During the summer months, many koi need diets that are higher in protein, due to their seasonally changing body functions. This means that simple earthworms can provide a tasty and important treat to koi fish. Some koi breeders also use clams or prawns as feeder to serve this purpose.
Feed koi whole grain brown breads torn in pieces. Avoid using white bread. Koi also enjoy cubed and cooked skinless sweet potato, as well as peas, corn, watermelon and pieces of orange.
Chop up 1/4 cup spirilina, four sea weed wraps (Nori brand in the sushi aisle), 1/4 cup dried krill (optional), 2 tbsp. brewers yeast, and 1 tsp. garlic.
In a separate container, chop 1 cup fish (tilapia, cod, etc.), 1/2 cup shrimp, and mix in an egg. Add this to dry ingredients, then chop 1/4 cup broccoli and 1/4 cup carrots (optional) and add to your mixture. Lastly, add 1 cup wheat germ and 1/2 cup flour. Mix until dough forms, then place on baking sheet in plat patties and bake at 375 degrees F for 10 to 13 minutes.
Despite our tendencies to feed koi at the surface, they also enjoy feeding pastes which will drop below the surface for them to feed on. One recipe includes 12 canned sardines, 2 lbs shrimp, 2 cups cooked rice, 6 cloves of garlic, and a cup of orange juice pulse chopped in a blender and mixed with gelatin.