Easy Care Saltwater Fish: The Yellow-Headed Jawfish
Opistognathus aurifrons has been a favorite in marine aquariums for more than 60 years
Bob Fenner |
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The pearly or yellow-headed jawfish (Opistognathus aurifrons) is one of the most popular aquarium fish collected in the tropical West Atlantic. Photo credit: Bob Fenner.
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.