Let’s Jaw about Jawfish

What do we humans do with our jaws? Bite, chew, talk and… that’s about it. Pitiful, right? Aside from a few visits to the dentist and the odd plastic surgeon, we have a lamentable lack of imagination when it comes to finding exciting projects for the lower portion of our faces.


Jawfish are some 80 species within the Opistognathidae family, found in warm, marine environments across most of the world. The biggest of them all is the Giant Jawfish (Opistognathus rhomaleus) at 50 cm (18 in) long. Most of the others are less than 10 cm (4 in) in length.

Giant Jawfish (Opistognathus rhomaleus)
Giant Jawfish (Opistognathus rhomaleus)

They’re all rather slender in body shape. Not to the extent of a snake or eel, but a lot like a blenny. Blennies are fish who love a good hole in the ground. A nice little cave to nestle in. Often the only thing you can see of them is a head poking out of a rocky crevice or abandoned tubeworm burrow. Sometimes these caverns are situated in sponges, right in the midst of the hustle and bustle of coral reefs.

Jawfish are more suburban in their habits. They tend not to live in the middle of reefs, but the outskirts. The land here is more flat and featureless. There aren’t so many rocks, corals, sponges or ready-made burrows. Thus, in order to disappear, they must dig.

And that’s exactly what they do!

Jawfish are masters of civil engineering. Especially tunnels. They don’t do bridges. Oh, and only tunnels that stop in a dead end. So… caves. They’re really good at making caves to live in. It’s the civil engineering of our ancient ancestors.

They dig by filling their mouths with sand and spit it out elsewhere, slowly creating a tunnel. Using the protection of these burrows, these fish will hover, feeding on plankton or other small organisms, ready to dart back in at the first sign of danger. They are territorial of the area around their burrows.

And, of course, they use their jaws to do it. They excavate by grabbing hold of great mouthfuls of sand and depositing it in a pile. Then they get small stones and pieces of shell and carefully arrange them around the walls of their burrow to stop the whole thing caving in. Soon they have a delightful home to call their own. All they have to do now is spend time every day getting rid of all the sand that constantly gets swept in from outside. Dirty, filthy outside.

To keep outside at bay when they retire for the night, many Jawfish use a particularly large piece of shell as a door, or pile up some stones to block the entrance so they rest safe and snug and not have to worry about muggerfish or sea burglars or whatever other miscreants may come out at night.

By day, Jawfish stay close to home. If they feel particularly safe they may wander around a short distance away from their burrow or hover above the entrance. Often they will only allow their head to poke out. Now they can use their enormous, bulging eyes to survey their surroundings, and the large, downturned mouth gives them the facial expression of someone who disapproves of what they see.

They don’t always disapprove. Sometimes they eat. A lot of the smaller Jawfish will snap up tiny, planktonic creatures as they drift by. Larger ones can apply their jaws to small fish and crustaceans.

Yellow head jawfish Photo by Kevin Bryant
Yellow head jawfish Photo by Kevin Bryant

But hunger isn’t the only circumstance that will inspire a Jawfish to use her jaws in anger. You see, Jawfish don’t only own an abode, they own land, too. They stake a claim on the grounds surrounding their burrow and woe betide trespassers. An angry Jawfish may physically pick up and throw out interlopers. Other times, quite possibly with a battle cry of “get orf moi land!” they’ll spit sand at them.

Mouth full of minors Photo by Kevin Bryant
Mouth full of minors Photo by Kevin Bryant

After eating, building a home and defending their territory, it’s time to put those jaws to work on more pleasant tasks.

Come breeding time, some Jawfish use their jaws during courtship. Males try to show females that they have the biggest and mightiest jaws of them all. Why?

Jawfishes are mouthbrooders, meaning their eggs hatch in their mouths, where the newborn fry are protected from predators.

The mating ritual is different in each species. However, the process usually begins in the dawn or dusk of a full or new moon, with the male gaining the attention of the female. If accepted, the female will follow her male counterpart into his cave, or in some cases a third, neutral cave built for the mating ritual. The egg clutch is first laid by the female, then fertilized by the male.

Because after she lays her eggs and he fertilizes them, it’s up to him to look after them. And he uses his jaws to do it. He picks up hundreds of eggs in his mouth and incubates them for a week or two before they hatch.

The eggs are easily seen bulging from the male’s mouth. The eggs were roughly .8mm in size, with an estimated 300 – 500 eggs in the male’s mouth.

There he sits, massive eyes ever watchful, massive mouth full of hundreds of tiny, sparkling eyes peering out from within the brood.

They hatch soon enough, spew forth from his mouth and it’s not long before the youngsters are big enough to start building tiny homes of their own.

What an inspiration! Such power. Such potential. Right there, all along. Staring at us in the mirror. Right under our noses this whole time.

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August 27, 2018 |

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