There is love in the water at the New England Aquarium.
Eight months after the aquarium finished a $17 million renovation of its centerpiece Giant Ocean Tank, the fish inside have given their new home the ultimate stamp of approval: They have gotten frisky.
Right now, the aquarium is experiencing an unprecedented and sustained burst in courtship and mating behavior among the 100-plus species inside the tank. The aquarium’s head diver describes it as a “brothel.” When a visitor recently dropped a pencil into the tank, a filefish immediately swam up to it and tried to seduce it.
“We’ve seen these spikes through the years, but nothing like this,” said Dan , the assistant curator in charge of the Giant Ocean Tank, who estimates that 90 percent of the species inside are mating.
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The boom in mating is an incredible sign of the health of the new tank, a barometer to scientists that things inside are going very well.
“You need to have a lot of things in place before two fish are going to look at each other and say, ‘What do you think?’ ” said Steve Bailey, the curator of fishes. “Reproduction does not happen until a whole lot more important questions have been answered, like ‘Am I getting my butt kicked by other fish?’ ‘Is the water good?’ and ‘Am I getting enough food?’ ”
All over the tank, fish large and small can be seen guarding eggs, which means chasing off predators and trying their best to scare away the aquarium divers as they make their daily rounds. The defensive behavior is often the best way for the aquarium staff to know who has recently laid eggs since much of the “boinkulation,” as Bailey likes to call it, happens after lights out.
The spike in mating is attributed to a complex variety of factors, but the short answer is that the Caribbean coral reef inside the exhibit is a much more sophisticated ecosystem replication than its predecessor in the old tank. The new reef, which features three times the soft and hard coral features of its predecessor, has more places for fish to hide, set up territories, and partner up.
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“There’s a lot of romance in here,” Bailey said. “It’s like a soap opera.”
The aquarium has a successful track record of breeding particular species behind-the-scenes. They are masters at tricky jellyfish, which they supply to many other aquariums. And in small tanks in a hidden corridor outside public view, they have been breeding two species of African fish that have gone extinct in the wild.
But breeding has never been a priority for the Giant Ocean Tank, whose species are relatively common in the wild. The exhibit is not designed to create the very specific food web that is necessary for a microscopic egg to grow into a juvenile. For that to occur, eggs and larvae need to be removed from the giant tank and placed in smaller tanks, under very tricky-to-create conditions, if they’ll have any chance of survival.
But the mating boom has led the aquarium toward being a program that seeks to do that, because for the first time in the aquarium’s history, they have the space to.
As part of the massive renovation, the aquarium needed a place to store the species that had to be removed from the exhibit during the reconstruction, so they bought a massive warehouse in the Fore River Shipyard in Quincy and made it something of an ark to house those species. Now that those animals are back at the Central Wharf facility, they have space in Quincy to begin learning how to hatch them out.
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Harvesting eggs has become a regular part of morning rounds for the aquarium’s divers. On Thursday, Sean Marden, an aquarist in the Giant Ocean Tank, donned his scuba gear and lowered himself into the tank to look for new additions. Often, they’re easy to spot, like the purple streaks of tens of thousands of eggs laid by Sergeant Major fish on smooth surfaces.
But much of the time, the eggs are hidden in the sand, so they keep an eye on fish behavior and when they get a sense that a fish is trying to chase them out of a specific area, that’s the signal to start digging. A few days ago, divers gathered up a few square inches of sand that contained tens of thousands of Blue Chromis eggs, each one of them a victory for the tank.
“If we have animals that have the time and energy to reproduce,” Marden said, “we know that they’re happy.”
As Bailey watched Marden swim around in the tank, a pack of aquarium staff arrived carrying a large orange barrel containing an animal that had just been in for a check-up. For Bailey, it was the set-up for the perfect punch line.
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“That’s a moray!” he announced.
Billy Baker can be reached at billybaker@globe.com. Follow him on Twitter @billy_baker.