Culturing Method
There are many ways to raise rotifers, the following is how I do it.
Step 2) Place the starter culture in a 5 gallon bucket. Add enough fresh saltwater with a specific gravity of 1.015 to double the water volume in the bucket. Feed with IA using the recipe below.
Step 3) Insert a rigid airline tube connected to an air pump to provide aeration.
Step 4) On day 2, add enough saltwater to double the volume again. Increase the water volume again on the next day.
I find that maintaining about 4 gallons of water volume in a 5 gallon bucket works well.
Rotifer feeding protocols when using IA Rotifer Diet:
Dilute concentrated IA by adding 50ml to a 2L bottle and filling with fresh SW at 1.015SG.
Feed 10ml per gallon of culture size, twice a day. ie; if you have a 4 gallon culture, add 40ml of the diluted concentrate twice a day.
EDIT: Due to technological advancements since I started this thread I'd like to make some updates. Reed Mariculture has released a new product called RotiGrow Plus. http://rotifersolutions.com/?page_id=231 In a few words, this is an improved formulation of the IA Rotifer Diet specifically targeted at raising rotifers. I dilute RG+ in the same way as the IA RD and use the same feeding protocols. I've found the RG+ to be superior to the previous product.
You NEVER want to allow the rotifer culture to become completely clear. It is absolutely necessary to keep the rotifers fed constantly to obtain a dense culture. Without a dense culture, you may wake up one day and find that there is no more food left for your fry. Feeding smaller amounts, more frequently, is optimal.
Rotifers should be harvested every few days by using the 120 and 53 micron sieves. The 120 micron sieve will strain out the larger particles and the 53 micron sieve will collect the rotifers:
After a few days you will notice a build up of detritus on the bottom of the bucket. This should be removed either by direct siphoning or stirring the culture before straining it.
Harvesting: Using a water pitcher I remove culture water and pour it through the sieves and back into the culture vessel.
Refreshing: Following the procedure above, 50% of the water is drained into a waste bucket instead of into the culture vessel and replaced with fresh salt water.
This information is a summary of what I've learned from my own experience as well as knowledge obtained from reading "Plankton Culture Manual - Frank Hoff" and "Breeder's Guide - M. Wittenrich".
Enrichment
After rotifers are harvested they need to be enriched before using them as food for the larval fish. Highly unsaturated fatty acids (HUFA's) are of prime importance to the survival of marine fish larvae. Since rotifers themselves offer little nutritional value on their own they need to be enriched with HUFA's. The fatty acids, EPA and DHA, are the most important, with DHA the most essential.
Nannochloropsis and T-ISO phytoplanktons are commonly used. Nannochloropsis contains high levels of EPA and T-ISO contains high levels of DHA so a mix of both is commonly used for enrichment. The ALGAMAC enrichment products are also a great alternative to IA.
After harvesting, back-flush the 53 micron sieve with clean water using a turkey baster. I usually do this into a small plastic food container. After you have all the rotifers in the container add the enrichment and allow them to feed for 8-12 hours, depending on the instructions from the manufacturer. The specific type of enrichment you use will depend on the needs of the type of larvae you're working with.
Once the rotifers are enriched they should be rinsed with clean tank water before being added to the larval tank.