My female Betta imbellis has been very lerthargic for the passt 4-5 days. She remains near the water surface, moving very little with fins partially clamped. Her colouration is pale, though there is no sign of external skin parasites. Gill movement is somewhat heavy and pronounced. Has not eaten for several days.

I'm suspecting internal parasites cos wild bettas are prone to them. What would anyone suggest as a possible problem and treatment?