Place heads & bones in large pot, cover with water. Add 2 carrots cut into rounds, 2 large onions, 2 stalks celery. Salt & pepper to taste. Cook broth while preparing fish.
Have fish store grind the fish or you can grind it yourself. You can chop or the easy way is to use a mixer and mix all ingredients for about 15 min until gooey. As you are chopping or using mixer add about 1/2 cup water & 1/4 cup matzo meal. With dampened hands form oval ball & add to boiling water. I usually get 4 pieces per pound. Cook for 3 hours after putting in first fish ball (low rolling boil). Cover pot & shake pot every so often so that fish doesn't stick together.