I seem to remember that brine shrimp take at least a day before they can eat and live off a yolk sac.
After hatching, at about the 24 hour mark, they have developed two appendages (swimming legs), antennae and an eye spot and are ready to be harvested.
They are now called Instar I nauplii. They have no mouth or anus as they are still developing. At this stage they have a egg yolk reserve to aid them through the next stage of development. This makes them highly nutritious for some fish fry. They can not be enriched or gut loaded at this stage because they are not developed enough to eat. They also have no mouth or anus.
Day 2 (approx 12 hours later) they begin to molt into the second larval stage called Instar II nauplii, they have a mouth and anus and a immature digestive tract.
When newly hatched, Instar I nauplii are high in fat content, they still maintain a yolk sac, and for many fish fry species this is ideal. The fat content begins to decrease as they grow and by adult stage they are higher in protein than fat. If not fed 24 hours after hatching, their nutritional value begins to reduce. Ideally fish fry need higher fat content in the early stages of life and as they get older their need for protein increases.
The nutritional profile of brine shrimp can be enhanced by “enrichment” or “Gut Loading” . Newly hatched artemia (Instar II) take approximately 18-24 hours to be fully enriched, while adults need only 6-8 hours. Medium sized vary between 10-14 hours.
This is a few quotes from one article I found.
I want to try to get them to eat, the man who gave them to me said he was having no luck
