Does anyone know what this could possibly be? I noticed it 2 weeks ago and quarantined my fish for about 10 days. It didn't seem to get better or worse. Fish is eating and acting normal. So I put her back in the big tank (I've had tank for 5 years, no problems). 2 days later I noticed the white near tail. It looks like it goes straight thru the tail to the other side. The white sticking out near tail is exactly opposite on both sides of tail. Does not look like anchor worms to me.