Silversides hurt fish?

[asylumdown]

I had my first unexplained fish death the other day. One of my 4 Bengali cardinals bit it for what to me seems no reason.

The only thing that I did differently immediately before it happened was finely chop up a silverside in to the food mix that I fed that day - I was trying to get more variety in everyone's diet. 30 minutes after feeding the cardinal was quite dead. No one else seemed bothered, my tank, to the naked eye, is completely disease and parasite free, every fish in there has been rigorously quarantined and treated for ich and other external parasites, and I haven't added any new fish in months. It was as healthy as the other three right before feeding, so I really don't know what else it could have been?

I haven't fed the silversides since, is it possible they were the culprit somehow? The do have tiny little bones in them so I was wondering if maybe she ate one and it damaged her insides?

[monocus]

sometimes fish just die-i don't think it's the food