Q: Can koi fish suffer from sunburn, and if so, how can I prevent it?
A: Koi fish do get sunburn. The typical symptom of sunburn is a red rash, and is particularly visible on white areas of the koi. The solution is simple – get adequate shade for the fish. This can be done by building a partial deck over the pond, or simply by adding big rocks that create shade and under which the koi can hide from the sun. Trees and plants also create shade, and so does umbrellas, if you need temporary shading.
Kevin Till, koi fish specialist