A SIMPLE AND RELIABLE PROTOCOL FOR RAISING FRESHWATER ROTIFIERS AS BABY FOOD
By M.R. Naegeli and J. Wittbrodt, Biocenter of the University of Basel, Klingelbergstrasse 70, CH-4056 Basel, Switzerland
For a high survival rate and rapid growth of young fish, a rich baby food is an unconditional prerequisite. Artificial diets are messier than live food and tend to easily decompose. This requires time-consuming cleaning of baby cages. As a live food, paramecia are widely used, but contamination is a recurrent problem with paramecia cultures and the preparation of paramecia medium and the harvesting of paramecia is rather time consuming.
Here we present a simple and reliable protocol for raising freshwater rotifiers (Brachionus rubens) as diet for fish babies. The protocol can easily be scaled up and should reliably lead to the mass production of baby food. The care of a constant culture of rotifiers takes only a few minutes per day. In contrast to saltwater rotifiers, Brachionus rubens stays alive in the baby tank, does not sink to the ground and will help to keep the tank clean until eaten up.
We are currently in the 15th passage of Brachionus rubens we raised initially from a single batch of cysts. In our hands the rotifiers seem to reproduce happily.
deg. Start inoculating a culture of freshwater floating- algae (as you might find in one of your fish tanks) in a 1.5l sedimentation funnel of aged fish tank water. We regularly use 3-4 week old tank water.
deg. Grow algae in front (ca. 25 cm distance to the lamp) of a Phillips TLD 58 Watt lamp, slow air-bubbling, to an O.D.445 of 0.10.
deg. Now inoculate the culture with a few Brachionus dormant cysts and aerate very gently with a maximum of 1 bubble per second. The surface of the water should be covered with cysts. One spatula tip of cysts should be sufficient. Cysts are available as baby fish food in pet shops or at Ward's Biology Supply Catalog, #87 W 3120, $9 per 1000 cysts!
deg. This culture will now grow for ca. 3 to 5 days depending on number of cysts inoculated. Have a constant gentle air- bubbling and 12 hours of light per day at 28- 30C.
deg. A fully grown Brachionus culture contains up to 5000- 10,000 rotifiers per ml. Most of the algae (>99%) will be eaten up at that point. Be careful not to overgrow your culture, the rotifiers will die very quickly!!!
Inoculate new algae- culture (O.D.445 of 0.10) with 50- 100 ml of fully grown Brachionus culture.
To collect the rotifiers either sediment or filter through a fine meshed net (or a Falcon cell strainer #2350) or just take them as they are.
A few things to think of:
If the concentration of algae gets too high (Brachionus will suffocate over night in the dark period), turn off the light or reduce with a dark cover.
Don't forget to have 3 funnels of algae culture, so that you always have one ready to inoculate.
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