Koi fish are a species of carp. The phrase “mongrel koi” refers to koi fish that have interbred with other fish species. Koi fish are popular in fish ponds due to their vibrant colours and streamlined appearance.
Koi inhabit koi ponds as ornamental fish used to beautify gardens and outdoor areas. There is no such thing as a mongrel koi; the word is used ironically to refer to the unknown lineage of koi fish in general. Koi are only utilised as ornamental fish in koi ponds. Koi ponds often contain many fish that are regarded for their attractiveness. Even though koi are more expensive than most carp kinds, their value is based exclusively on their elegance and sleek appearance when swimming in fish ponds.