There's a lot of information out there on Koi fish. Here are a just a few fun facts that you might not know! When consulting an expert, make sure you're talking to someone who is familiar with the location in which you live!
Koi fish are sensitive to the sun. They may get sunburned if they live in ponds that do not provide enough shadow and shade for them to escape to. This kind of shade can be provided by either external elements, such as trees, bushes, or shade sails, or from within the pond, like as lily pads, marginal plants, and well-positioned rocks and Koi caves.
Koi fish release ammonia into the water. When a large number of Koi inhabit the same pond, levels of ammonia can increase rapidly and induce poisoning of the fish, especially if it’s not an ecosystem environment. Although life in a community can be dangerous, Koi fish enjoy the company of other Koi fish. It’s a good idea to consult an expert to see how many Koi are right for your size and type of pond before adding them.
During the mating season, females produce thousands of eggs that will be fertilized by the male's sperm in the water. Only 50% of fertilized eggs will survive. This explains the “foaming” and “fishy smell” that is sometimes present in the pond, particularly in the Spring.
Koi fish can mate with goldfish because they are closely related; however, the result is sterile offspring.