INFUSORIA – Invisible Food for Invisible Fish

If you wish to raise small fish fry, the very first challenge you will face is feeding them. If you wish to raise fry from fish like betas, guppies and gouramies, you are faced with feeding invisible food to (almost) invisible fish!

The first kind of food young fry of small fish species need is Infusoria. ‘Infusoria’ is an old aquarists term and refers to microscopic life forms that live in all fish tanks, but almost never in large enough numbers to sustain a few hundred hungry baby fry.

It is usually at this stage that the breeder-aquarist grabs at a commercial product called “Liquifry”. Many breeders swear by it, but the truth is that this product is not so much a fish food as it is food for the fish food, because all Liquifry does is feed the infusoria already present in the tank, thus promoting the growth of the small infusoria organisms that fry feed on.

Infusoria are essential for very small fry that, while newly free swimming, are simply unable to feed on larger live foods. Even baby brine shrimp and micro worms may be too large for these very small fry. As a responsible breeder, you do not want this to be a hit-and-miss affair. A good supply of infusoria is therefore needed to help your fry through the first vital days of their lives and make sure that their stomachs are always full. The only way to make sure of that, is by culturing and feeding your own supply of infusoria.

It is not difficult, nor is it expensive, and you do not need a lab coat and microscope to do so!

But let us do the research first!

The images below, taken by Aimee Strickland with a macro lens, give you an idea of just how bitterly small small fry can be!

So, what are infusoria?

It helps to think of infusoria as fresh water ‘plankton’, because that is what it essentially is. Infusoria refers to just about any microscopic, or nearly microscopic organism that lives in fresh water. The list is endless, so I will not name every organism that could be in an infusoria culture, but some of the primary ones include:

  • Algae (Volvox)
  • Amoebas
  • Euglena
  • Paramecium
  • Rotifers
  • Stentor
  • Vorticella.

Infusoria is particularly critical for anyone who is attempting to breed fish, as many newly hatched fry subsist entirely on microscopic infusoria during the early days of their lives. Having a ready supply of infusoria can make the difference between success and failure for an entire hatching of young fry. It also gives your fry the optimal head-start towards healthy growth and development. The most nutritious of the infusoria organisms are the rotifers and ciliates like paramecium.

Where Are Infusoria Found?

Infusoria live in all watery environments — ponds, streams, vases with cut flowers, everywhere water is present. Purified water, such as that purchased in shops and restaurants, is relatively free of such organisms. Municipal tap water is also heavily treated against insuforia organisms. But outdoor bodies of water and even puddles by the roadside literally teem with microscopic organisms/infusoria. It is a world we are not even aware of, where thousands of small creatures eat and get eaten in just one drop of water!

Just so, all aquariums have infusoria — however, we as aquarists perpetually fight the ‘cloudy or green water’ problem in our aquaria. Whenever plankton blooms  make their unbidden appearance in our tanks, and especially in our new tanks, we treat the phenomenon as a problem, instead of a food culture. We change our water, filter and ‘polish’ it, and add a plethora of chemicals, all in the quest for sparkling clean and clear water!

So, it is no wonder that the quantities of infusoria in our tanks are inadequate for raising fry. Hence we have to culture infusoria to feed our fry. However, before delving into how to start your own infusoria culture, it’s wise to know where not to get infusoria.

Where NOT to get Infusoria

It is not unusual for aquarists to be advised to trot down to the nearest pond and scoop up some water to get a good starter culture for infusoria. However, that practice brings considerable risk. The unwary aquarist may be carrying a huge amount of grief home in that little jar of eagerly collected pond water!

In the balance of nature, the undesirables (for us) live cheek by cheek with the good stuff. Out there, all of them are needed to complete the countless cycles of life. But they have no place in our tanks. To name but a few, water tigers, water fleas, damselfly and dragonfly nymphs, hydra, planaria, water boatmen and the larvae of the diving beetle are particularly prolific, and many are quite nasty. Some of these will eat anything they can get a hold of — including your young fish. Even bugs usually considered beneficial in ponds, such as the water boatman, can be dangerous to small fry.

Needless to say, the dangers out-weight the benefits when it comes to taking water from outdoor sources to start an infusoria culture. The best option is to start your own culture indoors, using your own items under hygienic circumstances, so that you can precisely control what is in the end product.

