In this article I will address the unfortunately very common myth of stress induced Betta Fish Tail biting.

I should noted that for decades this was considered a myth and proven to be just this, as all the scientific evidence showed that the causes of fin/tail damage in Bettas was due to:

• Injury from objects in the aquarium or tank mates
• Fin/tail infections, usually from Aeromonas
• Or the closest to being correct would be Bettas that are very aggressive, usually seeing their reflection in the glass of the aquarium or bowl. This however is NOT stress induced tail biting

Further References as per fin rot and Aeromonas:
*Fin & Tail Rot in Bettas & other Fish; Treatment and Prevention
*Fish Aeromonas & Vibrio Disease | Septicemia | Pop Eye | Treatment

Where did this myth get started?
Social Media influencers on YouTube and Facebook are the main source for this mis-information.
Unfortunately everyone who kept a few Betta fish suddenly became experts. Then search engines, especially Bings terrible AI project picked up these people stating this myth as it was repeated over and over and suddenly false information that is provably wrong has become the truth.

What is worthy of note is that while many now believe this myth/falsehood, it is on the side of those who are claiming it is true to prove a long established scientific fact that Bettas do not bite their tails out of stress, NOT the other way around [that is not how science works]

To be clear, it is stress induced tail biting we are talking about, NOT a Betta fish [usually male], seeing its reflection and thinking this is another betta fish and then attacking itself.
What is worthy of note is that cold blooded animals do NOT bite or chew themselves out of stress or boredom like warm blooded pets such as your pet bird, dog, or cat.

One point I will make that is an opinion as to how a lot of this got started, is that many Betta fish keepers try and attach human emotions, or at least emotions that their other warm blooded pets have, such as their cat or dog, to their finned cold blooded pet.
I understand the attachment many have to their Bettas and other fish, and most certainly individual fish have personalities, but that does not change the science that fish do not get bored or stressed to the point that they bite themselves.
Do fish get stressed? Of course, but this is more a programmed response such as hiding from aggressive tank mates or even lowered immune response. But this is not an emotional response in the same way we humans respond.

What is also worthy of note is that I and many other long time professionals in my field such as aquarium keeping guru Carl Strohmeyer, have yet to be provided clear evidence of Betta stress induced tail/fin biting. ALL VIDEOS PROVIDED TO DATE SHOW BETTA AGGRESSION as pointed out earlier.
Here is a video example of clear Betta aggression that is NOT stress induced tail biting:
YouTube; betta fish tail biting

Here is an excellent article that address this myth of stress induced betta tail biting in more depth, written by Steven Wright and Carl Strohmeyer:
The Myth of Stress Induced Betta Tail Biting

HERE IS AN EXCERPT FROM THE ABOVE CITED ARTICLE:
An interesting point that many of these non professional based blogs have in common is they state that certain bite shapes in tail damage are proof of biting when in fact this is simply more an indicator of the pathogen. The so called “Betta biting chunk” is typical of a Columnaris infection where by chunks of tissue simply fall off.
More common though of Betta Fin Rot is a more ragged deterioration which these blogs claim (correctly) is more from fin rot. Problem is Fin Rot is not a disease per say, rather symptom (just like Septicemia or so called Red Pest). This more ragged fin damage is more common of an Aeromonas or Pseudomonas infection.

Here is one of the copy & paste pictures that these blogs have shared that I have corrected to the correct diagnosis as per known science:

Of course one might ask what does it matter?
Why getting this right matters is such myths distract from the real causes and addressing these, especially if a case of fin rot is involved. This especially becomes critical when the fin rot is caused by Columnaris, albeit a less common cause of such damage, as Columnaris can be an aggressive infection if not addressed while the misled fish keeper attempts to address an incorrect cause.
Luckily often Columnaris is stress related, so the non experienced aquarium keeper removers the stressor and boom, they think they cured their Betta tail biting and the myth goes one!!