They live in burrows, the males look after the eggs, and they can puff up their mouths to look big if threatened. Welcome the jawfish.
Packed with personality, meet the colourful, diverse, burrow-dwelling members of the jawfish family.
WHILE WE should be careful not to project human attributes onto the fish in our care, some really do seem to have wonderful characters and a unique, fishy ‘personality’. Many are also beautiful, some are pretty disease resistant, and there are even species that offer the opportunity to spawn and rear them at home. Some of those types can be found within the fabulous jawfish of the Opistognathidae family.
The Opistognathidae is a group of small to medium-sized marine fish that range from just a few centimetres in length to around half a metre – specifically, a species originally named the Giant jawfish, Opistognathus rhomaleus. There are currently four genera contained within the family, of which one, Opistognathus, accounts for the vast majority of species, with over 65 currently described, and is also home to all of the species available in the hobby – it's represented by species from all around the globe.
The other genera are Lonchopisthus, a group of largely deeper-water jawfish restricted to the subtropical and tropical Atlantic; Stalix, a genus where all member species are found in the Indo-pacific; and a more recent addition to the family, the genus Anoptoplacus – currently represented by a single species, the tiny, deepwater Caribbean pygmy jawfish, A. pygmaeus.
The jawfish’s common name derives from the size of its head, which can be 'inflated' through muscular contractions to appear substantially large, and make the fish look more of a fearsome proposition to predators than it actually is.
Housing and feeding
Jawfish have a well-developed sense of place; a phenomenon called site attachment. They aren’t natural roamers, instead finding a place they like and staying there – often for the entire duration of their lives. Many of the best fish for marine aquaria are those for whom natural territories could be contained within the confines of a fish tank and many jawfish tick this box.
There has been much written on the requirements of jawfish with regard to minimum depths of substrate but, as with so many aspects of the marine aquarium hobby, any generalisation only tells part of the story. In their natural environments jawfish reside in burrows that they excavate and tend to themselves. These can differ in composition and form between species and also are influenced strongly by the types of substrate available to a particular individual.
Many texts concerning jawfish stress the need for substrate depths of between 7cm and 15cm as an absolute minimum. The truth is that many species will make do with only a fraction of this, and some are highly resourceful in what they will use to construct a burrow in which they feel at home.
I've seen certain Caribbean species pull substrate from all over the aquarium to construct a conical burrow, with an opening at the top that gave it an appearance much like a volcano. Others seem happy beneath rocks and in crevices that they fill and shape with rubble and sand from the surrounding locale, which they will inhabit when other areas of the aquarium seem to offer a more textbook habitat for them.
To closely simulate their natural environment, deeper substrates with a mixture of rubble, sand and gravel are preferred, but these aren't always favoured by aquarists.
Jawfish love to dig and fuss about their burrows, and watching them do this and then return to sit inside their latest creation is part of the enduring appeal of these fish. However, placing them into a well-established aquarium can cause problems as they disturb detritus-bearing sand by digging and can potentially undermine rock structures. It’s a
shame as jawfish are reef-safe and can be trusted with all but the tiniest fish and ornamental shrimp, and are otherwise wonderful aquarium fish.
However, the biggest hazard for a jawfish is probably an open-topped tank. Use of a lid is compulsory to prevent them from leaping from aquaria. Jawfish are particularly nervous when first stocked into the aquarium and it's no coincidence that it's during the first weeks after introduction that they're most likely to be found outside the tank.
Some jawfish are planktivores whereas others consume a variety of benthic invertebrates – small crustaceans and worms. Some include small fish in their natural diet. Most, if not all, should readily accept frozen diets such as Mysis and brineshrimp in the aquarium and many can be weaned onto flake and pellet diets.
Although it's difficult to argue that jawfish will thrive in otherwise-peaceful aquaria with a handful of boisterous tankmates – something that’s pretty much true for all fish – they can show remarkable resilience when placed in aquaria with the likes of tangs and dwarf angelfish. But, as with so many fish combinations, compatibility can be highly context-specific – placed with jawfish, aggressive species like dottybacks and some wrasse often go on to be bullies.
It pays to make jawfish an early addition to any set-up, allowing them time to create a place to call home and develop it in a relatively sedate environment. Add the busier fish afterwards and your jawfish will feel much more secure.
Male jawfish typically court females before spawning and it's then that any differences between males and females can be observed. The Blue spotted jawfish male, for example, develops a white front half, while the rear part of his body turns almost black as he darts up and down in the water column – this is his way of displaying his readiness to mate. In O. solorensis the female appears bright yellow during
In their natural environments jawfish reside in burrows that they excavate and tend to themselves
the breeding season. Unfortunately, these visual cues aren't likely to be displayed by fish in shop tanks, so buying a group and allowing them to sort themselves into a little colony where space allows is often the best way to proceed. However, don’t try this in smaller aquaria unless you’re 100% confident that the specimens will tolerate one another’s presence. If in doubt, keep jawfish singly.
Breeding can occur in the burrow of either sex, or sometimes in a halfway house built by the male for the purpose. Successful spawning results in a mass of fertilised eggs that are incubated in the mouth of the male. Different species have varying brood sizes, but many consist of hundreds of eggs that must be regularly ventilated by the male. In the case of the yellowhead jawfish, he will partially spit out the eggs and take them back into his mouth.
Male mouth-brooding is seen in other marine aquarium fish, notably the Cardinalfish (Apogonidae). The male invests in the brood, limiting the number of his offspring annually, and sticking with the eggs from one female at a time – some species are practically monogamous. This way, he can guarantee that the brood he is incubating is actually his.
Among the jawfish you'll find everything from the affordable to the exclusive. I've a feeling jawfish are still to have their day and, as the aquatics world expands its collective knowledge, they'll likely be shown to have even more to offer.
To fully appreciate them we must be able to tolerate their relentless re-aquascaping of the substrate and their potential to bury corals or strip the aquarium base of sand and gravel.
Are Jawfish so great we're prepared to turn a blind eye to such antisocial shenanigans? Only you can decide…
Jawfish can burrow in many types of substrate.
ABOVE: Breeding can take place in his burrow, hers or a halfway house.