What if a betta fish has a red bruise in the middle of its stomach?

If you know it is a bruise and how the fish got bruised just make sure the fish is looked after properly and it should recover OK. If on the other hand you only "think" the fish is bruised because you can see a red blemish around its stomach area. Then follow the rules below because you are doing something wrong. The basic rules for successfull fishkeeping are :- 1 inch of fish needs at least 1 gallon of water.(A Betta is a 3 inch fish) :- Every tank needs a permanently running cycled filter. :- Every tank needs to have 50% of its water replaced every week. The aforementioned are absolute neccessities if you wish to keep fish alive and healthy for any length of time, as is the knowledge of any special requirements for the species of fish you wish to keep. (A Betta needs to be kept at around 78F)