Karasu are solid black koi that have a white, red, orange or yellow belly. Karasu are typically fully scaled koi. Any doitsu (scaleless) solid black koi is most likely a Kumonryu whose pattern has changed to solid black.
What To Look For
Since Karasu have no pattern, body conformation is of the utmost importance. The head should be symmetrical and proportionate to the rest of the body. The nose should also be proportional to the rest of the koi, and should not be too short and stumpy, nor too long and extended. The body should also be symmetrical, and should display a torpedo-like shape, meaning that it is thick behind the head and tapers down evenly toward the back of the body. The fins should also be symmetrical and free of deformities.
Beware of any scales that are missing or blemished, as these will be readily apparent on a black koi with no pattern. Also, the head should be smooth and even colored, with no blemishes or flaws. The fins should be solid black all the way to the tips. If there is any white showing on the tips of the fins, the koi is classified as a Hajiro.