It is most likely that the food you are feeding it with, has red dye in it.
Possibly feces?
Long, stringy feces can be a clue in informing you that your goldfish has constipation. You can know this when the feces do not fall from the fish right away. To cure this, I suggest that you feed the goldfish the insides of boiled frozen peas for a few days. Eating too many fish food that are full of protein can be the result of constipation, like pellets.
if your goldfish lives in you then yes
A goldfish with a red head has a distinct coloration that sets it apart from other goldfish. The red head is a unique feature that makes it easily recognizable.
All goldfish are freshwater.
No, goldfish should only live with goldfish with a few small exceptions that do not include red ear sliders.
The red food coloring in (mostly cheap) red wine combined with the normal brown color of feces = green!
it was blood
The food you ate.
a goldfish
because they are sick dummy
Many colors. I had two male goldfish. One was white and the other one was red.