Petco's Betta Care Sheet lists loss of color or appetite, spots or fungus on the body or mouth, listlessness, and labored breathing as major red flags to watch out for. The care sheet suggests testing the water quality of the betta’s environment if any of these symptoms are present.
Dr. Audrey Harvey at The Courier Mail confirms that loss of appetite, dull color, clumped fins and buoyancy problems are signs of health issues. Petsmart adds unusual swimming patterns, thinness, abdominal swelling, inflamed skin, clamped fins, and scraping body on rocks as symptoms to watch for and suggests speaking to a veterinarian if any of these signs are observed.
Two health issues common with betta fish are fin rot and ich. Fin rot is characterized by fins that appear frayed or disintegrated and are red at the base. A betta has likely developed ich when white spots appear on its fins and body and cause it to rub against objects in its environment or swim awkwardly, notes Petco.
Dr. Harvey notes that many common fish diseases are treatable. She suggests consulting an expert if any of these symptoms are observed. Petco also encourages speaking to a veterinarian for advice on appropriate treatment when any of these signs of health issues are present.