The late Dr Myron Gordon, who was Fish Geneticist with the New York Zoological Society for many years and an active aquarist himself, used the following formula for feeding his tropical fish. It is also suitable for feeding to smaller goldfish. The quantities given may be modified to suit special needs.
Remove the blood vessels, connective tissue and other fibrous material from one pound of liver, and cut into 1/2-inch cubes. A scissor is handy for this.
Taking small quantities of liver at a time, add equal amounts of cold water and blend them in a high-speed blender. The resulting liquid should be strained into a large bowl. Add two teaspoons of non-iodized salt.
To this add 20 tablespoons of a precooked baby cereal such as Pablum , and stir thoroughly
Fill small glass containers, such as baby food jars, but do not cover them. Place them in a pan of water and bring the water to a boil. Allow the jars to remain in the water for half an hour after the heat has been turned off and when they have cooled, cover them and keep refrigerated or frozen.
Small portions (the size depending on the number and size of the fishes) may be fed as often as desired. The advantage of this formula is that the blood will not leach out into the water, and a lump placed on the bottom of the aquarium will be picked at by the fish all day long. The uneaten portion may be removed in the evening.

(Goldfish Guide by Dr. Yoshiichi Matsui TFH Publications Inc.)