The number of bettas that can be raised in a tank depends on the gender of the bettas, the size of the fish tank, and the breeding environment. Male bettas have a strong sense of territory, so it is not recommended to raise multiple male bettas in the same tank. It's best to keep just one male betta in a tank. If you want to raise a combination of one male and multiple females, it is advisable to have 2 - 3 females with 1 male, which can reduce fighting.

Breeding Recommendations in Different Situations
Tank Size: For small fish tanks (such as those less than 30 centimeters in length), it is recommended to keep only one betta. For medium-sized fish tanks (such as those between 50 and 70 centimeters in length), the number can be appropriately increased, but it should also be arranged reasonably according to the size and habits of the bettas.
Gender Combination: Male bettas have a strong sense of territory, so it is not recommended to raise multiple male bettas at the same time. A combination of one male and multiple females can reduce fighting. It is advisable to have 2 - 3 females with 1 male.
Water Quality Management: Good water quality management is very important for reducing fighting among bettas. Bettas like clear and clean water. It is necessary to regularly change the water in the fish tank and use a filter to help maintain the stability of the water quality.
Feeding Management: Reasonable feeding management also helps to reduce fighting among bettas. Betttas are carnivorous fish. Attention should be paid to feeding them an appropriate amount to avoid overfeeding, which may cause them to become more active and aggressive.
Shelter Setup: Setting up enough shelters in the fish tank, such as aquatic plants, stones, and caves, can give bettas places to hide and take cover, reducing direct contact and fighting.