Betta fish are known for their bright colors and unique personalities, but like all living creatures, they can be prone to certain diseases. Here are some common Betta diseases you should be aware of:

1. Fin rot: Fin rot is a bacterial infection that causes the fins of the fish to become frayed and discolored. It is usually caused by poor water conditions, such as dirty or overcrowded tanks.

2. Columnaris: Columnaris is a bacterial infection that causes ulcers on the skin and fins of fish. It is often caused by poor water conditions, such as high levels of ammonia or nitrite.

3. Ich: Ich (Ichthyophthirius multifiliis) is a parasitic infection that causes white spots on the skin and fins of the fish. It is most commonly caused by poor water conditions, such as high temperature or low oxygen levels.

4. Velvet: Velvet is a parasitic infection that causes a golden or yellow dust-like appearance on the skin and fins of the fish. It is usually caused by poor water conditions, such as high levels of ammonia or nitrite.

5. Swim bladder disease: Swim bladder disease is a condition that affects the fish's ability to swim properly. It can be caused by poor nutrition, genetics, or injuries.

6. Popeye: Popeye is a condition that causes the fish's eyes to bulge out. It can be caused by poor water conditions, bacterial infections, or physical trauma.

It's important to note that these diseases can be prevented by keeping the water clean and maintaining appropriate water temperature, pH levels, and oxygen levels. If you suspect your betta fish is sick, it's important to consult with a veterinarian or an experienced aquarist and to act as soon as possible.