"Infusoria" was the old-fashioned aquarist's quaint expression for a dense culture of protozoans, especially rotifers and ciliates such as Paramecium but including flagellates and amoebas. An infusion is a watery solution produced by steeping or macerating vegetable matter; the summertime "sun tea" you brew out on the deck is an infusion. "Infusoria" populations bloom in infusions of manure or decaying vegetation. The most nutritionally desirable of the planktonic protists are probably rotifers, but the ciliates also provide good nutrition. The most familiar among the ciliates is Paramecium, the "slipper animalcule" you might remember from High School Biology. Paramecia multiply mostly by fission, with a little sex on the side from time to time. This flexible strategy helps them multiply very fast, so your culture will be mature in a matter of days. Paramecia and other non-photosynthesizing single-celled planktonic creatures feed on bacteria that are breaking down organic substances. So to culture them, you need to supply some decaying organic material, and to be patient for about four days' time at temperatures in the low 80s.

The "infusoria" culture you're after is no more than a productive concentration of the same "cloudy water" problem you avoid in the show aquarium. When similar plankton appears unbidden as a white bloom, especially in a new tank, we treat the phenomenon as a problem instead of a food culture. Ciliates and other microscopic plankton are always present in a mature aquarium, but in comparatively sparse numbers. They form an important link in the food web.

Culturing. Requirements for a ciliate culture, or "infusoria," are simple: a starter culture plus organic nutrients, exposed to strong daylight (but not sunlight) and warmth (83^oF is the ideal), at a stable and somewhat alkaline pH above pH 7.0. The culture should be cloudy but not milky-opaque, with a ripe "pond" odor but not a foul bacterial stink. Nevertheless, your family will really want you to keep a paramecia culture covered with a sheet of glass. Culture water that is too rich in organics, combined with not enough aeration, will simply encourage bacterial fermentation, which isn't what you want.

The starter can be filter-sponge squeezings in water from a well-established planted aquarium that hasn't been medicated recently. Or water from a fishfree plant nursery. Even water from a flower vase, as long as there were no additives in the water, would be more productive than raw, de-chlorinated tapwater. As I've mentioned, my own soft water needs a shallow layer of crushed coral to keep the pH above 7.0.

Organic nutrients spark the bacterial decomposition that forms the base of this rough-and-ready ecosystem. So you'll need to add some vegetal matter. Hay softened by boiling was traditional. Rotting leaf mold, oil-free lawn clippings, rabbit droppings, powdered cereal or instant mashed potatoes, baby food or hardboiled egg yolk crumbs, or stale fish food--— they all work. Wilted lettuce leaves left in the dry air till they're brittle, then crumbled, would be my first choice. Banana skins and sliced potatoes tend to encourage a lot of fungus, in my experience. If I were already running a DIY CO₂ setup, I might add just enough filtered yeast culture to faintly cloud the water.

Snails in the culture are good. (Aren't some Ampullaria even called "Infusoria Snails?") Their droppings encourage the protists, and the snails act like canaries in a mine shaft: when my Melania snails crawl above water level, it's high time to re-culture!

You may think you can skip this first stage by feeding the fry with a commercially-bottled liquid fry nutriment. These liquid fry feeds get very mixed reviews from experienced fishkeepers; one group states that whatever good such products are doing is possibly in providing a source of decay bacteria, which in turn feed the culture of protozoans that you're really after. In fact, a few drops of skim milk or liquid fry food are often recommended in culturing paramecia.

There are rigorous laboratory directions for culturing paramecia under sterile lab conditions in "The Zebrafish Book: a guide for the laboratory use of zebrafish Danio" part of information for biologists deciphering the zebrafish genome at the Zebrafish Information Network. Don't be too proud to look through "Zebrafish for K-12" also. In the lab culturing directions, you use distilled water, a brewer's yeast tablet, boiled wheatseeds (the "wheatberries" of your local healthfood store) and a seeding from a good clean young paramecium culture, all stored in strong light (not sunlight) and ready in 4 days at 28.5^oC. That would be 83^oF. You may not go about culturing so meticulously, but isn't it good to know the ideal temperature of a paramecium culture?

