Jawfishes

/The Conscientious Marine Aquarist

Jawfishes, Family Opistognathidae

Bob Fenner

Opistognathus macrognathos

"You spent how much money on what?" "Where is it?" "More than one?" "You're joking; where?" "For those fish heads?" "Are you out of your mind?" "Who cares how beautiful they are, if all they do is hide in their holes all day?" "I should have married that stamp collector!"

Jawfishes make for endlessly interesting aquarium fishes, where provided with adequate sand and rubble to produce their famous tunnel works. They're hardy, lightning fast and fantastically interactive with each other; ideal tankmates for peaceful fish, invertebrate and full-blown reef systems.

These fishes are mouthbrooders, with the males practicing oral incubation. Where do they live? Almost always just having their heads exposed in their at times elaborate, mouth-dug burrows.

Classification:

What are the Jawfishes in relation to other families of fishes? If you look through the literature, you'll find the Jawfishes are moved around different Orders more than a floating thermometer in a tank without a suction cup.

In appearance they're kind of Blenny-like, sort of Goby-ish, but really more similar to the Grammas (family Grammatidae) and Dottybacks (Family Pseudochromidae) in their evolution and behavior. Grammas, Dottybacks and Jaws all have an interrupted lateral line high on the flank, terminating mid dorsal; and an arrangement of paired fins with the pectorals located behind the pelvics. What's more, all three groups build burrows and are mouthbrooders.

Jawfish exhibit oblong body shapes, long continuous dorsal and anal fins and way-too big mouths ("Opisto" = behind, "gnath" = mouth, is in reference to their receding jaws) and enormous, all-seeing eyes make them unmistakable.

Some other more defining, distinguishing characteristics are their bodies being covered with cycloid scales, though their heads are "naked" of scales, spines and other processes. This feature aiding them in their continuous burrowing.

The one trait that separates the opistognathids from all other perciform (Order Perciformes, the largest order of fishes) is the arrangement of fin supports in their pelvics. These have one spine and five soft rays (inner three weak and branched and the outer two stout and unbranched).

Opistognathids are all marine; western and central Atlantic, Indian and both coasts of the Pacific. There are three genera (Opistognathus, Lonchopishtus, Stalix) with about thirty nine described species and many others under study. Most are under ten centimeters, though a notable few attain half a meter in total length.

Species of Greatest Aquarium Interest:

Opistognathus aurifrons (Jordan & Thompson 1905), the Pearly or Yellow Head Jawfish is one of the most popular aquarium fishes collected in the tropical west Atlantic. It deserves it's status as the most collected and used Jawfish species; being a light blue anteriorly, grading to creamy white and yellow toward the rear half, and spending more time outside of it's tunnels than other jaws once established. To four inches in length. Note gravel at wholesalers in this image.

Bigger PIX:
The images in this table are linked to large (desktop size) copies. Click on "framed" images to go to the larger size.

Opistognathus macrognathus Poey 1863, the Banded Jawfish. Tropical west Atlantic. To eight inches in length. Here doing what the family does most all the time. Lie in wait for a food item or territorial challenger to come/happen by. Photo taken in St. Lucia, Caribbean.

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The images in this table are linked to large (desktop size) copies. Click on "framed" images to go to the larger size.

The Blue-Spotted Jawfish, Opistognathus rosenblatti Allen & Robertson 1991, of Mexico's Sea of Cortez (Gulf of California in older, less PC texts) is a real striker, with brilliant blue dots over it's overall dark brownish body. The males become bright white in the front half of their bodies during spawning and courtship. To six inches total length. This one in captivity.

Opistognathus whitehursti (Longley 1927), the Dusky Jawfish. To 14 cm. Western Atlantic: southern Florida, USA and Bahamas to northern South America. http://fishbase.org/summary/SpeciesSummary.php?id=3689

Undescribed Species: There are several

Opistognathus sp. U1. One of many as-yet undescribed Jawfish species. Dr. Randall (pers. corr.) told me once that he had backlogged at least a dozen or so in this family... let's hope he gets around to them soon. N. Sulawesi pix.

