Here's an except from an article written by a researcher:
There is a myth floating around that adult artemia are not as good for your fish as newly hatched. There is a tiny bit of truth to this, but it depends on what you are feeding. So whats in it for your fish: Newly hatched artemia are high in fats, about 23% of dry weight. By mid juvenile stage, the fat levels have decreased to about 16 %, and by the time they are pre-adults the fat levels have decreased to about 7%. But, at the same time, the protein content has risen to replace the fat, from about 45% in a newly hatched artemia to about 63% in an adult. Based on this, you should determine what is best for your tank, young fish larvae require a high fat intake for growth and health, while older juveniles and adults need protein for health and reproduction. Also, nauplii are known to be deficient in several essential amino acids, while the adult artemia are rich in all essential amino acids. Adult artemia therefore supply more biomass than nauplii and are more nutritionally complete.
-----------------------------------------------------------------------------
There are other good article about adult brine shrimp. I am at work right now and I cannot get to the article about the nutritional content of adult brine shrimp vs. bbs. It might have had a comparison chart on mysis as well. My break time is almost over so I have to dig it up later. I don't recall that there was a lot of difference between the two, though.
As long as you have a good clean up crew, I find frozen food from reputable suppliers are good enough for breeding fish. I would not really see extra merit in growing your own live food except it can be a lot of fun to do so for some of us.
Tomoko
Tomoko