Back in the early days of the marine aquarium hobby (the 1950s), there was a limited choice in saltwater livestock. It’s hard to believe now, but there were nary any reefkeepers – in fact, the number of invertebrates offered for sale could be counted on two hands. Fish selection wasn’t much better, with most offerings coming out of the tropical West Atlantic. These included some hamlets (Hypoplectrus spp.) and royal grammas (Gramma loreto), as well as the occasional wrasse, angel, butterfly and damsel. The yellow-headed jawfish is proudly included in this saltwater collection because it has many traits that make it suitable for the aquarium. This species is relatively easy to collect, holds and ships well, adapts well to captive conditions, and it’s good-looking and behaviorally interesting. This species needs adequate bottom space (1 to 2 square feet per specimen) made up of mixed rubble and soft sand to allow permanent tunneling. It also needs a complete top to prevent it from launching out of its system.
Jawfishes are closely related to grammas and dottybacks (Pseudochromids) in terms of both behavior and evolution, though they look more like gobies or blennies. Jawfishes have cylindrical and oblong body shapes, long continuous dorsal and anal fins, and big mouths (Opisto means “behind” and gnath means “mouth,” referring to their receding jaws). These characteristics and their enormous all-seeing eyes make them unmistakable. Another more distinguishing characteristic is their bodies being covered with cycloid scales, though their heads are “naked” of scales, spines and other processes. This feature aids them in their continuous burrowing.
The one trait that separates opistognathids from all other perciforms is the arrangement of fin supports in their pelvics. These have one spine and five soft rays (the inner three weak and branched, and the outer two stout and unbranched). Opistognathids are all marine species that come from the western and central Atlantic and Indian oceans, and both coasts of the Pacific Ocean. There are three genera (Opistognathus, Lonchopisthus, Stalix) with about 60 described species with several others under study. Most are less than 4 inches, though a notable few (some Gobioides and Periophthalmodon species) attain almost 20 inches in total length.
The pearly or yellow-headed jawfish (Opistognathus aurifrons) is one of the most popular aquarium fish collected in the tropical West Atlantic. It deserves its status as the most-collected-and-kept jawfish species. It has a light blue anterior, grading to creamy white and yellow toward the front half; it spends more time outside of its tunnels than other jawfish once established. This species grows to 4 inches in length.
The yellow-headed jawfish spends 99 percent of its time either all the way in its burrow or with just part of its head exposed. Even if you provide the correct peaceful settings and give them conspecific tankmates, most individuals continue to be secretive. About the only time the aquarist generally sees a jawfish all the way exposed is during feeding sessions or territorial displays. In fact, it is not uncommon for jawfishes to do as symbiotic pistol shrimp and goby combinations do: close off the openings to their burrows at night, and even during the day, if they don’t want to be disturbed.
If your jawfish go missing for days, don’t overreact and imagine the worst – and definitely don’t start taking the tank apart. Jawfishes can easily go a week to 10 days without feeding. More often than not, they’re still there, hiding and doing whatever it is fish do when they want to remain out of the limelight. And if indeed the worst has occurred, their mass is small enough that scavengers and decomposers will clean up the remains without incident.
Ideally, these fishes are best presented in a species-only setting. If they are to be mixed with other organisms other than sedentary ones like corals, these tankmates should be few in number, nonpredatory and nonaggressive – this means no triggers, eels, large bass or wrasses. Too often, one finds that jawfishes are lost due to stress and undernourishment from being placed in too-active, too-crowded settings. Give yours room and peace.
Yellow-headed jawfish are about as reef-safe as a marine fish can be. They don’t chew on stinging-celled life, and they leave clams, shrimp of any size and all other fish alone. Good tankmates are slow-moving fish that prefer the medium to upper water column. Some good tankmates include cardinals, fancy basses (Anthiines) and fairy wrasses (Cirrhilabrus spp.). Another great gauge to use is to seek out the types of life found in these fish’s tropical West Atlantic setting, and then mimic (make a biotope) of this setting, including livestock. Gramma loreto is found in rocky outcroppings near the sand flats that O. aurifrons calls home, as are tropical West Atlantic butterflyfishes, hamlets (Hypoplectrus spp.), indigenous damselfishes and much more. You can find quite a few macroalgae species, sponges, gorgonians and more from this part of the world that are regularly offered in the trade.
