The attrition of the cory fry has been slow but sure. I've lost at least one a day for the last few weeks, culminating yesterday in the first mass death-- about fourteen of them in one day. No major changes to anything except the regular water change-- it might have been the temperature shift (around five degrees, gradually) that did it.
The current population is still at least fifty, and some of them are really beginning to look like fish. A couple of the corpses couldn't be sucked up in a turkey baster, so that makes the death seem more "real" somehow.