i agree that the stress is what's causing the issues. but most of the time the issue is going to be with shipping. most jawfish do not ship well, especially blue spot jawfish. you had success with your individual because you got it basically straight from the ocean. your fish didn't have to wait at an airport, be acclimated to an overstressed and chemically unbalanced fish store system, be handled by multiple collectors/wholesalers/lfs employees, or acclimate to multiple tanks over a short time frame.Just to point out-most diseases I've noticed are often brought about by an animal who's enduring stressed conditions. To point out that these guys suffer from a lot of diseases, but then say they don't need the DSB to provide them their deep burrows which they prefer, is somewhat contradictory. Give them their ideal habit, and perhaps they won't break down with diseases?
I purchased mine while I was manager at a LFS, got him straight from an importer who brought them across the border from the Sea of Cortez (as in I got him from the styro box that had just been driven across the border). Had him for 6 months before the tank crash, he was happy, healthy, and quite plump looking. Woud usually hang out fully exposed, but directly above his burrow and would dart back in immediatley.
Tank was a very light flow tank, had a CPR backpak and maybe one or two small powerheads and that was it.
i was saying the blue spots prefer a deep sand bed, but will adapt to the tank if a dsb isn't available. of course a tank without a dsb is not ideal for these fish, but that's probably not what's pushing these fish over the edge. bsj have been known to live on vertical rock walls in deep water as well, not just sand. the blue spot i had (prior to selling the tank and its contents) actually built a horizontal burrow even though the sand was quite deep. it would occasionally build a vertical burrow and even pile rock rubble around the opening, but it tended to do the typical goby thing and dig horizontal burrows or poke its head out from behind a rock.
here's my bsj in action (sorry for the crappy pics):



