It’s true that world music is more popular today than ever, and that more and more artists are creating increasingly unique hybrids by casting an ever-widening net—and reeling in ever-more disparate cultures and styles.

But having said that, you’ve still never heard a group that sounds like The Fishtank Ensemble. While critics generally refer to their polyglot as “cross-pollinated gypsy music,” that doesn’t nearly cover it. Their swirling, exotic, unpredictable music combines and re-combines such styles as Romanian, Gypsy jazz, Flamenco, Balkan, Turkish, the Tango - and even rockabilly.

And, mostly, they come by these styles naturally. Violninist Fabrice Martinez is French-born, but he spent many years wandering throughout Europe -- Italy, Hungary, Slovenia Romania, etc. -- soaking up those styles. And bassist Djordje Stijepovic is Serbian, but he was drawn early on to American rockabilly, and as a teen became one of the best slap-bass players on the music scene - playing Balkan music as well as rockabilly.

Guitarist Doug “Douje” Smolens was born in Guadalajara but grew up in California, and was part of the L.A. rock scene, playing drums and hanging out with Billy Idol and Slash. But one day, the sound of flamenco guitar caught his ear, and he traveled to Spain to learn from Gitano flamenco masters in the caves of Grenada.

Singer and violinist Ursula Knudson is American-born—a native of Sacramento—and was a classically trained opera singer, but her own wandering spirit lured her to Italy, where she sang opera on the streets, and where she discovered a love of Gypsy music.

“After all those classical-music lessons, it took me a few years to play around with my voice, to loosen up and just go with the emotion of the song, instead of thinking about maintaining my technique and my breathing,” says Knudson, who joins her bandmates for a show at The Ark on Thursday. “And three albums in, I’m still exploring the nooks and crannies of my voice, and of these songs.

“Gypsy music is very passionate music, and we have a couple of members who are much better versed in it than I—their travels took them to play music with Roma people and learn from them, so they have an inherent love of the music and deep respect for it,” says Knudson by phone from the band’s tour van, rolling along a Massachusetts highway. “But we don’t claim to be experts in Gypsy music, specifically, because we pull on so many other styles. We don’t play it the way the masters play it, we play our own hybridized version of it.”

Stijepovic’s rockabilly-style slap-bass work gives the music a pulse that, frankly, one doesn’t usually hear in Eastern-European folk-music hybrids. And, that pulse also brings an “attitude” to the music.

“It really pumps up the energy more,” says Knudson of Stijepovic’s swaggering bass lines. “It’s for people who want to dance and have a good time, and that deep low beat is like the thump of the heart. Without him, I think people would tend to just sit and listen to us more, but when Djordje starts in with the rockabilly style, it becomes more of a party.”

Not that Fishtank’s repertoire doesn’t include songs that are more nuanced and yearning, and more suitable for “sitting and listening.” Several of their tunes are heart-rending, and with her operatic training, Knudson is able to pull every bit of emotion out of those songs. She has other vocal influences, like Sarah Vaughan and Billie Holiday, whose inspiration she taps into when the need arises.

“I’m a parrot,” she jokes. “I have a knack for imitating other singers, so I draw on that, which can be fun, since this style of music we play can be a lot of fun. And it’s even more fun when I don’t know what it’s supposed to sound like, since we’re combining so many styles to come up with ‘our sound’ on a respective song.”

The group’s current disc, released in May, is “Woman in Sin,” and represents a bit of a change for the band. For starters, on their first two discs, Fishtank was a sextet, and this is their first effort as a quartet.

“So, we really wanted this album to represent who we are now, to present ourselves to the world as a quartet,” says Knudson. “And I find we’re actually able to do more as a quartet than we could do as a sextet. We did have guest musicians play on this album—we like to have a guest percussionist or brass players—but, before, with six instruments, we didn’t have as much flexibility in terms of what kind of music we could play. Plus, having two more people made it harder to tour sometimes.”

On “Woman in Sin,” the group decided to add even more cultural influences to the mix. “When we started out, on our first album, we played a lot of Romanian music, but I feel us heading eastward, more toward Turkey,” she says. “We have more Serbian material on this record, and a Kurdish song—but we also have a French song as well.”

Knudson and violinist Martinez are more than just bandmates. They’re also husband and wife. They met at a carnival in Venice several years ago, and were married 18 months later.

Working with one’s spouse can be a challenge in any profession, because the other spouse is “always around.” But it’s even more of a challenge when you’re a traveling musician, and spend much of your time cooped up in a van together, with two other bandmates.

“Plus, we tour with our 5-year-old son,” says Knudson with a laugh. “Yes, there are those challenges, it is better than the alternative - because if only one of us was in a touring band, we’d never get to see each other, because one of us would be on the road all the time.

“I think we do pretty well,” she says, before adding, with another laugh, “but the experience does teach you a certain amount of self-control.”

Kevin Ransom, a free-lance writer who covers music for AnnArbor.com, can be reached at KevinRansom10@aol.com.