Culturing Infusoria

There are several ‘recipes’ below, but to understand what is involved in, and what  happens during an infusoria culture, let me summarise:

  • The most nutritionally desirable of the planktonic protists are probably rotifers, but the ciliates also provide good nutrition. The most familiar among the infusorian ciliates is paramecium, the “slipper animalcule” you might still 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 all the other non-photosynthesizing single-celled planktonic creatures feed on bacteria that break down organic substances. So to culture them, you need to supply some decaying organic material, temperatures around 28°C and patience enough for the four days it takes for your culture to mature.
  • The requirements for an infusoria culture are simple: a starter culture in water, plus organic nutrients, exposed to strong daylight, but not sunlight and a steady warmth of 28—28.5°C, at a stable and somewhat alkaline pH above pH 7.0. If the water you use is too soft, a shallow layer of crushed coral in the bottom of your container may help to keep the pH above 7.0.
  • You’ll want water that is already rich with abundant founder populations of the organisms you’re after, rather than dechlorinated tap water. The best water comes directly from your tank and it is all the better if it is a planted tank.
  • The starter can be filter-sponge squeezings in the water from your well-established planted aquarium, provided that your tank has not been medicated recently. Otherwise get water from someone else’s tank.
  • You also need to culture your infusoria in a transparent white glass container, with a wide mouth for maximum air/water surface. The reason for choosing glass is that it is easy to clean and also because you can more easily judge the state of your culture. Large canning bottles come to mind, but may not be large enough of you have a lot of fry.
  • The mature culture should be cloudy, but not milky-opaque, with a ripe “pond” odour, but not a foul bacterial stink. Over time, as the culture matures, the smell becomes clean and sweet. Nevertheless, your family will probably want you to keep your culture covered with a sheet of glass or plastic food wrap.
  • Note that culture water that is too rich in organics, combined with not enough aeration, will simply encourage bacterial fermentation, which is not what you want.
  • Many aquarists claim that they get better results with continuous light aeration of the culture, as low oxygen levels inhibit aerobic bacteria.
  • 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. Wilted lettuce leaves left in the dry air till they’re brittle, then crumbled, would be my first choice. But each single recipe swears by what it uses, so the choice is really yours. Nevertheless, exercise some common sense: not all the generally recommended media are what you want or need; non-organic vegetables and lawn clippings may be contaminated with garden chemicals, while banana skins and sliced potatoes tend to encourage a lot of fungus, in my experience. (If I were already running a DIY carbon dioxide set up, I might add just enough filtered yeast culture to faintly cloud the water, since yeast feeds the culture.)
  • As the infusoria grow the water will become cloudy. At first, if you have keen eyes, the infusoria will look like tiny dust particles; somewhat later one can usually see the movement of the infusoria with the naked eye. Examination of a drop of water under the microscope will confirm the growth of the infusoria.
  • Then, as the water of your culture begins to clear, within 3—4 days, the organisms in your culture are at their most numerous. It is time to feed!

Now for the Pro Tip:

Plan for your culture to be ready just after your fry have hatched and absorbed their yolk sacs!  Also, keep several infusoria cultures going while you need them for raising fry, because nothing crashes more unexpectedly than populations of infusoria protists. Also try to stagger the starting time of your cultures, so that you continuously have food to feed your fry.

Feeding and Inoculation

To summarise ahead: There is really no point in feeding your fry until they have absorbed their yolk sacs and are swimming free; you would only cloud their water. Though you will not be able to see what they’re after, feeding fry make very characteristic jerky, dashing motions, and well-fed fry always have bulging bellies. For the fastest, sturdiest growth, you will want to move on from infusoria to nematodes or nauplii as soon as the fry can handle them, feeding both foods for a few days to help the stragglers keep up.

Here is how to feed infusoria:

The trick with feeding from a culture, and/or inoculating a new one, is getting a rich dropper-full of paramecia without too many bacteria. Contrary to popular advice, DO NOT just add the whole culture to the fry tank: it’s mostly water, contains far too many bacteria and often there is a scummy lipid layer at the culture’s surface which you should in particular avoid. You also do not want any of the organic material transferred to your tank. After all, 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.

