Ick -This is the most scene or rather common parasitic disease among fish.  It is almost always present in freshwater aquariums and infects fish that are in poor health or have had a recent infection that has temporarily left them with a lower immune system. Ick can be visible on a fish if their natural resistance is weakened. Symptoms :  A fish that has contacted Ick will generally have a few small specks resembling the look of being sprinkled with salt.  The fish may scratch itself of tank walls or ornaments, show signs of rapid breathing, cloudy eyes, cloudy fins/ or some fin deterioration. Treatment : At the first signs of Ick, the fish should be treated in a separate tank if possible.  There are many items available on the market for the treatment of this such as Maracide, RidIch, and QuickCure.