I got up this morning to find my beautiful red mosiac cobra male guppy dead.
I had a trio in a 5 gal tank.
In the last week I had noticed one of my females being very nasty and chasing the other female away from the food. She is a big girl. The other female would go and hide under the weeds and was afraid to come out. She knew the bitch was serious.
I had never noticed her being aggressive towards the male.
Well I looked at him with a magnifing glass and could see some bad bruising on his bottom behind his head where I assume she hit him.
I have her in a breeder trap on the bottom of the tank.
Now the other female is coming out and swimming around.
I did get some babies from the 2 females and will have to wait and hope for another pretty male.
I sure wish I would have moved her sooner though. He was a gorgeous male.

I'm sorry about that. :(

I recently had to take my blue micky mouse platy back to the store for that very reason. She was nipping at the other girls so hard, they were actually rolling onto their backs from stress. Sometimes, you just get a really aggressive one...

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Creatures great and small, I love 'em all! But mainly the fish.

The exact same thing happened to me, but with mollies. The female killed the male, had to take her back to the store. Darn those female livebearers!

I think livebearers usually only 'kill' another fish when it's weak or compromised in some way, so if a fish gets bloat for example, the others will often attack it until it dies from shock.. A healthy fish should be strong enough to fight back, unless it physically cant get away if they're in a very small space, so my guess is there may have been something wrong with your male guppy, even if you couldn't see anything wrong with it.