I would think that a danio could out run an attack from a fancy tail guppy. Those huge tails kind of weigh them down some. I recently lost a fancy tail I had for about 2 years and he would kind of swim up to a platy and poke at him but not really nip. Just kind of bump his nose against him like a pesty little brother. I guess anything is possible though. Just keep an eye on him and check with your freind to see if there are any more deaths or injuries. Good luck.

Well see that's the thing no more deaths or injuries since she's moved it here. No deaths in my tank though...

I suppose it's possible but I just don't see how ;)

AS far as the danios dying, I am surprised - they are nearly indestructible! Definitely not the guppy that was the killer!

Possible territory issue??? When good guppies go bad?

i've had guppies b4 with other fish and if anything the other fish antaginized the fancys...so i dont think it was the guppies

A friend of mine had 10 gallons tank with only fancy male guppies. One day, he saw a goldfish that he wanted so badly and he brought it home. The next day or so, the goldfish died, which it was clearly attacked by the guppies. The point of the story, never underestimate the guppies. You know what people say, the fishes tend to be naughty (bad bahavior) when you are not watching.