Bigger PIX:
The images in this table are linked to large (desktop size) copies. Click on "framed" images to go to the larger size.

Opistognathus sp. U2 Gold Specs Jawfish. Mabul Malaysia. A male with a mouthful of eggs.

Opistognathus sp. U3, another undescribed species in the Lembeh Strait, N. Sulawesi.

Verticals (Full/Cover Page Sizes Available)

Opistognathus sp. U4, a shot I took at House of Fins, CT in 2012

Bigger PIX:
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Bali 2014

Dusky Jawfish, Opistognathus whitehurstii are camouflaged beauties that deserve more attention. Their brown mottled bodies are accentuated with glowing red to aqua eyes. To 3.2 inches.

There are other species collected for the hobby from the Atlantic like the Mottled Jawfish (Opistognathus maxillosus) that are generally offered as "miscellaneous" Jawfish. I have yet to find any that did not do well in captivity.

Selection:

Most Jawfishes are collected by way of "organic" methods; a poker is dug in near the tunnel hole, leveraged at an angle driving out the occupant, and a fine mesh quickly blocking re-entry. Due to small gas-bladder size they can be quickly raised to the surface.

Some Caribbean collections still utilize chemical tranquilizers and these shipments often have high losses. My usual admonition here re deposits and waiting on questionable livestock. If a week or two goes by and the western Atlantic jaws are still frisky, I'd buy them.

Environmental Conditions

Habitat/Display:

Unlike the related Dottybacks and grammas, the Jawfishes live on sandy reef flats in vertical burrows. They fully utilize and constantly rearrange sand and rubble, shells and small stones in making their burrows and entrances. They definitely need to do the same in captivity. A good mix of substrates for them is about three quarters fine (1/16-1/4"), and one quarter coarse (1/4-3/4", coin shape/size pieces) material, of a 2-3" depth minimum.

Due to their peaceful, secretive natures, the smaller species of Jawfishes make excellent choices for non-aggressive invertebrate and reef systems.

If the group has a fault that can be cured by habitat modification, it is jumping. Keep your tank covered, completely.

Filtration:

You might assume that because of their size and sedentary life style, the Jawfishes wouldn't require much in the way of water cleaning; but due to their digging and production of cave-stabilizing slime it's better to have more than less water agitation, four or more turn overs per hour.

Also you might be considering abandoning the use of undergravel filters if you're keeping jaws, as their burrowing would disrupt their circulation. Two suggestions here; if you're going to use u/g ponder the possibility of installing a fiberglass or plastic mesh barrier between it and about an inch of gravel for filtration's sake, with the Jawfishes territory above. Secondly, be wary of utilizing air-driven lifts with these fishes as they do not appreciate the bubbling, gurgling sounds they produce.

Territoriality:

Definitely, these are the species you want to keep it you're into studying overt intra-species behavior; and it should be just one Jawfish species per system.

Small varieties (less than four inches) can usually be kept on per ten gallons or so. In the wild the pearly jaw lives as close as a foot apart from each other, the blue-spots' individuals are about one meter spaced in their colonies. Too much less than this in captivity and you can expect perpetual war.

Bruisers like the eighteen inch Opistognathus rhomaleus are one to a tank for sure.

Opistognathus rhomaleus Jordan & Gilbert 1882, the Giant Jawfish. Eastern Central Pacific; Baja to the Islas Revillagigedos. To eighteen inches in length. Here at the Birch Aquarium, San Diego, California.

Introduction/Acclimation:

The Jawfish should be some of the first fishes introduced, especially if you are crowding them population wise; and introduced all at once.

Predator/Prey Relations:

These fishes are naturally timid and should not have aggressive or fast swimming tankmates.

