sick male beta

Question
my son has a 90 gallon tank with 4 shabunkin goldfish and 5 large comet goldfish/he also has 1 mature male beta in the tank.the tank has been set up for at least 6 months like this.wayter temperature is 75 degrees/ammonia and nitritesand nitrates are normal...ph is 7.5       anyhow my son went away for 3 days and set his automatic fish feeder with small pellets and flake food(as ususal) when he got back today he noticed a small bulge in the rear lower abdomin of the beta...its about the size of a baby pea and bulges the skin equally on both sides of the beta. the beta swims normally and acts normally but there is a small amount of discoloration where the bump is. could this be a parasite or indigestion...we have isolated him in a 10 gallon tank and are treating him for parasites but I want to find out if that is correct or not. sincerely ken

Answer
Hello,
This could be the beginning of Swim Bladder Disease.  Swim Bladder is caused by poor diet, and overeating, which causes constipation.  A Betta should have 2-3 small meals a day.  Example:  2 pellets for one meal.  This is very hard to control if he is in with other fish.  Swim Bladder is curable when caught in the beginning.  Feed him a cooked frozen pea.  Remove the outer layer, and cut it into small pieces.  Try feeding this to your Betta one piece at a time.  This should make him waste, and he should have a pea every week on the day that he fasts.  Betta should fast one day a week, and have a varied diet on the other days.  For instance, he should have Betta Pellets, one day, Betta Flakes the next, Daphnia the next, Bloodworms etc...  The more you can vary his diet, the better he will be.  Always remember when feeding your Betta, that his tummy is the size of his eye.   He is a real glutton, and will do anything to get more.  Do not give into him, as this is the cause of many diseases.   If he is not swollen under his chin, that is where his tummy is, then it is not Swim Bladder.  
It could also be a tumor.  If this is a tumor, there is nothing you can do...Bettas live a long time with a tumor, if it is not cancerous.   Bumps, and Lumps are very hard to diagnose.  It could also be damage to one of his internal organs, and it could be flukes.
I'm sorry I cannot give you a straight answer, quite impossible..but the fact that he is still eating, and swimming normally is a good sign.  We will have to wait, and see if this lump gets bigger.
I would like to mention, that it is not good to put a Betta in with Goldfish.  A Betta is a tropical fish, and needs 80 degree temperature.   If you do bring up his temperature, do this very slowly, one degree every two days, as bringing up the temperature too fast could kill him.   Goldfish often have parasites that they can deal with, but not a tropical fish.  I would keep the Betta in the 10 gallon.  All you can do for him now, is keep his water very clean, and feed him sparingly.  Medicating is not good, as we do not know what is wrong with him.  Sometimes it is worse to medicate through guessing than to not medicate at all.
If his tummy is not swollen, you may add 2 teaspoons of diluted aquarium salt.   You may also add aquarisol to his water...making sure the other medicine is out.  Good old aquarisol has done wonders for me, and it helps fish with stress.
Hope he will feel better soon.
Lynda