What makes koi grow fast and fat?

Koi grow fast and fat on protein- and fat-rich foods like brine shrimp, cicada pupae, mealworms, and red worms – but don’t dump too much at once, or they get indigestion and leftover food spoils the water and ages it faster.

For balanced nutrition, also feed koi pellets plus fruit, vegetables, water plants, rice, bread, and steamed millet, and add vitamins regularly.