The concrete floor of what will be Toronto’s biggest fish tank, in the city’s first tourist attraction in two decades, is down. Now we wait for sharks.

Construction crews at the Ripley’s Aquarium of Canada site south of the CN Tower poured the massive, 40-centimetre-thick pad on Saturday. Finishers worked until the wee hours of Sunday, then left the slab to cure for two weeks.

“We did it in one continuous pour so there aren’t any ‘cold joints’,” that could make a leaky seam, said Joe Choromanski, Ripley’s vice-president of husbandry, in an interview from the company’s Orlando headquarters.

“It’s huge — it’s a huge exhibit,” he said of the 2.8-million-litre shark tank, the centerpiece of the $130 million aquarium (including $11 million from the Ontario government) set to open in summer 2013.

Construction is now about one-fifth complete, Choromanski said, adding that this winter’s warm temperatures helped keep work on schedule.

Visitors will glide through the tank on a moving sidewalk, looking up and around at creatures including four-metre-long sand tiger sharks, stingrays the size of area rugs and otherworldly sawfish.

In total, various tanks will be home to more than 13,500 marine and freshwater fish in 5.7 million litres of carefully formulated solution that will start as Toronto tap water.

Ripley’s, owned by B.C. billionaire Jim Pattison, operates aquariums in Gatlinburg, Tenn. , and Myrtle Beach, S.C.

Choromanski said Ripley’s has a special concrete formula that includes fly ash, a byproduct of burning coal, to make the concrete extra waterproof.

And because sharks have a highly developed sensitivity to electrical fields that leads them to distant prey, no wiring is laid under the tank’s thick bottom slab.

“It costs a lot of money to reroute those conduits all the way around the perimeter of the building,” said Choromanski, “but we found over the years that even a tiny bit of stray voltage will drive sharks crazy.

“It was a learning curve for our (Toronto) contractors, who couldn’t understand why we go to the trouble of taking the long way around.”

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The fish will start arriving in spring 2013.