Fish Tales by Henry C. Schultz III

Let's Jaw About Jawfish

Lately, it seems there has been a lot of confusion about jawfish in reef aquariums. With the advent of live sand substrates and today's popularity of oolitic or "Southdown" sand, many hobbyists are left with a feeling that jawfish are no longer a great reef community fish. I completely disagree with this notion, and will explain why as this article progresses.

About the Family

The Family Opistognathidae, otherwise commonly known as jawfish, is comprised of three genera and nearly 40 described species with possibly another 30 un-described.

Since Opistognathus are the most popular genera among aquarists, Lonchopishtus, and Stalix will not be discussed.

Roughly 23 described species bear the Opistognathus name. Opisto comes from the Greek word opisthen, meaning 'behind,' and gnathus meaning jaw. These species are the ones that are most often of interest to the hobbyist due to size, availability, and coloration. Opistognathids can be found in the western and central Atlantic, Indian, and both coasts of the Pacific Oceans. They sport a long, continuous dorsal fin of 9 - 12 spines, and a spine made of three weak-branched inner rays and two stout, un-branched rays on either end. All jawfish are mouth brooders, and all live in a den that they dig with their mouths.

The two most commonly kept jawfish are O. rosenblatti and O. aurifrons. I will concentrate my discussion on these two fish. From here on in the discussion, when I refer to "jawfish," I will mean these two species. I will touch on a few additional species at the end.

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The Blue Spot Jawfish. One look and you can understand why some hobbyist don't balk at the $200 price tag.

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Dusky jawfish like this one rarely hover above their burrow. Instead, they sit with just their head exposed, watching the world go by, and waiting for a meal to pass overhead.

Captive Care Requirements

Lately, jawfish have been getting a bad rap when it comes to the current trend of a deep, live sand bed. Many hobbyists complain of these fish constantly moving sand, always building new borrows, digging to the bottom of the tank, clearing the sand away from ½ of a tank, or even eating the life of the sandbed. The latter is a completely unfounded belief, and simply not true. When added to a sandbed comprised of sand <5mm in diameter, a jawfish will do exactly as hobbyists otherwise complain. The hobbyist is left in buyer's remorse because the fish wreaks havoc on the sandbed, largely due to the hobbyist not supplying the fish with adequate den building materials.

Captive care should mirror their natural environment as much as possible. This is not possible in most home aquariums due to size restraints, but with good planning, a close replica can be achieved. Jawfish are always located on reef flats at depths ranging from 10 feet to 150 feet. They prefer to hover up to 5' above their den, always having a 360° view of their surroundings. Without an extensive view in all directions, they will hang lower than usual or may only extend their head outside their den. This reclusive behavior also occurs when actively swimming fish are present. Their dens range from 4 - 9" deep, extend nearly 9" wide, are 2.5" tall, and are comprised of mostly broken coral branches, pieces of coral limestone, bivalve and snail shells, and assorted pieces of hard material (Michael, Coral Realm). They feed entirely from the water column with roughly 85% of their diet being zooplankton (Randall, '67).

So what does all this mean? Plan ahead. Jawfish should be the first fish added to the home aquarium. It is harder to get them acclimated once other fish are established. This does not mean if your aquarium already has inhabitants that you cannot keep these fish, but it does make it tougher to acclimate them.

Assuming we are planning ahead, the ideal sandbed for a jawfish will be at least 10 - 12" deep. Emphasis on "ideal." Sometimes "ideal" is not always realistic. In such cases when 12" of sandbed is not realistic, I would consider 6" as being the absolute minimum. This is a personal observation only. Others have recommended a 3" sandbed as a minimum (Fenner, Wet Web Media). When you take into consideration that the minimum depth for a jawfish's den in the wild is 4", a 3" sandbed seems extremely inadequate. You can use fine grain, or "Southdown" sand, but be prepared for the jawfish to clear away a large area on his first night. When I say, "be prepared," I mean with appropriately sized rubble for the jawfish to use in building its den. This includes most any rubble larger than 10mm in width. Don't forget to include plenty of broken coral branches, pieces of coral limestone, bivalve and snail shells. As time goes by the jawfish will construct a den for itself, slowly using the rubble you supply to build its new home. As the rubble gets used, keep replacing it with more. Soon enough, you'll have your sandbed back in order, and the jawfish will have it's home constructed. A nice finishing touch on the den is usually a snail shell or its equivalent being used as a "roof" of sorts. The jawfish will pull this "roof" over the den entrance when it retires for the evening, and remove it when it wakes in the morning!

