Anchor Worms like fish lice are not microscopic and will attack healthy koi. They crawl under a scale and attach themselves to the dermis layer. As they grow a “Y” shaped body emerges out from the beneath scale upto 1 inch long. This “Y” shaped body is actually two egg sacks containing up to 700 eggs. The problem, again, is not the stress it might put on the fish as much as the chances of starting a bacterial infection in the area of attachment.