How do you know when a male toadfish is looking for love? Easy—just listen for the grunts and boops.

Like some birds and frogs, toadfish sing to find a mate. In fact, if you didn’t know what to look for, the toadfish’s songs would probably be the only clue that that these smooth-skinned bottom-dwellers even exist.

“These are not the type of fish you see freely swimming around,” says Erica Staaterman, a bioacoustician at the U.S. Bureau of Ocean Energy Management. “They basically hide under rocks.”

However, if you were to drop a microphone under the waves on Panama’s Caribbean coast just after dark, you’d hear nothing but Bocon toadfish (Amphichthys cryptocentrus) trying to get fresh.

Staaterman learned this the hard way: She’d traveled to Central America to conduct an entirely different study on underwater sounds. But the toadfish had other plans. (Also read "Humming Fish Reveal Ancient Origin of Vocalization.")

“What we found in that study was like, ‘Holy cow, this one fish is drowning out everything else. What the hell is this thing?’” says Staaterman.

“It actually messed up our other data because it was so dominant in some of these ecosystems.”

Two-Note Toadfish

Confronted with an onslaught of toadfish a capella, Staaterman and her colleagues decided to study the boat-whistle-like noises of the Bocon toadfish. No one had ever recorded the Bocon, one of 70 toadfish species worldwide.

"As we were going through and seeing these calls in our analysis software, we started to notice these trends that each of these individual fish seemed to be composing their call differently,” says Staaterman. (Learn about more unusual animal sounds, like a bug that sings with its gentialia.)

Each male toadfish vibrated his swim bladder to make his own song, in other words, and each was composed of a combination of two basic notes—boops and grunts.

“Sometimes they would have these two little grunts they would do before the booping sound. Kind of like they’re clearing their throat,” says Staaterman, who led a recent study on the findings in the journal Environmental Biology of Fishes.

“Sometimes they would do one grunt and three boops, or two grunts and two boops. All of this seemed to vary across individuals,” she says.

What's more, the toadfish will grunt in the middle of a neighbor's song in what scientists believe is an attempt to jam up their rivals. Interestingly, Staaterman said males with more unique song patterns were less likely to suffer interruptions from their neighbors.

Allen Mensinger, a biologist at the University of Minnesota, Duluth, says the new study confirms what he’s seen in the oyster toadfish off Woods Hole, Massachusetts, though he notes his species, unlike the Bocon, stop calling when waters warm.

Space Oddity

Scientists have been studying toadfish since the 1800s, and the animals have helped us understand everything from insulin production to inner ear physiology to acoustic communication. Toadfish were even found to be the source of the so-called Sausalito Hum—a mysterious droning sound that boat owners in California reported hearing through the hulls of their vessels.

"We put them on the space shuttle and flew them in space on two different shuttle missions and they came back alive,” says Mensinger. (Read about a tiny creature that would likely survive the apocalypse.)

Even still, the creatures probably won’t be starring in animated movies anytime soon.

“They are so ugly,” says Staaterman. “They have these barbels that hang off their chin and these huge eyes, and their skin is mucousy and squishy.”

But this doesn’t make their acoustic behavior any less fascinating, says Staaterman. After all, a fish that relies on sound to find mates may not do so well in a world increasingly polluted with human-made noise.

“It’s a tough world out there for toadfish. You’ve got to sing as best as you can.”