He may just be a little bloated or constipated. Increase the frequency of your water changes. Clean, warm water and good nutrition are the best ways to keep them healthy.
Can you please fill out the form below so that we have more information? This will tell us things like the tank size, what he eats and how much, etc. Knowing this will allow people to give you better advice.
Answer what you can. Leave anything else blank.
What size is your tank?
What temperature is your tank?
Does your tank have a filter?
Does your tank have an air stone or other type of aeration?
Is your tank heated?
What tank mates does your betta fish live with?
What type of food do you feed your betta fish?
How often do you feed your betta fish?
How often do you perform a water change?
What percentage of the water do you change when you perform a water change?
What type of additives do you add to the water when you perform a water change?
Have you tested your water? If so, what are the following parameters?
Symptoms and Treatment
How has your betta fish's appearance changed?
How has your betta fish's behavior changed?
When did you start noticing the symptoms?
Have you started treating your fish? If so, how?
Does your fish have any history of being ill?
How old is your fish (approximately)?