Koi populations refer to the groups of koi, which are colorful varieties of carp commonly kept in outdoor ponds and water gardens. These fish are known for their vibrant colors and patterns, making them popular among enthusiasts. Koi can live for many years, with some reaching ages of over 200 years, depending on their environment and care. The size of koi populations can vary based on factors such as pond size, water quality, and available food. Proper management is essential to maintain a healthy koi population, including regular monitoring of water conditions and ensuring adequate space for each fish to thrive.