Yes I did feed guppies to my N.bical and N. ventricosa. Last summer I bought some guppies to live in my rain barrels. I put four guppies in each 55 gallon barrel. Next thing I knew I had hundreds of guppies. So I took some out and put them in a hugh sink I had. Some of those died. One of the guppies was pretty big, so I put it in my biggest N.bical pitcher. I put two medium sized guppies in two smaller pitchers of the bical. I had two tiny guppies so I put them in my N. ventricosa pitchers. The next day one of the bical pitchers started turning brown. Within a week all the pitchers with guppies was turning brown. After the pitchers have completely died I cut them off and I looked in side for the fish and there was no sign of the fish at all, even the bones were gone.
After thinking about it for a while, whatever killed the guppies may have killed the pitchers.