I suspect it gets a little fuzzy. Many distinct species are rather similar, and those eating may not really know the difference. Morays, in particular, have terrible eyesight. On the other side, there is lots of evidence that some fishes will only eat those conspecific fish to whom they are not related.Thank you @tursiops The event I witness was also conspecific. One of my questions was whether this was always intra-species or also occurred between different species. The data from the article suggests that this is relatively uncommon. Have you ever witnessed this phenomenon?
Thank you @cgillis that, along with the reply by @waves_221 answers the question regarding intra and inter-species, which I assume would not be called cannibalism.