I am keeping male and female bettas together. My experience.
Recently, I made the choice to put my male betta and 2 females into my 4,160 liters (1,099 gallon) pond.
It was risky, but I wanted to see how they would react to the large space and their "natural" environment.
They are in their with many goldfish and guppies.
They have been in for over a week, they all have no nips or injuries on their fins.
I have witnessed the male and females all school together, they eat together. There is no violence. The male is very protective over his females. He will flare at my goldfish and shubunkins if they come too close.
In winter I will be moving the trio to my 55 gallon and see how it goes.
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