Betta Fish: About “testing” bettas for tankmates with a mirror and shrimp

Here's my very angry, but otherwise lovely red plakat Dante hating himself in the mirror and eating shrimp, while still existing peacefully with strawberries and the same shrimp he snacks on.

You cannot test a betta's temperament/compatibility with other fish by showing it another betta/mirror or food(shrimp) and expecting it to be chill with it. I see this suggestion thrown around all the time to walk around the shop with a mirror and see how the betta reacts, or to try them out with shrimp. Moreover, you can't properly judge an animal's temperament if they are all kept in a tiny crappy setup (cups, mostly, from what i see here) and stressed to hell as it is even without you carrying them around and showing them different fish to "test" them. Hell, mine will nip at the bag if im floating new fish in it. I have another video somewhere from before when I showed my alien some bettas from the coccina complex. He immediately recognised them as bettas (in spite of their very different color and shape, which is very interesting i think!!) and flared like hell at them, while coexisting peacefully with chilis, danios, corydoras, loaches, etc. He eats shrimp too!

What I'm trying to say is, tankmates are always going to be a hit or miss and it's on you to make sure you have a backup plan in place to sort it out if it falls through. Sometimes it's swapping fish around/setting up a new tank, and sometimes it's returning the fish back to the shop (or rehoming, whatever). Just because your betta was the chillest or angriest in the shop doesn't guarantee success or failure. Personalities also change as they mature and relax more in the new home, which also doesn't necessarily mean the fish will chill out with time or become more aggressive.

Your best bet is setting up an environment with all the fish (or shrimp! Shrimp matter too) in mind, not just the betta!!! Make sure everyone has appropriate numbers and the appropriate environment to thrive in so they don't feel like they have to nip or chase everyone. And even then, that's all we can do to hopefully make it work, and unfortunately it's still no guarantee and you can end up with a particularly angry individual.

We have been lucky enough that all our bettas so far have worked out wonderfully with other fish, but who is to say that Dante won't one day wake up and decide he'd rather live on his own? And if that day comes, we have other tanks we can swap him to to keep everyone happy and safe. 🙂