wild-caught fish

[anggrek@juno.com (Tsuh Yang Chen)]

there was a recent thread about wild-caught fish in this list.  i have
noticed that many of the wild-caught fish from south america tend to live
in your tanks or at the shop for several weeks but inevitably waste away.
 i wonder if this is due to the fish's inability to adapt to a new
environment and new food, or other causes.  

i recently found my mystery trumpet-nose marbled knifefish dead.  this
unidentified gymnotoid had lived in my 55 gallon for about 4 months.  its
body shows no sign of disease or starvation.  it obviously did eat
something while there otherwise it wouldn't have lasted this long.  the
tank in question is very stable, heavily planted and houses nannacara
anomala, apisto nijsseni, catfish and tetras.

any thoughts on the subject would be appreciated.

tsuh yang chen, new york city