pound, three-legged green sea turtle named Calypso.Last week, the aquarium added 20 new blacktip reef sharks from Australia to help complete an ecosystem that replicates endangered Indo-Pacific reefs. Divers carefully placed each shark in the 260,000-gallon exhibit one by one over several hours last Monday and Tuesday. Almost immediately, the sharks began swimming together as a school in their new home.Rather than eat all of the exhibit's smaller fish, however, these sharks have been trained over the past year to eat a variety of seafoods from animal keepers on schedules and at certain feeding locations, said senior aquarist Ashleigh Clews. The sharks look small now but will eventually grow to about 6 feet long.Curator Jack Cover said the aquarium set out to take its visitors on a journey to a place like the Great Barrier Reef to showcase the biodiversity that coral reefs support. So they created an exhibit to show what a healthy reef looks like to help inspire conservation of such ecosystems."All these things link together to form this aquatic community. Coral reefs really represent sort of the big cities of the ocean," Cover said. "We have a cave area, we have a terraced coral area, we have sand flats. So many species will really go to those different areas. It's almost like a city with different neighborhoods."Along with the smaller fish, the blacktip reef sharks are an essential part of a reef ecosystem in the wild, Clews said, by keeping fish populations in check and by removing sick and injured fish. As they trained for more than a year, Clews developed a bond with the animals after diving with them and interacting with them to prepare them for the exhibit. "They're shallow-water sharks, usually hanging out in the reefs," she said. "They're beautiful animals."Still, sharks are often misunderstood as ever-hungry, man-eating predators -- notions the aquarium would like to change, Cover said. And sharks are hunted for their fins, meat and skins."People really have a completely wrong picture of what they do and that they have a role in the health of a healthy ecosystem like a reef," he said. "We wanted to basically show it and then tell [visitors] that if the sharks are removed, the reef is going to suffer."Visitors can get a sense of what it's like to be at sea level, as well as to gaze down on the tank full of fish from a bird's-eye view. Concrete walls have been replaced with glass walls to open up the exhibit space.One major addition is a large glass-enclosed underwater viewing area that juts into the coral habitat to replace what had been two small portals. Now visitors can see tiny blue and orange fish that feed and hide in the coral and have an up-close look at sharks and the giant sea turtle."It's like you're entering their world," Cover said. "It will look very different."The result is a colorful, lively centerpiece for one of Baltimore's top attractions, which draws about 1.5 million visitors each year with its companion aquarium in Washington. The renovation was funded with a combination of government funds and donor contributions. The aquarium will celebrate the exhibit's grand opening Aug. 8.Soon it will also add fish from the aquarium's Washington location, which is closing because of renovations at its home in the Department of Commerce.