After more than a year in the making; after pumping in 750,000 litres of water; and after introducing more than 7,000 aquatic creatures from all over the world, Bristol's new Blue Reef Aquarium is about to open its doors.

The £4 million attraction, which has taken over the former Wildwalk/Imax building in Millennium Square, will welcome its first paying visitors on Friday.

As builders are busily putting the finishing touches to the attraction and staff are introducing fish to their new tanks, general manager Susie Unsworth agrees to give me a sneak preview of the site.

We are joined by aquatics expert Zahra d'Aronville, who has managed the extraordinary operation of putting the new aquarium together.

"We have 250 different species, ranging from a Giant Pacific Octopus to a tank full of piranhas, so it really has been quite an undertaking to get them all settled into their new home," Zahra explains, as we walk through the lobby, past the cafe and gift shop, and on into the start of the aquarium.

The main entrance has been created to look like the rusty hull of a sunken ship.

"The idea of the first part of the display is that you're walking into and through a shipwreck," Susie says. "It's a brilliant way of bringing the exhibit to life – I think the children will absolutely love it."

The sunken shipwreck display concentrates on native British species – everything from sharks and rays to cod, pollack, flat fish and lobsters.

As you wind your way through the shipwreck, and past the enormous centrepiece 260,000 litre tank, you also pass smaller displays, featuring creatures such as spider crabs, seahorses, cuttlefish and conger eels. The hi-tech lighting has been specially designed to imitate the natural cycle of the day and night, and even variations in weather, in order to make the tanks as close to the natural environment as possible.

"We have tried to use captive-bred creatures wherever possible," Zahra explains. "But where we have sourced stock from the wild, we have done so in a sustainable way, which is managed to actually help the natural populations."

Interpretation panels and interactive touch screens allow visitors to find out more about the fish and their situation in the wild.

Once through the sunken shipwreck, visitors will make their way into the first of the botanical garden areas – the large glass conservatories left over from the building's Wildwalk days.

The Wildwalk/Imax attraction closed in April 2007 after operators revealed it was losing £1.5m a year. The Imax cinema will now reopen, showing 3D nature films, as part of the aquarium experience.

"It was eerie when we first came in, because the place had been empty for a couple of years," Zahra says. "But for more than six months we just left the building contractors to get on with their work of transforming it into the place you see now.

"We only started introducing the first fish a couple of weeks ago."

The first botanical garden area is themed as a Mediterranean climate zone – something like a mini-Eden Project.

A climbing ramp runs up through the vegetation, eventually reaching the open top of the shipwreck tank.

It is surrounded by displays of octopus, starfish, anemones and the horrendously ugly (but actually rather likeable) wolfish.

But the highlight of this space is an impressive mural of the Floating Harbour, which takes up one entire wall.

It is the work of artist Greg Winter, whose day job as a special effects artist in the film industry has seen him make a name for himself on movies such as Batman Begins, Charlie and the Chocolate Factory, Robin Hood, Clash of the Titans II and the two most recent James Bond movies. The Bristol theme is continued out of the mural, with 3D recreations of parts of famous Bristol buildings incorporated into the walls. There's even a pair of Banksy-esque rats.

Visitors then move through a "laboratory area", where youngsters can get to touch some of the exhibits, including star fish, crabs and sea anemones.

They then move on to the tropical reef display – another enormous 205,000 litre, open-topped tank, with a bridge across the top and a walk-through tunnel beneath.

Themed around mangrove swamps, the tank is home to black tip reef sharks, zebra sharks, nurse sharks, leopard sharks, stingrays, horned sharks, humphead wrasse, pufferfish and thousands of shoaling reef fish.

Visitors then make their way downstairs, through the second of the glass-covered botanical garden zones. This one has an Amazonian theme, with a crashing waterfall, and a tank containing dozens of rescue turtles.

"All the turtles have been rescued from homes where they were unwanted pets," Zahra says. "After the success of the Teenage Mutant Ninja Turtles cartoons, lots of kids encouraged their parents to buy turtles, never realising how big they can grow. We hope this display will educate people against buying pets without fully looking into the reality of how much they can develop after a few years."

Another tank featuring clownfish is also attempting to hammer home this serious point.

"After the Finding Nemo movie, every child wanted a clownfish as a pet. Having them here at the aquarium will give us the chance to talk to children and their parents about how impractical the idea can be," Zahra says

Admission to the new aquarium is £13.50 for adults, £9.20 for children. A family ticket for two adults and two children will cost £43.40.

● The new aquarium will feature 40 displays, with more than 7,000 individual creatures and 250 different species in naturally-themed habitats.

● Visitors will get close to more than 15 species of shark and ray.

● The total volume of water in the aquarium is estimated to be 750,000 litres. Remarkably, the state-of-the-art filtering system processes all of this water once every hour.

● The shipwreck display alone features 260,000 litres of water, and a main viewing window of 3m x 2m.