hi,
You have gotten some pretty good answers here so far, but just wanted to add to this..
My fiance has a 10 gallon nano-reef with 3 yellowheads in it. They are quite fascinating. I would highly recomend them to anyone and everyone, simply for the enjoyment of watching their quirky behavior. Jawfish are very gregarious, and will live in small communities, and are seldom too "crowded" as they burrow and live in these burrows. They can be kept singly, or in groups, either way. They like a deep sand bed (on the order of 6"-8") that is varied in grain size. One of the most important things to give them is some reef rubble. Jenny (my finace) recently added a bag of small shells that we picked up in the keys last month..the jaw's love it. It gives them something to use to support their burrows. They drag the shells around the tank constantly and are always working to improve their homes. While the jaw's will definately cause some minor problems with a denitrifying sandbed, they are only minor problems. They tend to make a single hole to scoot into, not an extensive tunnel network like some gobies, so the lack of denitrification will be localized. Also, they are not sand "sifters" as they do not eat the microfauna that grows in the sand bed, prefering to simply "move" sand by the mouthful. They feed fairly regularly, and the 3 we have now are eating formula II, prime reef, and frozen brine. If you decide to go with a jawfish, you will have a very hardy fish, that is very resilient, and has very few problems with diseases. They are hardy, but beware, they dont like the company of wrasses, tangs, and other fast moving, daring, flashy fish... they will keep the jaw's stressed out and they will stay in their hole. The yellowheaded jawfish comes from the caribean, so collection is generally not a problem, and they are almost never the victim of cyanide poisioning.
sorry this is kinda jumbled up, I dont have lots of time to write it all up nicely, but wanted to give you all the info...
vigg aka goby.
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