Here's a good read on fish food labels:
"This subject seems to cause a great amount of confusion, so much so that I felt the need to address it in this article. For the most part the fish food industry is self regulated, basically meaning that it is very easy to manipulate an ingredient list to favor your own product. As an example, if the ash content is quite high in the food, the easiest way for a manufacturer to address that issue is to simply not list the ash content on their label.
Ash can come from bones, shells, and scales of marine animals that are high in calcium and phosphorous; to an extent its presence is simply unavoidable. But, the ash from minerals that come from raw ingredients such as Kelp and Spirulina, though beneficial, should be limited. If an excessive amount is used it can have a negative effect, since fish can assimilate only so much mineral content, and any excess will simply be adding unwanted pollution to the aquarium water.
A manufacturer can also use very little of a common raw ingredient such asspirulina, but use green dye to color the food, and promote it as spirulina food designed for herbivores. If you read the label closely, in some cases you may find that the food that was designed for herbivores may in fact be based on generic fish meal and contain very little spirulina or vegetable matter, but instead is loaded with fillers such as corn, bran, middling, flour, potato, etc.
A manufacturer can list Lobster and Crab in their ingredients to signify quality, but in reality it is nothing but the leftover parts of the animals.
A manufacturer can also choose to list many species of fish, one species after another, which gives the illusion that the binding agents (such as middling and flour) are several ingredients down on the ingredient list. The fact is that no matter how many types of fish make up the main ingredient, they are still just part of a single fish meal, period. As an example, if one used 500 lbs. of fish meal per ton of food, it doesn't matter how many species of fishes you use to get that 500 lbs., in the end it's still 500 lbs. of fish meal, and the true second or third ingredient will usually be a binding agent such as flour. Many unaware hobbyists see several kinds of fishes listed at the top of the ingredient list, followed by wheat flour, and assume that this particular brand must have very little wheat flour, and a very high concentration of fish protein. In reality it is no more than a single generic fish meal being used, comprised from numerous species of fish. All fish foods require a high quality binding agent, or they would simply fall apart long before they reached the aquarium. Premium foods use as little as 25% binding agent, while lower quality foods can be as high as 50% of middling and flour.
There can also be an extreme range in the utilization of nutrients and overall digestibility within any ingredient category. Shrimp meal is typically comprised of heads and shells, and many fish meals are typically made up from the processing waste of the fish, not the whole fish. Needless to say, a high quality food uses only whole fish, Krill, Mussel, etc., not leftover waste from processing plants."
http://nlsfishfood.com/index.php?option=com_content&task=view&id=29&Itemid=63&limit=1&limitstart=1
@ACWO
