Koi enjoy variety. Some human foods are perfect treats; others are dangerous.
Safe Treats
Watermelon, oranges, lettuce, peas (mashed, skin off), cooked rice. Cut to bite size.
Insect Treats
Mealworms, crickets, silkworm pupae. High protein, koi love them. Source from pet feed suppliers, not wild caught.
Avoid
Bread (causes constipation), corn (poorly digested), seasoned/salted human food, processed meat. Anything with garlic, onion, or chocolate.
Treats as % of Diet
Max 10% of daily calories. Nutritionally incomplete — pellet food remains the staple.