I was wondering if anyone has experience with these critters. I think the scientific name is Opistognathus aurifons I am specifically wondering what it eats, and how deep the sandbed should be. Will it decimate the critters already in the sand? I've found a lot of pictures, but no real information.

Everything others have said seems in agreement with my experiences, but I have a few further thoughts to add based on my experiences with several that I've had in a reef tank in our teaching lab here at Augsburg College.

Food

Ours started out eating pretty much any frozen food but would not take flakes or pellets (e.g. Vibragrow). It was nearly a year before any of them started eating flake food, and even longer before eating Vibragrow, but they eat anything now.

Also, jawfish seek food by hovering over their burrows or sitting at the mouths of their burrows, grabbing bits of food as it drifts by. Though they will eat any sort of small planktonic critters that swim or drift past (including newly released baby cleaner shrimp, chiton eggs, etc.), I have never observed them rooting around in the rocks or sand for food. So, I doubt that they would have much effect on the critters in your sand bed. They dig to make burrows to live in, not to find food in the sand. Also, amphipods and the like are most active at night, and at this time the jawfish are cloistered away in their burrows for the night (with a pebble covering and concealing the burrow opening), so nighttime predation on sand-dwelling inverts will not be a problem.

Sand / Gravel

It was recommended to me a few years ago before I got ours that I have at least 5" of substrate for them to dig in. I think this is a pretty good recommendation (the fish will probably grow to somewhere around that length or close to it), and is about what we have in our tank. It is important that there be a diversity of particle sizes (esp, not JUST fine sand), and gravel and particularly small bits of shell or rubble of various sizes are very important for them in their burrow construction. They actively seek out and gather small bits of rubble from their immediate surroundings to reinforce their borrows. At first it seems their burows are constantly collapsing on them (especially if you have a lot of fine sand like we have), and the fish are extremely busy digging them out at first. Eventually, the burrows get to be quite stable if the fish have the correct building materials.

Tank Layout, Rocks, etc

Ours really seem to prefer to build their burrows out in an open area rather than right in among the rockwork of the reef structure. This makes sense, given the sort of habitat they prefer in the wild (e.g. open sandy areas near reefs). They do seem to like to dig their burrows right next to rocks laying on the sand though, which helps stabilize their burrows, and they will excavate out a LOT of sand from underneath (and open brain corals or other sessile inverts sitting on the sand near the excavation sites will get sand piled on them). For this reason, make sure your rocks are stable and won't collapse when the sand underneath them is removed! . Ideally, you should build up stable short piles of rock on the bare bottom of the tank, and then add your sand/gravel/rubble until you have almost covered the rock piles. These will probably be favored places for digging burrows, and it is likely you will be able to influence borrow location by careful placement of these buried rubble piles. If possible, space these rubble piles well apart from each other to encourage the burrows to not be too close together.

Aggression

We started out with 3 young ones, which squabbled a lot but basically got along fine (eveyone stayed healthy anyway) in the open sand area in the front center of our reef tank (the layout of this tank and the jawfish can be seen at http//www.augsburg.edu/biology/aquaria/ ......if I were to set up an ideal tank for these fish, I'd have a much bigger expanse of open sand area than what we have). Then, a very large male bicolor blenny that was added to the tank started sitting in the jawfish burrows a lot (and would damage the burrows to give a tighter fit!), kicking/pulling the jawfish out. One of the jawfish died because I was really busy that week and didn't realize soon enough how much this was stressing them out, and I didn't get the blenny out of there soon enough. After the death of this fish, aggression seemed to increase between the 2 remaining ones, one of which ended up moving its burrow to a more secluded spot on the other side of the rockwork where the more aggressive one didn't normally see it. So, I'm wondering whether several (3 or more???) might be better than just two, especially if the tank is not really big, since the aggression is not so focussed on just one fish when more are present (?????).

Also, though yellowheaded jawfish established in burrows seem to be pretty hardy and resilient fish in some respects, they seem to be absolutely miserable and terribly stressed when they are without the protection of a burrow (and, as mentioned above, they can get really badly stressed by constant or even intermittent agression from other fish). They certainly are not fish to plan on moving around from tank to tank very much if you can possibly avoid it (I really don't know how in the world I would remove ours from their burrows without collapsing the burrows and burying the fish alive if I were to need to move them.... OK, actually I do know how I'd do this as I did do it once, but it was terribly stressful for the fish and I was afraid I wasn't going to be able to dig it out from under 4" of collaped sand without killing it). I've heard firsthand accounts healthy yellowheaded jawfish that were well established in tanks in a large marine fish breeding facility that died as a result of attempts to move them from one tank to another tank at the other end of the facility (presumably both tanks were on the same water system, so the problem was probably the stresses of capture and relocation)!

Jumping

By the way, regarding jumping....they certainly seem to have a lot of potential for jumping, and many folks report losses of jawfish due to jumping, though my experience has been that once the fish are esablished and comfortable in their burrows (and in a tank where they are not getting picked on), the probability of them jumping out is pretty low ...they stay by their burrows most of the time. Our tank is uncovered (though with 4" between the water line and top of the tank), but I'd think a good tight cover (with no openings along the edges or in the corners in particular) would be awfully important. This would be particularly important when the fish are first settling in, staking claims to territories, getting kicked out of burrows by other jawfish who are more aggressive and have taken a liking to the other fish's burrow locations, etc.

Though I think jawfish can be a little quirky sometimes, I also think they are absolutely wonderful fish. Of the fish in our reef and seagrass tanks, they are probably my favorite, and they attract more attention from students and visitors than anything else we have in our tanks.

I hope this helps.

Regarding my jawfish post from yesterday....

I mentioned that I had 3 that got along OK, and then when one died there was more serious aggression between the two remaining ones. It is conceivable that more intense aggression would have developed among the 3 anyway as they matured (???), even if all had lived. I really don't know, since I have not had long-term experience with a group or 3 mature fish. So don't necessarily take my last post as affirmation that 3 is a good group size to keep together. Another post in this thread a few days ago mentioned a tank with more (5 or 6 or so???...I forget exactly) in the same tank, and apparently these fish would spawn occassionally. Perhaps larger groups like this (in an appropriately sized tank) would be even better for spreading the aggression around??? (or, I could imagine that, depending on the particular dynamics of the tank, maybe more fish could in some cases exacerbate the stress levels from too much squabbling???....I really don't know). Certainly, groups of jawfish all popping their heads out of their burrows is a very cool thing to see, and also a larger group would give you a greater chance of ending up with at least one male and one female. I'd imagine that more than 3 would be fine in a 210 gallon tank.

By the way, one other jawfish hazard I forgot to mention For awhile when the jawfish were stressed out from aggresssion, I was tending to squirt food with a turkey baster right at their burrows to try to make sure all got enough to eat (they were getting a bit thin, weak, and ragged looking.....when getting picked on and ejected from their burrows on a regular basis by other jawfish or by other fish species, it seems jawfish health can decline really fast). This resulted in some food getting into their burrows, which attracted some of the really big scavenging fireworms we have in our system to take up residence in the jawfish burrows. This resulted in frequent contact between the fish and the worms, and the fish were often seen to have fireworm bristles sticking in their skin. This caused a fair bit of skin irritation, espeically in the head region, and between this and the aggression that was going on, one had a nasty infected operculum for awhile (this eventually healed). The fireworm bristles didn't kill any of the fish, but they certainly made me worry. We still have just as many big fireworms in the tank (probably more, in fact...there are LOTS), but I'm not directing food at the burrows quite so much, and we don't seem to be having this problem so much anymore.