I don't think they are toxic. I mean any remains of a dead animal in your tank will pollute your water, but nothing toxic with the mandarin. I had my mandarin eaten by my haddoni.
Sorry to hear that, mandarins can be tricky. was it eating?
Dans haddoni ate almost ALL of my fish! mandarin, lawn mower, anthias....needless to say, that's why it's Dans haddoni now lol