Freshwater Fish Disease
This is on account of Nitrogen cycle being incomplete and the reasons could many, to name a few: overfeeding, overstocking of tanks, absence or inadequate functioning of filtration system etc. The symptoms are Red or inflamed gills, fish are gasping for air at the surface. This is common in new tank setup.
Fresh Water Fish Remedy
Ammonia poisoning is easily preventable. Avoid adding expensive and less hardy tropical fish until the aquarium has cycled. For more information on cycling your aquarium please read about the Aquarium Nitrogen Cycle. You can use a substance called zeolite to help absorb ammonia but the best solution is to ensure that your aquarium has cycled and that your tank is not overcrowded. If your tank has not yet completed the nitrogen cycle, you will need to perform frequent to keep the ammonia levels down.