There are several possibilities. It could be environmental. Check for the following:
- Sharp decor
- Plastic plants
- Sharp rocks
- Heavy filter suction
- Aggressive tankmates
- Check the water quality
No one knows why Bettas bite their own tails. Some people say it’s stress, others say boredom and still others think it could be hunger, pent up aggression or even hereditary. I read an article on ultimatebettas.com that states that there may even be something outside the aquarium stressing our fishy friends out. Think about your habits which occur just before you notice tail biting. Is loud music being played? Are there alot of people in the room near his tank? Even though the possibilities for cause are endless, we do have ways of helping our Bettas through this issue.
If all water perameters are not at 0 ppm when you test, make sure you do a big water change. Next, add some stress coat to the water to help his injuries heal. Continue daily water changes to avoid infection. I have read that some Betta keepers have successfully stopped tail biting by changing the aquarium decor around or by adding more silk or live plants. You could also try moving the tank to a new location or the fish to a new tank. It is wise to try to lower light levels by adding floating plants or getting a dimmer bulb for your fixture. This cuts down on the reflection your Betta may see and may reduce aggression. If your fish tank is big enough you could try adding some fast swimming peaceful fish to redirect any aggression from your Bettas tail to other fish. Of course with any treatment having to do with trial and error, you should only try these things one at a time so that you can isolate the trigger or cause of the behavior.
I know it's tempting since his tail is already mangled, but if you are a breeder, it is extremely unwise to breed a Betta fish who exhibits tail biting behavior. You certainly don't want to get a reputation for selling tail biters. Also, if you are breeding, you should be doing so for the express purpose of furthering the hobby and producing the best fish possible. This committment means not only perfect form and color, but also having consideration for temperment and aggression of the fish you breed.
Below is a video of a Betta caught in the act of tail biting. You'll notice he flares at his reflection alot and swims in tight circles trying to grab a bite of his tail. I hope the preceeding advice helps anyone struggling with this issue. If anyone has had experience with this problem and would like to share what has worked for you, please feel free to leave a comment below. We would all love to hear your story.