multiple male bettas in one tank?!?!?!?

It's also important to keep in mind that splendens have been bred for finnage and color for many, many generations, with the result that the aggression is largely diminished. Certainly, some strains retain the aggression, and most will flare, but splendens are no longer the 'fighter' their wild cousins remain.

Still doesn't mean I would encourage people to put them together in smaller setups, but having the occassional tankmates get along is not unheard of, as long as you monitor and are able to seperate them.
 
I just added some guppies, yesterday,5 in with my male betta splendens. I had my doubts about this, and still am prepared to remove them, but he hasn't harrassed the guppies. My last betta , r.i.p, however didn't care for gups. who knows...

with bettas you never know.
 
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