What causes koi to shed scales?

Koi can shed scales due to various factors, including diseases, parasites, and environmental stress. Conditions like bacterial infections, fungal infections, and infestations by parasites such as anchor worms can damage the skin and lead to scale loss. Additionally, sudden changes in water quality or temperature can stress the fish, exacerbating scale shedding. Proper care, including maintaining optimal water conditions and monitoring for signs of illness, can help prevent scale loss in koi.