As of my knowledge cutoff in September 2021, the record for the largest koi fish in the world is held by a koi named “Big Girl.” This enormous koi measured 4 feet, 3 inches (130 centimeters) in length, and weighed approximately 90 pounds (40 kilograms). Big Girl was bred by Kenichi Hagiwara of Hirasawa Koi Farm in Japan.
However, it’s important to note that koi fish continue to grow throughout their lives, and there may be larger koi fish that have been discovered since my knowledge cutoff. The size of koi fish can vary depending on genetics, nutrition, and environmental factors. Some koi fish can reach impressive sizes, but they are relatively rare compared to the average size of koi fish commonly seen in ponds and aquariums.
If you are interested in discovering the current record-holder for the largest koi fish, I recommend checking with official koi fish organizations, such as the Zen Nippon Airinkai (ZNA) or the All Japan Nishikigoi Promotion Association (AJNPA), as they may have the most up-to-date information on record-breaking koi fish.