My Reflections on Mahachaiensis

In recent years, more and more captive‑bred Betta mahachaiensis show a slightly pointed tail, almost resembling a mild spadetail. Many people assume this is a genetic trait or even a new “variant”, but the explanation is much simpler and has to do with how these fish grow in captivity.
After more than ten years of breeding mahachaiensis, I’ve observed a consistent pattern: during the first 2–3 months of life, juveniles are extremely shy and highly sensitive to stress. It takes very little to trigger a defensive response—sudden movements, reflections on the glass, the presence of other males, water changes, bright lights, handling. When they feel threatened, they instinctively close the caudal fin into a sharp, needle‑like shape, adopting a classic defensive posture.
This repeated posture has a direct effect on the development of the caudal rays: the central rays are compressed and stimulated more often the lateral rays remain less extended over time, this leads to differential growth, producing the slightly pointed tail seen in many captive fish
In captivity this happens far more frequently than in the wild.
A captive mahachaiensis, even with the best care, experiences stress for a large portion of the day: smaller tanks, reflections, noise, other fish in sight, frequent maintenance, artificial lighting, and the lack of dense natural vegetation. In the wild, by contrast, the fish live in environments full of hiding places, with much lower population density and far fewer prolonged stress events.
This is why wild‑caught mahachaiensis almost never show a pointed tail: their growth takes place in a stable environment, rich in cover and with minimal chronic stress. The caudal fin develops evenly, without the difference between central and lateral rays that we see in captive‑bred individuals.
In conclusion, the slightly pointed tail seen in many captive mahachaiensis is not a genetic trait, but the result of a combination of: chronic stress during early development repeated defensive posture differential growth of the caudal rays
It’s a clear example of how the phenotypic plasticity of Betta species can alter morphology even without any genetic mutation.
And it explains why wild fish, raised in their natural habitat, maintain a more balanced caudal shape without this characteristic. What do the many experts in this group think about these reflections of mine.