Causes of Betta Fish's Abdominal Distension
There may be several reasons for betta fish's abdominal distension:
Contaminated Water Quality and Bacteria in Food: Poor water quality or bacteria in food can lead to internal bacterial diseases, resulting in abdominal distension.
Internal Parasites: Infection by internal parasites can also cause abdominal distension, and this situation is rather difficult to treat.
Inherent Defects: Similar to cancer in humans, this condition cannot be cured.

Treatment Methods for Betta Fish's Abdominal Distension
The methods for treating betta fish's abdominal distension include:
Medication: Methylene blue and coarse salt can be used, or Dr. T's Fungus Cure can be applied.
Antibiotics: Such as gentamicin and oxytetracycline, combined with magnesium salts or allicin for treatment.
Special Anti-parasite Medications: For internal parasite infections, Paraguard can be used.
Preventive Measures Against Betta Fish's Abdominal Distension
The preventive measures against betta fish's abdominal distension include:
Keeping Water Quality Clean: Regularly change the water to control the reproduction rate of bacteria.
Processing Feed: It's best to feed safe feed such as sterilized frozen bloodworms or brine shrimp.
Paying Attention to Feed Selection: Avoid feeding food that may carry bacteria.