Since the jawfish consumes a great deal of zooplankton, feeding is easy. Enriched brine, mysis, plankton, and Formula I should be readily accepted. If newcomers are finicky eaters, it may take live brine or live blackworms to entice a feeding response. In passive tanks the jawfish will become an aggressive eater, actively roaming around the tank in search of its next tasty morsel. However, in a tank with active fish, especially those that are hyperactive at feeding time, spot feeding with a turkey baster is most likely going to be required.

One common myth regarding jawfish care in our tanks, is that strong lighting should be avoided. Since jawfishes are found throughout reef flat depths, most any aquarium lighting will be sufficient. It is improbable that strong lighting has any negative effects.

Bringing One Home

Your deep sandbed is ready, rockwork is stable and supported, and you have plenty of excess rubble on hand. Once you have the fish, follow typical acclimation procedures. If you introduce the fish during the daylight photoperiod, you can expect the fish to dart for rockwork. It will usually remain hidden in the rocks for the first day, though on occasion the daring jawfish will begin its burrow construction. This is more common when it is the first fish into the tank.

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A male Opistognathus aurifrons.

A major concern for the newly acquired jawfish is their tendency to jump from open top aquariums. It is absolutely imperative that the home of a newly acquired jawfish is covered! Some will use glass tops, but this is usually frowned upon in the hobby for various reasons. So some others, myself included, will use egg crate fitted over the top of the tank. Egg crate can be found in the lighting department of most any home improvement store. Since the holes in the egg crate are large enough for a jawfish to slip through, it is necessary for you to use some sort of screening or netting laid over the egg crate. I use window screening, though most any type of screen or net could work. If your tank has appropriately selected tankmates, this is only temporary. If you have a full canopy that covers the tank, then additional measures are not required. Just make sure there are not even the smallest of holes available for it to slip out of. Most enclosed canopies still have an open back. Make sure this is covered. Once the jawfish's burrow is constructed, the likelihood of jumping dramatically decreases, and with the appropriate tankmates, it is virtually non-existent.

The Den in a Home Aquarium

Though the fish is typically diurnal, they will spend their first night constructing the first stage of the den while under the cover of darkness - their only other defense besides their den. Don't expect the den to be finished overnight. Though they keep only one den under typical situations, they will be remodeling it daily. The remodeling process is underground and is unseen by the aquarist, except for the occasional mouthful of sand that gets deposited alongside the burrow opening and traded for a larger piece of carefully chosen rubble. Remember, as the rubble disappears, keep replacing it. If it is getting used never stop replacing it.

As noted above, a jawfish prefers to have a 360° view of its surroundings. Given the confines of our small tanks, this is rarely possible. As a result, one of two types of dens is constructed:

1) When appropriate conditions prevail, a den in the open substrate will be formed. This is obviously a good sign that your jawfish is acclimating well and that you have supplied a suitable habitat.
2) The other type of den, what I like to call a "security den," occurs when the jawfish digs under some rocks and usually remains tucked into his hole with only his head or half of its body showing. This results from any number of factors ranging from: inadequate sand and rubble composition, not enough open sandbed, or even inappropriate tank mates. When this type of den occurs it is best to re-evaluate the habitat you're supplying and make sure you are not overlooking something.

Tank Mates

Choosing the appropriate tank mates for your jawfish is a task not to be taken lightly. With the wrong mix, you'll either kill the fish or never see it.

