I have a 4" mostly white goldfish (among others). I noticed yesterday what looks like steaks of blood in it's tail, back and fins. Anyone know anything about this?? It still seems to be normally active.
They do have a tendency to change colors some over the course of their lives, but I would have to know more about the breed of goldfish as well as your water parameters to answer the question fully.
Red streaks in in tail and fins of goldfish is usually a condition that develops because of high nitrate in the water. I would suggest that you check what your nitrate reading is.