I have a betta in my community tank with std n black neon, cardinal, black phantom,Ram, otto, cherry bard n shrimp. Everything when very well last 3 months, until i introduce a female betta into the tank last week.
The male start to make bubble nest and the betta spawn. Then the male when into protective mode n attack any fish that swim within 20cm from the nest inc otto.
I found the female was dead on monday. Then on tuesday, i saw a fully grown black neon lying restless on the leaf which i though maybe its time is up or some kind of internal infection.
n I though the male betta just chase the others until the male kill the black neon right in front my eye.
I notice it REALLY bite the fish that come near to the nest. As the bitten fish became weak n slow, the male betta will continue to pick that particular fish till the fish beyond recover.
Probabily the female betta was kill by the male betta too...
Btw, I have remove the betta and hatched fries to separate container.
I tried to reintroduce the male betta back to the main tank last nite but it still attacking others.
HTH