Excellent point DD1.

One of the very key things we can't judge or check except through longer term use is content quality. I have had long discussions with PhD animal nutritionists (fish specialists)and they stress the importance of quality control. Especially with protein sources and production methods. Not just the type (fish meal from oily fish like menhaden is best) but also how they are processed. There are huge differences in the value of the same % protein based not only on source but also on how it is processed. It does not matter if you use 50% protein and 20% lipids if the fish can't digest it and absorb it into their system it goes for naught. The best approach is to match the food content amino acid complex to that of the species being fed.