Charlie Grimes' simplest possible recipe for culturing a mix of Euglena and paramecium (the commonest kind of free-swimming ciliate) in Aquarium Fish, April 1997, required no more than a gallon jar of clean aquarium water and a dried pea! It has never been quite that simple for me.

Mike Edwardes suggests putting a slice of boiled potato in some rich old tank water, incubated in a brightly-lit window till it's cloudy with bacteria. He suggests continuous light aeration, as low oxygen levels inhibit aerobic bacteria. As the water clears, the protozoans are at their most numerous--— in 3 or 4 days.

Francisco Borrero had this "boiled greens" technique from his mother, a commercial breeder of danios and other egglayers:

"This is the best way I've found of producing good infusoria cultures for feeding small fry: I take several spinach leaves, any variety, and rinse them very well. Spinach, collard greens and probably others work just as well. Best but not strictly necessary is to use organic, or certified as with no pesticide. If it is not fresh it does not matter and may be even better. Put in a pot (I prefer a glass pot) and bring to just past boil. Turn off inmediately after boiling temp, or even just before. - Let this green water cool to room temp. I do this by placing it outside on the porch, uncovered. This may help innoculation. —Use as a food for infusoria cultures. If you let it sit in a wide mouth jar for a couple of days, it will "develop" infusoria. (quotations intended to avoid suggesting spontaneous generation, which of course does not happen). What I really do is to innoculate a fresh batch of cooled green water with a small amount of infusoria innoculum taken by pipet from a rich infusoria culture produced in the standard manner. Wait 1-3 days depending on temperature. - The result is much cleaner, denser and longer-living infusoria cultures than with standard methods. This method results in the virtual absence of the nasty bacterial decay film which is bad for fish fry, and bad for the infusoria culture. After producing the first culture by the lettuce green water method, I use this as an innoculum for suceeding batches. I start a new jar every 3rd day or so, allowing having constant supply of clean cultures. Start with clean jars. Soap residues in jars will result in slow or no culture happening."

Adrian Tappin"s "Feeding Rainbowfishes" section at "Home of the Rainbowfish" has some further culturing techniques.

Aquaculture Supply (with a link to their "aquasales.com") will sell you greenwater and plankton culture kits, with their famous and universally-recommended Plankton Culture Manual.

Feeding. The trick with feeding from a culture or innoculating a new one is getting a rich dropperful of paramecia without too many bacteria. Often there's a scummy lipid layer at the surface you'd also like to avoid. Ideally, you'd like to keep a steady supply of ciliates and rotifers available to your larval fishes, without actually culturing "infusoria" right in the fry tank. Try this: as the culture matures, the bacteria will use up most of the oxygen as they work on decomposing the organic substances. First, turn off any aeration you may be using. The resulting lowered oxygen levels through most of the culture will encourage the protists to gather after some hours in a shimmering milky layer in the only place where the stagnating culture medium contains some oxygen diffusing in from the atmosphere--— just under the surface. From there, you can draw them up in a syringe or a large eye dropper.

Alternatively, you can extract some paramecium culture in your "aquarium only" turkey baster and fill a tall narrow bud vase. After ten hours or so, you'll have a clean concentrated layer of ciliates at the top of the vase. With an eye dropper, you can remove them, either for feeding fry...

...or for seeding a more selective second culture of infusoria. The first culture you develop, using rich old unmedicated aquarium water, may prove to be less than select. But draw out some culture from the paramecium layer and re-culture that. Since paramecia multiply so quickly, they will outpace other plankton in the re-cultured medium. You'd better keep a couple of infusoria cultures going while you need them, because nothing crashes more unexpectedly than populations of protists.