John, NLS contained soybean isolate, which is worlds apart in quality, and cost, compared to the terrestrial based grains used in SD. Soy isolate is very high in protein (80+%) wihch means a much smaller inclusion rate could be used, and unlike most terrestrial based grains soy isolate contains no anti-nutritional matter. That's why it costs so much $$$$, and why you seldom see a fish food manufacturer using it in their food, and instead, using soybean meal, or whole soybeans, such as in SD. Pablo dropped isolate from NLS a couple of years ago after he began making his own foods on site at his own facility. To replace it he bumped up the herring & krill inclusion rates - which while costing more $$$, became doable once he removed the middle man (the feed mill) from the equation. SD can't do things like that because they are paying Zeigler for being their purchasing agent, and to make their food.
Again, I'm not arguing the fact that one can grow out a fish in a reasonable manner on any tropical fish food. Even the lowest quality crap based mostly on fiber will get the job done in a pinch. As an example, check out this pond set up, John. You'll appreciate this as I see that you just recently got into these fish.
http://madagascares.com/Ebooks/FishFarmUpdateJuly2013.pdf
For those that aren't familar with this species, these are Paratilapia pollini "Andapa", raised by the locals for food, and for introducing back into the local waters as most fish in this area are endangered, some even now extinct in the wild. The adult fish in that pic is approx 9", and their diet in that pond is 80% rice hulls, and 20% dried shrimp. Rice hulls have the nutritional equivalent of straw. 2-3% crude protein, .5% crude fat, 40% crude fiber, 30% carbohydrates, 15+% ash - you get the picture. They might as well been feeding these fish dried rabbit turds, yet they still grew and are in relatively good health. Perhaps they gleaned some nutrients from the pond via insects, larvae, etc, but the bulk of their diet was from the rice mash mix.
And while SD may have now removed feathers from their food, how does one trust a vendor who was just days ago defending the quality of those feathers? I'm quite certain that the fish farmers in Madagascar know, and would admit, that they are feeding low quality feed as they barely have enough food to feed themselves most days, but what's the excuse from the folks at SD?
