So your clownfish have bred and the eggs are looking about ready to hatch. Marine expert Matt Pedersen has some advice on feeding the babies, and on enriching baby brine shrimp for marine fish fry.
In truth, the gut loading of baby brine shrimp (aka. Artemia nauplii) may not be necessary for baby clowns, but it certainly won't hurt. The reality is that some baby clownfish can be weaned straight from enriched rotifers to rotifer-sized larval feeds such as Otohime A. I've personally introduced such larval feeds as early as 4-5 days post hatch, while maintaining rotifers until the larvae are fully weaned, and in fact I've managed to rear clownfish without using brine shrimp nauplii at any stage.
I am aware that at least one commercial clownfish hatchery in the USA does not hatch baby brine shrimp for any of their clownfish. However, just because you "can" doesn't necessarily mean you "should" or that it's the best way to do it! And for other marine fish babies, you may certainly need baby brine to elicit a feeding response.
I should address why you may need to gut-load, or enrich, baby brine shrimp. The simple answer is that brine shrimp not a true "marine" species. The result is that they do not naturally have the high levels of DHA that marine species, such as Copepods, contain. Larval marine fish of all types require DHA, as well as EPA, for proper development.
When these HUFAs (Highly Unsaturated Fatty Acids) are deficient from the larval diet, the result is that babies are susceptible to shock-related deaths. This is typically referred to as SFS (Sudden Fright Syndrome), where any sudden stimuli can result in the baby fish appearing stunned, sinking to the bottom, twitching, and possibly ending with their death.
The method of bringing clownfish directly from rotifers to prepared larval diets works to prevent SFS because the prepared foods contain the required HUFAs. There is no reason you cannot offer both larval diets and baby brine shrimp together to your baby clowns.
You cannot "enrich" newly hatched brine shrimp. The first stage after hatching is known as "Instar I", and at this stage, the nauplii has no mouth. In other words, it can't eat, so it can't be gut loaded. You can "soak" this stage in a HUFA solution like Super Selcon, but at best, you're hoping that some of the enrichment solution adheres to the outside of the baby brine shrimp and is consumed by the baby fish.
You may need to start offering Instar I nauplii due to their small size – waiting to enrich the baby brine shrimp might result in a nauplii that is too large to feed on, and calorie wise, "Instar I" is superior to "Instar II". Soaking will be your only real option until the baby fish are large enough to accept the next stage.
Because Instar I does not feed, you have to wait for the baby brine shrimp to grow and molt, entering Instar II. Indeed, it will be about 12 hours after hatching to reach this stage. At this point, the baby brine shrimp can take up enrichments like Super Selcon or phytoplankton (you can use live phytoplankton or any number of prepared phytoplankton products).
The actual length of time needed to enrich varies depending on which author you reference. Given that brine shrimp do not always hatch in unison, the best approach would be to add enrichments six hours after hatching, and harvesting the nauplii for use somewhere around 14-16 hours after hatching. You may also wish to refer to the manufacturer's own instructions for enriching with their particular product.
The bottom line is that for baby marine fish, brine shrimp nauplii are a somewhat inferior food. The use of copepod nauplii when possible would be much more beneficial (and in some cases it is known to be required), although it is much more complicated and intensive to provide at this time. Thankfully clownfish are "forgiving", and baby brine shrimp need only represent a week or two of larval feeding at most.
For more information on working with the myriad of plankton utilised in marine fish culture, I strongly suggest tracking down a copy of the "Plankton Culture Manual" by Frank Hoff of Florida Aqua Farms. This book is currently in its 6th edition.
Check out Matt Pedersen's other marine fish breeding q and a's on this website: