So you think fish don’t need protection from the sun simply because they are always “submerged” in water, right? Well, perhaps you don’t know that Koi can get “sunburned”. That’s right; some varieties of Koi tend to loiter close to the surface of the pond or in shallow areas, and that leaves their backs very close to the surface of the water or, at times, even partially out of the water.
Provide a shaded place on the pond, especially during the midday and early afternoon. A Pergola, shade net, or reed mats will do the trick. Of course, you should also employ floating plants in your pond or use some specially-designed pond salts which will improve the slimy coat on your fish and also improve their gill’s function, which protects them from illness and exposure to the elements.
Nowadays, there also are some commercially-available “pond dyes” or “pond tints” which can be helpful for that purpose.