your fish is sick.... when goldfish get red streaks of blood in their fins its a sign of several posible types of illness... watch out he may fade away.
I didn't really know that. Glad you told me. I had that kind of fish, but had to look at photos on Google to paint it. Seemed all the fish had some veins in their tail. Ewww. I won't paint them in again. Shhhh don't tell anyone! : )