The word "rotifer" literally means "wheeled animals". Rotifers are not naturally found in saltwater, but instead in fresh and brackish waters. What makes them so valuable to us is the fact that a single rotifer has the potential to become several thousands in a very short time of a few days. Additionally, rotifers are extremely small and able to carry valuable nutrients to our young fry and filter-feeding invertebrates. Rotifers are not very nutritious by themselves so it is important to understand the importance of providing them with a nutritional diet.
The two commonly availed saltwater variety are of the L-strain and the S-strain, the S-strain being the smallest at about 150-220 microns in length.
Cilia - These small hairs circulate water and nutrients towards the mouth
Stomach - This area as well as the intestines is were the most nutrition is held for later consumption by our fry and filter-feeding organisms.
Foot - utilized to temporarily attach themselves to the substratum
Corona - lip that are lined with the Cilia
Mastax - a muscular pharynx containing a complex set of hard jaws
Pseudocoel - surrounds the eternal organs and the digestive tract
Female rotifers produce eggs which hatch with in 12-hours. In poor conditions, rotifers begin to develop halpo-identical offspring which are much smaller. They are non-feeding rotifers which fertilize other halpo-identical eggs. These fertilized eggs form a hard shell and are called "cysts". Cysts can survive poor conditions as well as remain dormant for periods of a couple of years. When conditions are favorable once more, these cysts hatch and reestablish themselves. It is these cysts that are used (when a living culture is no available) to start our cultures
Cysts are placed in saltwater that has a specific gravity of 1.014, a pH of7.9 or close to, and a temperature of 70 - 85 F.
An air stone is used to provide a slight aeration. Mild light from one standard fluorescents bulb will suffice. Cysts will hatch within 18-24 hours.
Rotifers are continuous and heavy feeders which require an almost constant food supply. Greenwater is the idea food of choice for rotifers and the drip method is a good method for providing this reqired diet.
Nannochloropis is among the best algae for rearing rotifers (see green-water).
Information on starting and maintaining a greenwater culture can be found at:
http://www.garf.org/news13p2.html#green. This is a very well written, in-depth article that should shed some light on greenwater cultures.
There are also pre-prepared cultures that are available and ready for use. Additionally, another possible food-source (though far less nutritious than greenwater) is fortified yeast. Rob Toonen's article also discusses that as well.