There are a large number of predatory fishes known to "elicit a strong fright reaction" including reef groupers, large Tilefishes and Wrasses, Jacks, Snappers, Triggers... I wonder why? Keep jaws with small peaceful fishes (like the Neon Gobies and Porkfishes we've discussed), or easy-going invertebrates.

Reproduction:

In Opistognathus aurifrons males orally incubate the eggs for about one week. Off Florida, this species breeds from Spring to Fall. Females are quickly courted by males who sport blackish dots on their heads during this time, spreading their mouth and fins wide apart. Courting and cave spawning generally occur at dusk or dawn. The young are pelagic and feed principally on small crustaceans for 2-3 weeks before settling and digging their first tiny burrows.

The yellow-headed jaw is hard to distinguish as male/female, but other species (blue-spotted, the Atlantic Yellowhead Opistognathus gilberti) males show marked color changes at breeding times.

Some species of opistognathids have been bred and reared in captivity, but most are still wild caught.

Foods, Feeding:

These fishes are carnivores; feeding by hovering and dashing out and back from their burrow like greased lightning on floating zooplankters.

In captivity they are best specialty fed by a turkey baster-blast-method. A crustacean food (defrosted krill, frozen brine shrimp), or minced shellfish is sucked up and discharged near the mouth of the fish's burrow. Occasional live foods are of course highly appreciated.

On-arrival feeding strikes of a week are not unusual; try a little live food (brine shrimp) if this time goes beyond.

Disease:

Perhaps owing to their sliminess, burrowing habits, and predatory pressure (the weak one's get eaten quickly) the Jawfishes are remarkably disease free and infection resistant. Professional collectors administer freshwater dips of 3-5 minutes duration as a preventative.

If necessary for treating tankmates, opistognathids are not sensitive to requisite 0.15 ppm free copper. These species are very hardy overall.

Close:

Though your friends and family may laugh with glee when first finding out how much of your discretionary income was expended on such bug-eyed fish that "you can't even see"; be patient. The jaws will eventually come out and amaze all with their speed and industriousness.

Bibliography/Further Reading:

Baensch, Hans A. & Helmut Debelius. 1994. Marine Atlas, v. 1. MERGUS, Germany.

Chlupaty, Peter. 1978. The fish with the golden head. TFH 8/78.

Colin, Patrick L. 1972. Daily activity patterns and effects of environmental conditions on the behavior of the Yellowhead Jawfish Opistognathus aurifrons, with notes on its ecology. Zoologica 57(4):37-169.

Fenner, Robert. 1996. Jawfishes. TFH 8/96.

Fenner, Robert. 1998. The Conscientious Marine Aquarist. Microcosm, VT. 432pp.

Kerstitch, Alex. 1979. The first record of the courtship behavior of the Blue Spot Jawfish. FAMA 9/79.

Kerstitch, Alex. 1988. Master builders (re the family). SeaScope Winter 88.

Lobel, Phil S. 1982. The Yellowhead Jawfish; Opistognathus aurifrons. FAMA 4/82.

Michael, Scott. 2000. The whimsical Jawfishes. AFM 8/00.

Nelson, Joseph S. 1994. Fishes of the World, 3rd ed. John Wiley & Sons, Inc. NY.

Noyes, John C. 1974. Yellowhead Jawfish. Marine Aquarist 5(2):74.

Noyes, John C. 1987. The Dusky Jawfish, Opistognathus whitehurstii. FAMA 4/87.

Randall, John E. 1968. Caribbean Reef Fishes. TFH Publ.s, NJ.

Stratton, Richard F. 1993. The Yellowhead Jawfish. TFH 3/93.

Straughan, Robert P.L. 1965. The Pearly Jawfish, a sea nymph. TFH 1/65.

Young, Forrest A. 1982. The Yellowhead Jawfish; breeding the marine mouthbrooder in captivity. FAMA 4/82.

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