The general rules of choosing marine fish also apply to jawfishes. First and foremost, look for robust and well-adjusted specimens. Emaciated individuals that are not burrowing are likely doomed.
If you’re interested in breeding these fish, you will need to spend some time closely observing specimens as they interact. Jaws aren’t easily sexed by morphological or color differences, and thus it’s best to let them do the sorting themselves. Otherwise – and especially if buying smaller captive-produced individuals – place five or six in a suitable setting and allow them to pair up.
System size is important with this species of jawfish, though O. aurifrons is highly social compared to others in its family. Provide 2 square feet of uncrowded bottom space for the first individual and 1 square foot to share for every additional jawfish. Having more than one specimen is highly recommended, though the species can do well solo; but with more of them, you will experience more social interaction and have more fun keeping them.
Use a 3- to 4-inch-deep mixed-grade substrate that includes some bivalve shells for cover. The jawfish is a prodigious burrower and will be unhealthy if not given the proper media. The blending of finer sand with coarser rubble bits in at least one area allows the jawfish to reinforce its tunneling, and even if provided, you may find yours digging under rockwork (assure your rock is sitting directly on the bottom of your system to prevent toppling due to destabilization).
If you have a concern that your jawfish may burrow too much into your substrate, you can do what folks with many types of plenum arrangements do: lay in a cover of plastic screen door mesh with just some gravel over it in the areas you’d not have them dig.
Being true reef fish, jawfish require reef-quality water and the filtration to accomplish this – perhaps doubly so, as their digging around can lead to a good deal of detritus rising into the water column. Use a relatively large refugium with your system to provide continuous feeding, as well as the best conditions.
Most settings call for using something in the way of a feeding tube, syringe or turkey baster to get food items to the general vicinity of your jawfish. Otherwise, unless there is a good deal of endogenous live food production (e.g., a large, healthy, tied-in refugium), then your jawfish may be undernourished.
I am a huge fan of using vitamin and HUFA (highly unsaturated fatty acids) supplements on a periodic (once, twice a week) basis by soaking foods to be offered for a few to several minutes ahead of use. There are numerous reports of likely malnutrition-related blindness in this species and spontaneous cures brought about apparently from the use of such additives.
I put all jawfishes in the category of “better not to quarantine,” along with most gobies, blennioids and others. I say it’s better not to quarantine them for the sake of preventing too much stress, death from stress and starvation. It is better by far to do a cursory pH-adjusted freshwater bath (five minutes or so) with or without methylene blue to rid the fish of external parasites. Then place the specimen directly in the display tank. Though less susceptible to the usual external parasite scourges than most marines, jawfishes do contract them and don’t do well with toxic treatments (metals, dyes, formalin). You are encouraged to move all fish to a separate treatment tank and utilize quinine or chloroquine phosphate if you’re keeping opistognathids.
Opistognathus aurifrons has been cultured to maturity in aquariums, though most specimens are still wild-collected. They may be gathered or set up as pairs for your acquisition. Most are found paired in the wild, with males doing a ritualistic “dance” to signal intentions to their mates. These consist of arched body approaches, with their fins erect at 90 degrees to their bodies. If the fish spawn, males fertilize the eggs and pick them up in their mouths. Fertilized eggs are orally incubated for a week to 10 days, depending on water temperature. Commercial breeders move males with young to separate systems to provide peace and protection from predators. Incubating males are provided with pieces of PVC pipe for habitat.
The greatest and most common problem occurs with providing sufficient food to the young once their small yolk sacs are absorbed after two to three days. Many early attempts involved rotifers as initial foods, but it is likely that small species of copepods (collected or purchased as stock cultures), followed by newly hatched brine shrimp, are best. Young are released, and they become surface plankton and float about for two weeks. After this, they metamorphose into small bottom-dwelling versions of the adult form, growing quickly under ideal conditions.
The yellow-headed jawfish has been an integral part of the marine aquarium hobby from its origins in the 1950s. Though it has been commercially and privately spawned and reared in captivity, specimens are still mainly wild-collected. These prove to be hardy shippers and adapters to captive conditions. They demand only a not-too-busy setting with some depth of mixed substrate to burrow and regular small animal feedings. AFI