You can do very well at a fish (food, not pet type) by buying your scallops and shrimp, etc., and then asking for the heads and tails. Many people ask the fish monger to remove the heads and tails from the fish they buy, and they are usually are thrown out. However, if you are a customer (after all, you bought the scallops, shrimp, etc.) they will usually give these parts to you for free. There is lots of meat in these parts, and you can use it to complete your recipe. I don't like the recipe given above because it will tend to disintegrate in the tank, and too much waste is left behind (unless you have some pretty good filter feeders). I mix my homemade fish food with Knox gelatin, which acts as a nutritious binder (it is protein) that holds the food together.
Jay