Feeding should be stopped when the water temperature falls below 10°C, primarily due to significant physiological changes in koi and the need to protect their health. At such low temperatures, koi metabolism slows dramatically, and digestive enzyme activity nearly ceases. Food ingested during this period cannot be properly digested and may stagnate in the intestines, fermenting and easily causing enteritis or dropsy. Additionally, koi immune function is suppressed in cold water, and undigested food can promote bacterial growth, greatly increasing the risk of infection.
Below 10°C, koi enter a semi-dormant state, relying on fat reserves accumulated during summer and autumn to meet their energy needs. Forced feeding under these conditions would place unnecessary stress on their liver and other organs. Although decomposition of leftover food slows in cold water, the gradual accumulation of toxins such as ammonia is more dangerous because nitrifying bacteria are also dormant and cannot effectively break down these harmful substances. This can lead to long-term poisoning of the fish.
Therefore, stopping feeding avoids digestive strain, conserves the koi's energy reserves, and prevents long-term water quality deterioration. Feeding should only be gradually resumed once water temperatures stably rise above 10°C, starting with small, easily digestible portions to allow the koi's digestive system to reawaken safely.