So, 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 if you have been using it. The resulting lowered oxygen levels through most of the culture will encourage the organisms you want 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 dedicated turkey baster’ (you do have one of those, don’t you?), and fill a tall narrow bud vase. After ten hours or so, you’ll have a clean concentrated layer of ciliate organisms at the top of the vase. With an eye dropper or a syringe (without needle) , you can remove them, either for feeding fry, or of course for seeding a more selective second culture of infusoria.

The first culture you develop, using rich old un-medicated aquarium water, may prove to be less than select. But draw out some culture from the paramecium layer and re-culture that. The result?  Since paramecia multiply so quickly, they will outpace other plankton in the re-cultured medium.

Two Tips here:

  • If you need to filter the water in which you raise fry, use an already functioning (inoculated) sponge filter.  A sponge filter will not suck in your fry, and it also grows tasty rotifers on its surfaces, which is exactly what the fry eat.
  • If you ever need to lower the water level of a tank full of tiny fry, put an air-stone on the end of a length of airline tubing.  Use that as your siphon — incredibly slow, I know, but oh so safe!  No fry will go down your drain.


There are countless recipes on the internet. I would stick to those presented in trusted fish forums. Nevertheless, provided you accept a disclaimer from me for any of these, I have for your convenience  added some recipes below:

Francisco Borrero has this “boiled greens” technique from his mother, a commercial breeder of danios and other egg-layers:

“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 immediately 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 spontaneous innoculation.  Use this 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 inoculate a fresh batch of cooled green water with a small amount of infusoria inoculum taken by pipette 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 inoculum for all succeeding batches. I start a new jar every 3rd day or so, allowing me to have a constant supply of clean cultures. Start with clean jars. Soap residues in jars will result in slow or no culture happening.”

An American recipe:

“Go to the grocery store and buy a turnip. Yes, a turnip. Peel the turnip, cut the white inside part into small 1/2 inch squares. Take the pint of water and drop two of these squares into the water,they will float like ice cubes. Eat the rest of the turnip, they are very healthy and taste wonderful raw. After 5-6 days the turnip pieces will have started to decompose and will be filled with visible infusoria. I take a three cc syringe and put the open tip onto a floating turnip cube and push it gently just under the surface drawing water into the syringe from the side of the turnip. If you take a clear shot glass or similar vessel, and fill it with the water you just gathered from the turnip cube you will see hundreds if not thousands of tiny one celled creatures moving about. Simply dump this into the fry tank a few times a day. Zebra danios can take newly hatched brine shrimp from 2-3 days old and the infusoria will get them off to a smashingly strong start.

On keeping the culture going, just get a second pint jar, fill it with water from the aquarium, put two cubes in it, wait two or three days and draw out some infusoria from the first jar to inoculate the next. You can keep cultures going till the end of time like this.

The advantage of doing it this way is that you will always have a clear culture, no green water, no stink, perfect culture.”

From Wikihow:


  1. The Culture Container. Fill your bottles halfway with tap water treated with a water conditioner that removes chlorine. You must use treated tap water as regular tap water kills infusoria. You may also use water sucked out of a planted tank.
  2. The Culture Medium. Place one lettuce leaf in each bottle.
  3. Infusoria Food. Place one algae wafer in each bottle, you can also try some liquid fry food.
  4. Waiting, waiting, and waiting. Let both cultures sit under bright light for a week or more.
  5. Bacteria vs. Infusoria. When the water is cloudy you have bacteria but wait a little longer.
  6. Finding Infusoria When one culture starts clearing up or turns pink you will have infusoria. The reason it clears up is because infusoria eats bacteria.
  7. Clone Your Best Culture. Pour your good culture into the other culture.
  8. Feeding your fry. Feed your fry a few drops at a time so the tank stays clean. Don’t overfeed, it will make the water green.


  • Siphon water from live plants as they will contain infusoria.
  • Liquid fry food will jump start your cultures.
  • Wash the lettuce well to remove any lingering pesticides, or use organic lettuce instead.


  • Don’t feed until the water clears as it could kill your fry.

Things You’ll Need

  • Rotting lettuce
  • 2 bottles
  • Algae Wafers
  • Bright light

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