Ryan Hunter-Reay slipped a mood ring on his finger one morning this week and looked at its color-coded diagnosis.

“Calm,” he reported.

The IndyCar driver tried on a second ring in the National Aquarium’s gift shop. The same cool blue result greeted him.

“I am so calm right now, it’s ridiculous,” he decided.

He was joking, but Hunter-Reay had just spent the better part of an hour explaining how marine life is a calming force for him, a relaxing distraction from piloting his Andretti Autosport ride better than 200 mph on ovals and road courses around the hemisphere.

It’s why he spends his offseason deep-sea fishing, and spear fishing, and exploring ocean wrecks. It’s why one of his favorite cardio workouts is a half-mile swim in the ocean near his Fort Lauderdale home, and why he works on his breathing by free diving. It’s why he has a 210-gallon custom-built saltwater aquarium in his home, and it’s why we decided to skip a formal interview in favor of a trip to the National Aquarium in the basement of the Department of Commerce.

“They’re beautiful fish,” Hunter-Reay told me at one point, as we stared at a tank of lionfish. “But they’re like rats.”

He went on to discuss their invasive traits, their venomous spines and their voracious appetites. We stared some more.

“Pretty cool-looking fish, though,” he added.

Hunter-Reay said he’s been fascinated by marine life since his parents plopped him in front of a tank when he was a child; he’s already passed on that fascination to his 5-month-old son Ryden, who “loves every bit of” their home aquarium and “lights up in front of it.”

When the driver was out of a ride in 2006 and “had time on my hands,” he created an extensive coral aquarium inside his California home. That was a casualty of his move to Florida, but the CEO of Living Color Aquariums — an open-wheel racing fan — arranged for Hunter-Reay’s current setup, which includes a puffer fish, yellow tangs, clownfish, and other treasures.

His driving career, of course, has also traveled quite a distance since 2006. The 32-year-old won the IndyCar championship last season — the first American to do so since Sam Hornish Jr. in 2006 — already has a win this season, and will start seventh in Sunday’s Indianapolis 500. He’s faced countless questions about whether he’d rather claim another series title or a Memorial Day weekend victory, and he has no doubts.

“Winning the championship has a certain meaning to it, but the Indy 500 is the biggest race in the world,” he said as we strolled past salamanders and turtles. “It’s a life-changer. It’s a career-changer. Now that I’ve already won a championship, I’d much rather have a 500 win.”

He completed about 500 practice laps in the last week to help prepare for the race, before coming to the District for a quick round of media appearances. And while he said the morning of the race brings a surge of adrenaline and butterflies, he also said he can’t enter that day “jacked up” like a football player.

“You just zone out,” he said. “You’re amped up, you’re ready to go, but if you get too tense, if your energy level is too high, then your brain isn’t working 110 percent. You make your best decisions in that zone between being on-edge and being calm and collected. It’s critical to get in that zone.”

Similarly, he said, his many encounters with marine life bring a balance to his life, countering the frenetic pace of racing with something altogether different.

“As soon as I get under water, I feel a reset,” he said. “That can turn the switch off for a couple of days, as hectic and as pressure-packed as racing is.”

This, though, is the biggest week of the year for IndyCar drivers, which means there’s not much time for communing with the fishes and “entering their element,” as he puts it. Which brings us back to those mood rings.

“Get one of those on Friday afternoon,” joked Hunter-Reay’s press assistant, “and see what it says then.”