Article in English: When a betta gets sick, his coloring may look faded out. He may even lose his color altogether. In a healthy betta, its fins will be whole. An unhealthy betta may develop holes or rips in its fins. Another unhealthy sign is if your betta's fins appear clamped down to the body; that is, they aren't fanned out properly. If your betta is sick, his activity level will go down. He won't be his normal, active self. His movements will slow down some.  Another sign of sickness is your fish hiding out at the bottom of the tank more often than normal.  Lethargy can be caused by low or too high temperatures as well, so make sure the temperature range of the water is good. With some sicknesses, your fish may stop eating altogether. If your betta appears uninterested in food, he could be sick. Look for small, white spots, especially around the head and mouth. This symptom can be a sign of a certain type of parasite, called Ich. It may sound funny to check a fish for breathing problems. However, if your betta is constantly at the top of the tank trying to get more air, that is likely a sign of a problem. Bettas naturally go to the top of the tank to take a breather at times, but doing it frequently is not okay. If your betta is trying to rub against the side of the tank, that could be a sign of a problem. Similarly, if your betta is trying to scratch on plants or objects in the tank, he might also be sick. Bulging eyes can be a sign of sickness. Watch for your betta's eyes protruding from its head.  Raised scales can also be a symptom of sickness.  Watch his gills. If he's unable to close his gills, they may be swollen, another sign of sickness.

Summary in Vietnamese:
Quan sát hiện tượng cá bị bạc màu. Để ý đến vây cá. Quan sát bộ dạng lờ đờ của cá. Chú ý đến thói quen ăn của cá betta. Kiểm tra các vết đốm. Phát hiện các về đề hô hấp ở cá. Quan sát hành vi cọ hoặc gãi của cá. Tìm các triệu chứng thể chất khác.