Remember that word? It's one of those aquarium world "catch-alls"; a sort of "hangover", if you will, from a gentler, kinder era in aquaristics. A time when under gravel filters, freeze-dried foods, and airmail of tropical fishes from Florida to you were considered state-of-the-art, cutting edge things.
"Infusoria" may be described as a real "catch-all" term for small aquatic organisms, like euglenids, protozoa, unicellular algae, tiny invertebrates, and that are commonly found in freshwater environments, like ponds, creeks, and drainage ditches, used as a first food for tropical fish fry. Sometimes, it's referred to as "green water" in older hobby literature- a kind of vague descriptor.
In modern formal biological classification, the term "infusoria" is considered an antiquated, obsolete descriptor, as most of the organisms previously included in the collective term "Infusoria" are assigned to a different assemblage of taxonomic groups.
Nonetheless, it's a charming, albeit somewhat antiquated term that is still used in aquarium circles to describe the tiny organisms that arise when you soak some blanched lettuce, vegetable skin, or other plant matter in a jar of water. They're perfectly sized for young tropical fish fry as the first food when they are free swimming. In fact, at around 25-300 microns, these organisms are consumable by most fishes as soon as they've absorbed their yolk sac.
Sounds good, but how do you "make" the stuff?
Well, traditionally, it was done in the most low tech way: You would take some blanched lettuce leaves, old flower clippings, hay, etc. etc. and basically let the stuff decompose in water, and after several days, a smelly solution of cloudy water will arise, driven by bacteria. Ultimately, after a few more days, the water will clear when creatures like Paramecium and Euglena arrive on the scene and consume the rampant bacteria population. Voila, in theory, you have an "infusoria culture."
Well, yeah, but the problem is, the density of desirable animals to plain old water is pretty low when you culture this way, and you'll most likely be "feeding" your hungry fry with drops of stagnant water, little more. The more modern approach would be to obtain a pure starter culture of Paramecium from an online biological supply house (yeah, their are plenty of 'em- just do a Google search). Here's my fave. Paramecium average around 150 microns in size- perfect for free-swimming tropical fish fry!
You can use the aforementioned decomposing lettuce as a start, or you can elect to be a bit more clean and modern and use brewer's yeast (which comes in tablets) that you'd use at a rate of like 1/2 of a tablet to a 1 liter bottle. Sure, there are probably more exact numbers to employ, but this is a hobby, right? I'm telling you what worked for me. You'd also use a few grains of wheat, which you can grab at the local health food store (or supermarket, for that matter) to help kick start things. Don't over do either, as you'll end up with a much more stinky culture as a result.
Trust me on that.
You might notice a scum on the surface, and perhaps a bit of odor to the water...but you're an aquarist, you're used to smelly went stuff, so pay it no mind. And the water will take on a bit of a faint brownish or very light greenish color- totally normal.
After about 4-5 days, you should take a few drops of water from your culture (beneath the "surface scum") and examine them under bright light with a magnifier. You'll be able to see some little, tiny sliver-like things (very scientific) wiggling around in the water. If you're hardcore like me, you'd look at them under your cool hobby microscope (a totally fun tool for the aquarist, BTW) for more accuracy!
This tells you it's time to rock and roll...you can feed your baby Tetras, Barbs, etc. right away, by dropping like 40-50ml of culture solution into your 5 gallon rearing tank. It's actually no big deal if you add more, because these organisms are harmless, and would naturally be found in water with fishes (albeit at a lower density). Feed several times daily, and you'll be surprised how quickly the fry learn to recognize and attack them.
Sure, there is really not all that much involved in the process of raising "infusoria" than we've outlined here. Cultures of Paramecium are used extensively in labs to rear larval fishes, because they are an economical, nutritious option for newly-free-swimming fishes to feed on.
So, like many things in the hobby- the approach may have changed, but the idea remain the same- using whatever means we have at our disposal to create the best possible outcomes for our fish efforts!
I say to the breeder who may, for one reason or another, decided to use different foods- to give the "old school" method a try once in a while, not just because it works- but to help keep alive a direct link to the past of our fish keeping heritage, with a more modern approach applied.
Until next time, watch those little creatures swim, feed those fry...Go old school.
And stay wet.