Natural predators should be avoided at all costs. This includes groupers, lionfish, adult tilefish, and any large piscivore. Immature tilefish, Halichoeres gamoti, and H. bivittatus will all pester and steal from the jawfish (Michael, Coral Realm). All predatory starfish should be avoided, including the genus Ophiarachna.

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Starfish like this Green Brittle Star should be avoided in a jawfish aquarium.

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Is it any wonder why jawfish are uneasy around the presence of Ophiarachna?

Fast or active swimming fish should also be avoided. All surgeonfish, angelfish, and butterflies fit into this category. Additionally, certain wrasses will fall into this category. Any larger fish that darts or becomes hyperactive during feeding may potentially cause problems. If you want to keep your jawfish with any fish that fit into this category, it is highly recommended that you never remove your cover from the aquarium. Otherwise, in time, you will find your jawfish on the floor.

Small gobies might be best kept in a different tank unless they establish a homestead and don't wander far from it. A jawfish does like to keep a perimeter around its den, and will usually defend this perimeter against small gobies. In my own observations, this occurred with my White-rayed Shrimp Goby, (Stonogobiops, sp.). Occasionally, my Shrimp Goby would venture nearby the den of my jawfish. Each time, the jawfish would delicately grab the goby in its mouth and remove it from his territory. Usually, this was roughly 12" away from the opening of the den. The first time I saw this, I was astounded, fearing the un-timely death of my rare goby! When the goby swam away, I began to breath easier. This wasn't any easier to watch the second, third, or fourth time, either. Eventually, it grew on me, and I found it comical. Although not as often, yet often enough to note, the jawfish would grab mouthfuls of sand and spit them at the "attacking" goby. Again, no harm was done.

Gobies like this Stonogobiops sp. can become
a nuisance to your jawfish.

So what fish make good tank mates for jawfish? Cardinalfish, anthias, assessors, blennies, pipefish, and dragonettes will do well. Most gobies and some wrasses will also do well. The general criteria would be a passive, slow moving fish that is nearly equal in size or smaller.

Mating and Spawning

Mating, spawning, and the rearing of jawfish fry has been successful in home aquariums. A 4' tank is recommended for the pair in so much as natural territories of jawfish range from 1 - 3'. In spawning season (Spring through Fall), sexual dichromatism is present in some species. The Yellow head jawfish gains black spots on the ventral side of the head, while the Blue spot jawfish's posterior becomes white. Outside of spawning season there is no sexual dichromatism.

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 (Michael, Coral Realm). 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. Much like Banggai Cardinals (Pterapogon kauderni), male jawfish are mouth brooders. The eggs are easily seen bulging from the male's mouth. When Opistognathus aurifrons was studied, the eggs were roughly .8mm in size, with an estimated 300 - 500 eggs in the male's mouth. He incubates these eggs in his mouth for 7 - 9 days, after which time he releases the 4mm long fry. Shortly after the male releases the fry, the ritual can be repeated. At 15 days from release and 1.5cm long, the fry take to the sand and begin digging their den. Within one year they are full grown (Baensch, '94).

Raising the fry can prove to be tricky, although it has been completed successfully. First foods offered should be enriched Rotifers, to be followed by Artemia nauplii when the fry are large enough to ingest them.

Meet the Species

As noted earlier, Opistognathus aurifrons, or the Yellow head jawfish, is the most popular among hobbyists. They are, after all, attractive, hardy, and inexpensive. The attractiveness comes from the baby blue coloration throughout their body and their beautiful yellow head. Reaching a maximum size of 4", they originate from the tip of Florida and are found throughout the Caribbean. In most cases they will not bother invertebrates, although smaller ornamental shrimp may be eaten. When spawning, the male will hover in the open water and spread his fins wide and arch his body. Perhaps to show his readiness to the female, he opens his large mouth, and his head enlarges.

