Freshwater Piscine Diseases
There are many diseases threatening a hobbyist’s aquaria. Parasites and bacteria do especially well in this environment, for anywhere the parasite goes it will find a very moist, biomass-rich environment. The constant circulation of aquarium water and the stress of transport make propagation and infection very easy. Therefore, before adding any fish to an inhabited tank, quarantine is a very good idea if equipment (and patience) allows. At the very least, a thorough examination and quarantine of ANY suspect fish should be routine.
Common Diseases:
Velvet: A Dull Brown/Gray Fuzz Over a Betta's Body
Ich - Tiny White Dots on Your Fish's Skin
Fin Rot: Fins shrinking, becoming tattered, White rim on the edges of fins.
Septicemia: Internal Hemorrhaging
Flashing: A possible Non-disease cause
Simple, Broad-Spectrum Cures:
Using Garlic's Natural Defenses to Protect Your Fish
Peas: Cure for a Bunch-O-Things