yes it could be... sorry... i know sometimes a very strong healthy fish has been able to fight for his life for a long time.. before the parasites cause his demise.. i just hope now that any parasites don't attack your other healthy fish.... after this death i would treat the tank with higher heat and aquarium salt.. but some fish cannot take the salt.. mainly scaless fish such as clown loaches... etc.. so depending on what fish you have left.. or you could take the whole tank down and clean it and put them all in another tank from same water .. until the clean tank cycles.. but these parasites live on hosts and could be already doing their thing........ so it would be better if you could do the salt and heat. Just hard to tell you because it is all iffy now... some fish won't even be bothered by the parasite .. but my quess is that it is in the tank from feeders..
