ok normally swordtails are not predatory fish and are not agressive since i kept 6 in a comunity tank from when I was 3-to 10 years when i moved to canada.
since i started keeping fish again in 2002 my 1st fish were a pair of red swords since they were the only ones I knew of the fish I saw and were completely healthy. The male died in 2004 because of a biserk tiger barb which was less then an inch yet killed...
-1 male swordtail
-2 rosy barbs
-2 other tiger barbs
-2 female and 1 male guppy
all in one day while i was at school...
as soon as i got home it was finishing off one of the rosy barbs... the other ones were all befined and eyeless mostly
he was only fish left in aquarium except for the red female swordtail which kept its ground :crazy: :crazy:
anyways

the female swordtail is still alive and doing well. Got atacked by fungus but coppersafe saved her.
heres the deal why this swordtail
this fish will kill anything and i mean anything
you might find this hard to beleive but after she killed my oranda, i got a bet with my friend that my swordtail could crush his beta. He was like ye right. we bet 20 bucks and put the fish together in a 10 galon tank. after about 2 mins they were going at it...
and amazingly my swordtail lost a piece of fin which grew back while the beta got completely aniahlated
this fish now chases 1.5 inch rosy barbs and thats 4 of them
its not teritorial i can tell you thatt much
any ideas why this fish is so insane???
like seriously i am willing to do the beta experiment one more time if u want to see it
il even record it and take pics
i have never seen anything like this in my life :wtf:

I had a male swordtail and he was perfect. I had an aggressive Chinese Algae Eater that harassed my tropical tank, then when I moved him to the goldfish tank he did the same. My co-worker needed an algae eater so I gave it away to her. She told me that her swordtail constantly picks at it and one day the algae eater was near death with large bloody welts on his stomach from the swordtail biting it. I guess u just get that certain fish that stands out and doesn't fit the profile.

interesting...
it killed another beta but my batteries died so now i have no pics...
this time its missing a bit of its tail
im seriously confuzed by this fish :crazy:

Maybe you should put him into "solitary confinement" for a while and see if his attitude changes. :laugh: