You may have missed the part where I mentioned that some fish WILL NOT start eating ANY other food other than live. They will die first. Would you rather have a fish die than get it eating so you CAN convert it to other foods?
Even at that, some fish will never convert, and some fish like the hawiian cleaner wrasse, will never eat anything you can provide to the tank.
With all due respect for Fenner, I believe he also is just passing on information he believed to be true without the knowledge that live brine shrimp is a major industry to supply food for the mariculture industry, not as the main or only food but as a part of a regulated diet.
As for long term survival on brine shrimp, for the first 5 years of my salt hobby I fed my tanks frozen brine shrimp and to my tangs, algae sheets we now call nori.
I use the live brine now to augment my fish food diet by gut loading them with Selco, and spirulina. (this on about a weekly basis) Ocassionally when I get a fish that is hard to start eating I use the live brine for that.
The french angel was not suffering because the brine lacked nutrition, it suffered because like many fish, it's system has been evolved to handle plant form foods like the various algae. Likewise, there are fish that will suffer the same way if you try to feed them primarily on spirulina type foods and not meaty foods.
That angel will eat meat foods but it NEEDs algae for it's best health.
The best analogy I can think of at the moment would be with respect to farm animals.
A cow will rapidly deteriorate if you fed him only meat foods, if you could get it to eat them, and a pig would rapidly go downhill also if you only fed it grass etc....
That doesn't mean there is no nutrition in either of those foods but it does mean that not all foods will work for all eaters.
