All right. I may as well show what happened, perhaps someone else will be helped by ID'ing this crap faster.
First, the picture:
This has been taken shortly after the death. Because of water reflection, the image is slighly distorted (the aspect ratio is off). The sores, unfortunately, are much more visible than an hour early, when the fish was still alive. While the fish was alive the sores did not appear to be very deep.
In addition to the sores, you can see some anal discharge, which does not look healthy; the sores themselves are actually quite deep and represent the points where the nematodes broke through the skin. Naturally, in addition to the skin damage there is likely a lot of internal damage one cannot see here.
I killed the fish by hitting it with levamisole the moment I saw the sores; while the diagnosis was not conclusive (thus my uncertain original post), this possibility had to be covered immediately. (Usually I'd wait with levamisole 24 hours to let the fish adjust to the new tank). In a very similar situation in the past I had a kuhli with similar, albeit less extensive, nematodic damage; I managed to keep him alive (still is, and still has a large scar). Very likely what happened to the
Nemacheilus is that dying worm<s> pierced the vitals and killed it quickly; this happens because levamisole makes nematodes very active just before it kills them.
Anyway, those who asked about levamisole killing fish: here is the case when this happened. The fish was doomed, but probably would have lasted a couple more days without treatment.
This is the second time I see this type of infection in hillstreams; first it was in lizard-type loaches from HK, now it is in
Nemacheilus from either Thailand or Singapore (unsure right now which). So this is common and if you are into hillstreams, it may be coming your way too. Naturally, this is much more serious than CWS; if untreated this is certain to kill at least all the bottom fish in the tank, and possibly all fish in all your tanks.
Notice also that 2-weeks quarantine is useless with these worms. Their livecycle is long enough that both times I've seen this, the problems came up around day 20. For example, this
Nemacheilus had more than two weeks of quarantine at the store. Other useless things are:
* relying on examining the underside (most fish will not have such sores, and they appear only when the fish is *very* infected; smaller hillstreams are likely to die before sores appear) -- but it was still a bad error on my part not to do it.
* drugs other than levamisole; PraziPro, for example, was tried and failed the last time I encountered these worms.
Well, I guess that the new schisturas will be getting several levamisole rounds now, even if they are probably not infected. I'll make it up to them with bloodworms, they were living on algae wafers for a year.... hopefully they still remember that there are better foods available.
Hope this is of use to someone.
)