I have a 20 gal long with some peaceful community fish and I’m currently keeping a male and female in separate tanks. I’d like to add them both to this one tank but don’t know how they will react in the same tank. Is it safe to house them together?
A: Generally speaking it isn’t a good idea to house male and female Betta splendens in the same aquarium. Both sexes are capable of serious aggression. Most commonly, males will harass females if perceived to be in their territory but I have also bared witness to a female killing a male brutally after crossing a tank divider. This is not to say it is impossible in a 20 gallon tank. In a tank that is this size or larger you may be able to have a pair of bettas set up separate territories provided the following:
1. Their individual personalities are relaxed or submissive. Individual Bettas, both males and females, have unique personalities. Some are highly territorial while others are more complacent. If you have had your bettas for some time and have come to understand they are gentler (well, as gentle as Fighting Fish can be) then you may consider housing them together.
2. The tank set-up should be conducive to housing both fish. A more horizontal tank, like your 20 gallon/long, is appropriate. There should be calmer, current-free water on either side making each far end inviting for the bettas. Try placing the HOB filter in the middle as an invisible barrier between the sides. Lots of hiding spots and heavy plant material will help to block sightlines from one Betta to the other. Less contact is better.
3. Provide ample time for observation. If you are a Monday-Friday worker, try acclimating them to their new tank on a Saturday morning and continue to monitor them carefully all weekend. Dropping them in and going to work could leave you with one or two dead bettas when you return. Also, have a Plan B. Plan B would include keeping their old tanks up and running in case you need to separate them again and having some antiseptic fish medication like BettaFix or Melafix on hand to apply to injured bettas.
Housing a male and female together could prove to be very interesting and you may even get to observe their courting behavior, however, their is significant risk for injury or even death. I would recommend exercising extreme caution and remember that an aquarium is not a truly natural environment. You are responsible for their wellbeing.