Under normal circumstances, Koi fish will not actively eat other fish, but they may do so under certain specific conditions. Koi fish are omnivorous. They usually feed on algae, aquatic plants, plankton, insect larvae, and artificial fish feed. Their habits are relatively gentle, and they will not actively prey on small fish that are healthy and not significantly different in size from them. However, Koi fish may eat other fish in the following special situations:
Hunger State: When Koi fish are in an environment with extremely scarce food for a long time, in order to obtain sufficient nutrients to maintain their vital activities, they may prey on small fish.
Sick or Weak Small Fish: If a small fish is already sick or injured, and is weak in body and slow in movement, its special smell or abnormal swimming posture may trigger the predatory instinct of Koi fish.
Mixed Breeding of Juvenile Fish and Adult Fish: If very small juvenile fish are mixed and raised with large Koi fish, the Koi fish may mistake the juvenile fish for food and swallow them due to being unable to distinguish clearly.
In addition, in nature, Koi fish can also eat small fish and other meat-based foods, but they usually do not take them as their staple food. Instead, they occasionally eat them as an additional meal. Therefore, under normal breeding environments and with an adequate food supply, Koi fish and small fish can coexist relatively harmoniously.