I do not think the shark could leave those fins alone. Swordtails may be okay, but I am wondering if the "sword" won't be a problem with the Betta being after it as a "long fin" To be on the safe side i do not think i would try either fish, but my experience is limited in community tanks and I do not happen to believe that Bettas do well in them as a general rule. We may hear differing opinions from others.
Sharks are definately a no-no. Anyway they grow HUGE and would need a much bigger tank than I'm guessing you have your Betta in.
I wouldn't try a Swordtail either...the sword would be awfully tempting to the Betta. But also I've heard Swordtails can be quite aggressive and I wouldn't trust them with a Betta.
from what i have read about the sharks they are highly aggressive and will take out bettas..the comments about the fins is very accurate especially if ur betta is a male he will rip into just about anything with large fins like him....kinda makes u think he might have a complex doesn't it ?
Supposedly red tail sharks can be kept with bettas but I don't know about that one, they have a reputation for rasping their barbels against other fish sometimes.
Really, with bettas I would stick to peaceful fish that don't resemble the betta species. You can't go wrong with cories and otos. Iknow it's tempting but they don't seem to really be community fish. They aren't socialized to deal with other fish and they tend to be bad tempered with the fish that resemble them. They are not fighters except with themselves or the abovementioned though so more aggressive fast fish will make short work of them.
Well, first of all they were bred for like hundreds of years to be fighting fish. They had this awful sport where they'd put two males together and bet on which one would win the fight. So they bred them for this purpose to be aggressive. I can't seem to remember much about this so if anyone has anything to add or correct please do so.
The main factor though is the fact that they were isolated from the time they were determined to be males. They think that no fish are allowed to be with them, and they don't know how to handle other fish. They have been, if you will, socially deprived.
And then there's the fact that Bettas are just a more territorial species, for whatever reason. They may mistake other fish with big fins (like Guppies) for another Betta and attack them as such.
I believe that before they were selectively bred they were still already highly territorial. And just as an added note they still breed and fight bettas in thailand. I was reading this article once (I'll see if I can find it) where it talks about how there is like a whole training regimen and diet and everything for these bettas. And supposedly the fights are more ritualized. There is a little fin nipping, but because the fins are shorter and stronger then the bettas we keep supposedly it is not so bad. And they dont attack each other when they go up for air. I'll see if I can find that article again.
There's like a billion articles on fighting bettas if you google it but I cant find the one that Im talking about.