A koi cannot become pregnant. They lay eggs. A female koi is verv fat, especially when full of eggs. This is usually in the summer. They also tend to have shorter noses. The males develop white spots called gill tubericules when they sense it is time to mate. However, one can know that the female is full of eggs by ligtly rubbing her sides towards her anus. DO NOT SQEEZE THE FISH!! Eggs will come out. Really the best sign is that the males are chasing her all over the place and smashing her into the sides of the pond. BE VERY CAREFUL! Many people have lost fish who leap from the pond in the dead of night. Check the pond regularly. Check it in the middle of the night! If you want to have any baby fish left, be sure to put in some grass mats or hiding places. Koi eat eggs and their own young. Go to the website koivet.com