lump on fish belly

Question
My daughter has a white mountain minnow in a 2 gallon
tank.  The minnow shares the tank with a goldfish.
We have an aerating filter only and change 50% of the
water every week.

Last night my daughter fed the fish blood worms and this
morning the white mountain minnow has a large lump on its
belly.

Might this just be a digestive problem or do you think it
may have an infection?

Thank you for your help.

Answer
Hi Richard;

Since it happened overnight it could just be constipation. Fish often overeat on their favorite tasty foods. I would "fast" them for two or three days to help the digestion clear.  No food at all for that time. Then, feed cooked, peeled green peas in little chunks for two or three days after that. No other foods, just the peas. It's very good for the goldfish too. They need veggies for their digestion.

Something you may not know about is the size tank your goldfish needs. Goldfish get really large, 6 to 8 inches long and are very messy guys. They need at least a ten gallon tank just for one fish, with a power filter to handle their waste. Your little minnow is in danger of being eaten too as the goldfish grows. Any fish with a mouth big enough will eat another fish, it's just nature. The best situation for both your little fellas would be to get a ten gallon or larger for the goldie and keep the small tank for the minnow. Then get the minnow two more of the same kind to pal around with. White Cloud Mountain Minnows are schoolers so they should be in groups.  Here are pages about both types of fish;

http://www.firsttankguide.net/goldfish.php

http://www.fishprofiles.com/files/profiles/447.htm

Have fun and I hope all goes well!

At Your Service;
Chris Robbins