Koi (Cyprinus rubrofuscus) is a domesticated colored variant group of Amur Carps originally found in Asia and Central Europe. The colorful scale pattern has made Koi fishes one of the most popular aquarium fishes worldwide. A case of a female Shusui Koi aging 7 years old was brought to Dr. Fish clinic located in Tehran, Iran. The owner has reported 3 months of abdominal inflammation, no problems with feeding or balance and no sign of sickness. In the clinical examinations and microscopic investigation via wet mount, skin and both gills were found healthy. Lateral and dorsoventral radiographs were taken. Both graphs showed a displacement of swim bladders due to the presence of tumor-like mass surrounding them. Sonography was done in order to further identify the mass. Swim bladder was found to be completely out of place due to the accumulation of eggs (egg binding) in the abdominal cavity. The egg bound Koi had been unable to release the eggs for months. The owner was advised to give the fish a short time to release the eggs naturally. When the natural course did not take place, the fish was brought back to the clinic for the first step of hormonal therapy. An intraperitoneal injection of GnRH (Ovaprim™) was done under the pectoral fin. The first injection dose contained 10% of the therapeutic amount. The next and final injection containing the remaining amount of the hormone, was done 24 hours later. The Koi was able to release the eggs shortly after the treatment.
