Same thing with cat food. I don't know about fish, but with both dry cat and dog food, ingredients are listed in order by volume, greatest to least measured by weight, and the first three ingredients make up the bulk of the food, and at lease one of these three should be a good meat source.. This makes it a bit easier when reading ingredient labels. Also, the Department of Agriculture has layed down strict rules for the termanology. If it says simply "chicken" this means chicken meat, the same cuts a human would eat. "Byproducts" means the less desirable parts like intestines, stomachs, skin, whatever. While animals in the wild would eat these parts of their kills, and it does help balance their nutrition, meat is better. Also, the term "meal" means animal products that have been ground up and dehydrated. Since ingredients are ranked by weight, having the water weight removed means you are getting more of the animal product for the wieight. On the other hand, this processing to cook, grind, and dehydrate the animal parts does remove some of the nutrient value. Still, "chicken meal" is better than "chicken byproduct meal".
I hope this makes label reading a little easier. I got most my info from a vet-tech friend and several pet food reps, so I trust it to be fairly acurate. (I hope).