It is better to enrich the Artemia nauplii after 2 days of hatching. The enrichment time may be varied based on the object which you need to enrich. 4 to 6 hr enriched Artemia will be given better results.
You should use Artemia of at least the Instar II stage for enrichment. Nauplii start to hatch from the cysts typically after 18-22h of incubation. The nauplii that hatch are from the Instar I stage (without open mouth), so enrichment at that time does not make sense. About 8h later, the nauplii molt into the instar II stage and their mouth opens. This is the time that you can start to enrich. So summarizing, enrichment can start at about 26-28h after incubation of the cysts (nauplii that are still at the instar I stage at that time will molt into instar II during enrichment, so these will also be enriched)
The time of enrichment depends on the product you want to enrich with. For commercial applications it is often enriched with an emulsion high in DHA that is typically applied for 24h (this allows the tissue to incorporate the DHA as well). In case of for example scientific purposes, it is often the goal to just stuff the gut with a specific (particle shape) compound. Then the gut can already be full after 0,5-1h of enrichment. We normally apply at least 2-3h to be sure.
Since instar I nauplii completely thrive on their energy reserves they should be harvested and fed to the fish or crustacean larvae in their most energetic form, (i.e. as soon as possible after hatching). For a long time farmers have overlooked the fact that an Artemia nauplius in its first stage of development can not take up food and thus consumes its own energy reserves. At the high temperatures applied for cyst incubation, the freshly-hatched Artemia nauplii develop into the second larval stage within a matter of hours. It is important to feed first-instar nauplii to the predator rather than starved second-instar meta-nauplii which have already consumed 25 to 30% of their energy reserves within 24 h after hatching . Moreover, instar II Artemia are less visible as they are transparent, are larger and swim faster than first instar larvae, and as a result consequently are less accessible as a prey. Furthermore they contain lower amounts of free amino acids, and their lower individual organic dry weight and energy content will reduce the energy uptake by the predator per hunting effort. All this may be reflected in a reduced growth of the larvae, and an increased Artemia cyst bill as about 20 to 30% more cysts will be needed to be hatched to feed the same weight of starved meta-nauplii to the predator (Léger et al., 1986). On the other hand, instar II stages may be more susceptible to digestive enzyme breakdown in the gut of the predator since these enzymes can also penetrate the digestive tract of the Artemia through the opened mouth or anus.
Although the larvae lose its nutritional value very fast, it´s a better idea to use instar II in stead of instar I, since the goal is to offer enriched Artemia. The key is in the enrichment product. The best time would be just before begins moulting
It is up to you, if you want to use nauplii it is the best, enriched 24 h after hatching first for first 12 h and then for 12 h again, totally 24 h.
Dear Dr Hadi Jamali . See the following useful link: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5413311/
Kindly see also the following useful link: http://jifro.ir/article-1-267-en.pdf
Also check please the following good link: https://www.google.com/amp/s/scialert.net/fulltext/amp.php%3Fdoi%3Dpjbs.2006.2159.2161
The following link is also very useful: https://www.scirp.org/html/10-2270459_52776.htm
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