Answer: Yes, they do—especially between male bettas of the same species. Their fights can be extremely intense and even fatal.
1. Main Reasons Betta Fish Fight
Territorial Instinct: Wild bettas defend their active range, and this behavior remains intact even in captive environments.
Male Competition: When two male bettas encounter each other, they will fight for dominance through fin-flaring, biting, and other aggressive actions.
Increased Aggression During Breeding Season: Male bettas in mating season may attack other fish—even females. Females must be separated immediately after mating.
2. Which Betta Fish Are Prone to Fighting?
Males of the Same Species: Fights are inevitable between two Siamese fighting fish (Betta splendens) or two paradise fish (Macropodus opercularis), for example.
Females of the Same Species: Female bettas (such as "Plakat" females) may also fight, but the intensity is usually milder.
Different Species: Conflicts between bettas and other fish species often stem from territorial disputes or provocation (e.g., fights with long-finned fish).
3. How to Prevent Betta Fish from Fighting?
Solitary Housing: The safest method, especially for adult male bettas.
Separate Tanks or Dividers: If you need to keep multiple bettas, use a clear divider to separate them and avoid direct contact.
Enriched Environment: Add aquatic plants, caves, and other hiding spots to reduce territorial competition.
4. Post-Fight Care
Isolate Injured Fish: Prevent further attacks or infection from other tank inhabitants.
Treat Wounds: Use methylene blue or yellow powder (sulfanilamide powder) for medicinal baths to prevent bacterial infections.
Monitor Behavior: If the fish continues to refuse food or stays at the bottom of the tank, further inspection is required.
5. Notes on Special Cases
Juvenile Stage: Baby bettas may coexist peacefully for a short time, but they will start fighting once they reach sexual maturity (around 3 months old).
Female Community Tanks: A "sorority" of 5 or more female bettas is recommended to spread out aggressive behavior. However, close observation is still necessary.
Summary
Fighting is an instinctive behavior for betta fish, especially among males. It is advisable to reduce conflicts through isolation or environmental management. If community housing fails, separate the fish into individual tanks promptly.