Okay, so i'm in Dr. Tahl mode - let's review the situation...
everything fine fine fine (did tests about a week ago with same results as always) until the temp goes in less than 24 hours from 78 to 84... I'm thinking the time of the fluctuation was probably more like 6 hours from 78 to 84 - keeping in mind that it's only 55 gallons, so changes can happen pretty fast...
now, the only one to suffer is the blenny... strange, but maybe not - maybe he's the most fragile fish in my system? Gotta check that out. He was certainly the youngest (at a year and a half...) but that means nothing, most likely...
He loses all color, gets totally calm (not his style) and is dead in two days with no visible signs of illness whatsoever. I am ruling out parasitic attack right now. When I took him out, his skin was in tact, eyes were pretty clear (he must have been dead for only a very short time...) fins were in tact... there was no deterioriation whatsoever on external inspection. (I ~did~ check to make sure he was dead)
Now, of all the fish in my system, he was the most active, so it is quite possible that his O2 requirement was greater than that of all the other animals in the tank. And his behavior is congruous with lack of O2 - lethargy.
what about the dull color? A possible symptom of lack of O2? It is possible. I know that when we lack O2, we become pale - it is reasonable that the same should happen in a fish. If this is the case, then on post-mortem inspection, i would have been able to tell by the color of his gills whether or not he was lack oxygen, except that when he died, the temperature in the tank had already come down, the lack oxygen would have been relieved, and he would have had nice looking gills -
unless he was suffering ischemic reperfusion damage, which is, I think, also possible... let's say he was lack oxygen for a time, and then he was exposed to oxygen. oxygen is actually damaging at high levels to tissue, and it is possible (and here i hope there is someone who can attest to this or tell me that I'm remembering things wrong - it's been a while since i was a biochemist...) that what killed him was not the lack oxygen, but the return to a normal oxygen level.... In which case, maybe his gill tissue would show O2 damage...
the thing is that I have never autopsied a fish before (I've done horses, but they don't have gills...), and I don't know what to look for....
so i do think that the sudden rise (and subsequent drop) in temp is what did him in, but it was not the heat that killed him, but probably the change in O2 levels.
consensus?