Betta Fish can become sick from many different situations. If the water is too warm or too cold, it can severely affected them. Perhaps there is chlorine in the aquarium water or another chemical, that is toxic to your betta caused by various catalysts within the aquarium.
The most common cause of constipation in Bettas is overfeeding. The symptoms of Constipation are bloated stomach, won't eat, lack of defecation. Due to their high protein diet with little fibre, constipation in Betta fish is common but also very curable. It is important to treat constipation as soon as possible to avoid more serious problems with your Betta.
Fungal infection is a common disease in tropical fish. Poor water quality can cause increased fungal infections on fish in the tank. The affected Betta usually has cotton-like growths on their skin. The sickness of fungal infections can become fatal if it is not treated early enough.
Fin and Tail Rot
Fin and Tail Rot occurs when the Betta is distressed due to poor water conditions, overfeeding, uneaten food, overcrowding or rough handling. One of the earliest symptoms is ragged fins. As the disease progresses, the fins become increasingly shorter and some whiteness appears on the edges. Fin and Tail Rot can be treated by medications containing antibiotics.
Ich or White Spot
Ich or also known as White Spot is present in the majority of fish tanks and aquariums although healthy Betta fish have natural immunity to it. Ich caused by a parasite (ichthyopthirius) that uses the Betta as its host. Ich is easily identified with small white dots on the body and fins and in some cases the eyes. Salt baths are useful treatment for Betta with ichthyopthirius parasite.
Slime disease is common disease to a Betta fish caused by three different parasites (Costia, Cyclochaeta, and Chilodonella). Slime disease weakens the Bettas immune system which makes them more prone to getting a secondary illness or disease. This parasitic disease is characterised by an over production of mucus coating. Because of increased mucus production, affected fish often show signs of respiratory distress such as heavy or labored breathing.
Velvet is common among Betta fish and comes in the form of a parasite (adult Oodinium) that attach themselves to the Betta fish. The symptoms can be easily identified with a goldish-yellow colored dust like appearance on Bettas body and fins. Bettas with velvet will dart around the tank looking for spots to rub themselves on (just like Ich) in an attempt to get the parasites off. If left untreated, Velvet can lead to death.