Koi fish do eat tadpoles, especially small or slow-moving ones. Below is a detailed analysis of this behavior:
1. Reasons Related to Diet
Omnivorous Nature: Koi are omnivorous, with a diet that includes aquatic plants, algae, insects, and small crustaceans. Small live creatures like tadpoles are also considered food sources.
Predatory Behavior: Koi have a pecking habit. When they encounter slow-swimming tadpoles, they may actively attack and swallow them.
2. Influencing Factors
Tadpole Size: If tadpoles are close to the size of a koi’s mouth (e.g., over 5 cm in length), the probability of being eaten decreases.
Hunger Level: Koi are more likely to prey on tadpoles when food is scarce.
Environmental Space: In narrow water areas, tadpoles have fewer chances to escape, increasing their risk of being eaten.
3. Exceptions
Large Tadpoles: For example, bullfrog tadpoles (which can grow over 10 cm long) are usually too big for koi to swallow.
Adequate Food Supply: If koi are well-fed and there is a large number of tadpoles, koi may reduce their predatory behavior toward tadpoles.
4. Recommendations
Avoid Co-Habitation: If you want to protect tadpoles, keep them in a separate tank or co-house them with gentle fish species (such as goldfish).
Provide Hiding Spots: Adding aquatic plants or placing rocks in the tank can help tadpoles hide from koi.
Summary
Koi fish actively prey on small tadpoles. Whether to keep them together should be determined based on your specific situation (e.g., tadpole size, food availability, and tank space).