Second to O. aurifrons in popularity only because of price, is the Blue spot jawfish, Opistognathus rosenblatti. In general, expect a $100 price tag or more for these beauties. The Blue spot is found in the Gulf of California, usually at the base of cliffs. They reach 4" in length. The mating ritual of these jawfish begins when the posterior half of the fish becomes white. The male makes repeated dashes into its den. To the on-looking diver, only bright white flashes are seen. When not in spawning season, the background color of the fish is generally brown, and in some cases, a dirty yellow. Blue spots adorn the entire length of the fish. These species are slightly more aggressive towards each other, and a larger aquarium is recommended if you're trying to keep a pair. In the wild, the pair can be up to 10' apart from each other.

Nearly an identical twin to O. rosenblatti is Opistognathus panamensis, or the Panamanian jawfish. It differs from O. rosenblatti only by the blue spots and locale. In most cases, these spots are actually stripes, and, as the name suggests, it originates from Panama.

Several jawfish are commonly referred to as "Dusky jawfish." These would include Opistognathus macrognathus, Opistognathus maxillosus, Opistognathus scops, and Opistognathus whitehursti. Unlike the jawfishes discussed above, these are not planktonic feeders. They will consume small fish or shrimp if they fit into their mouths. Also, unlike their cousins, they lack attractive patterns or colors.

Also called a Spotfin, O. scops is imported from the east Pacific, Baja California, and the Galapagos. Overall, it is brown, with white spots throughout the body and a black spot encircled with white on the dorsal fin. These jawfish can get larger, up to 6". If you're looking for a jawfish to house with moderately more aggressive fish than that of the Yellow head or Blue spot, then this one is for you.

Another jawfish commonly referred to as the "Dusky" is O. whitehursti. It is the smallest Opistognathus at 3" and thus requires a quieter tank than the others. Like all other jawfish sold under the "Dusky" name, it is not a planktonic feeder. Shrimp should probably not be added to their aquarium unless they are intended as a meal.

There are other Opistognathus not mentioned. However, those generally don't get imported regularly or they get too large to house in home aquariums, thus they will not be discussed.

With their bug-like eyes and bucket-like mouths, jawfish win their way into most hobbyists' hearts. Their personality and hardiness are commendable. All too often, however, jawfish take the rap for destructive tendencies. In most cases the destructive habits are the fault of the hobbyist ignoring the needs of the jawfish.


References Cited:

Baensch, H.A., 1994. Jawfish. pp.1158 - 1167. Baensch Marine Atlas, Volume 1. Microcosm. Shelburne. 1215 pp.

Burgess, W.E., et al, 1991. Jawfish. pp.507 - 509. Dr. Burgess's Mini-Atlas of Marine Aquarium Fishes Mini-Edition. T.F.H. Publications. Neptune city. 1023 pp.

Lieske, E. and Myers, R., 1996. Jawfish. pp. 113 & 167. Coral Reef Fishes. Princeton University Press. Princeton. 400 pp.

Michael, S. W., 1999. Jawfish. pp.131 - 134. Marine Fishes: 500 + Essential-To-Know Aquarium Species. Microcosm. Shelburne. 447 pp.

Michael, S.W., 2000. The Whimsical Jawfishes. Aquarium Fish Monthly, 12:8, August 2000

Young, Forrest A. 1982. The Yellowhead Jawfish: Breeding in Captivity. Freshwater and Marine Aquarium Magazine, 5:4, April 1982.

On the Web:

Coral Realm
Wet Web Media
Breeder's Registry
Fish Base

Photo Credits:

Opistognathus rosenblatti - Inland Aquatics
Opistognathus aurifrons - Mark Friedrich
Ophiarachna incrassata (full shot) - anonymous
Ophiarachna incrassata (close up) - Vick Tagawa
Opistognathus sp. - Kedd Lytton
Stonogobiops sp. - Henry C. Schultz III

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Let's Jaw About Jawfish by Henry C. Schultz III - Reefkeeping.com