What is Infusoria?: Our Guide

Infusoria is a large, loose basket term that describes all the aquatic micro life that can be found within any body of water. 

It includes things like tiny worms, crustaceans, algaes and plankton that are all living within an aquatic ecosystem.

Some of these tiny animals and plants can end up in your home aquarium or pond; you may spot things living in your tank.

You may see little tiny white bugs or worms swimming around in your tank, (especially if you have a planted tank) and you may at first be frightened, thinking they may be parasites or that they are harmful. We’ll explain what these are, and why you shouldn’t be worried.

Is infusoria bad for fish?

Infusoria is not necessarily bad for fish – there are millions of different species of infusoria; only a few are harmful to your fish and the chances are, the infusoria in your fish tank are harmless.

In fact, many of them can be highly beneficial, especially for a natural planted tank.

Infusoria can actually be extremely valuable for those who breed fish. The tiny animals are the perfect food for tiny fry. Some species of fish are even born so small that they only eat infusoria and nothing else!

Some people even purposefully grow these tiny animals in separate tanks to feed to fry – this is called “Infusoria Culturing” and makes great food for not just babies, but adult fish too.

Infusoria also helps to break down biological waste like rotting plant leaves, uneaten fish food and fish poop. This breakdown process makes waste easier for bacteria and plants to utilise and keeps your water chemistry sound.

Some of these animals however, aren’t always good, and some select few can cause issues for your tank, depending on your situation.

But how do you tell good from bad; what is a pest and what is beneficial?

What types of infusoria are there?

The good, the bad, and the just plain weird

As mentioned, some species of infusoria can be beneficial, whereas others can be detrimental, but which ones are which? What does each one do?

Here is a short list and break down of some common species you may encounter within the freshwater aquarium:

Beneficial Infusoria

Nematode/Roundworm/Detritus Worm

Probably the most common form of infusoria, they are characterised as tiny thin worms that wriggle around. They live within the aquarium substrate and spend their lives breaking down decomposing matter. They aren’t harmful to your fish.


These look like tiny white balls with two antennas which jig around and swim against the glass of your aquarium. These little guys also feed on detritus and are harmless (they are a favourite food of small fish).

Daphnia/water fleas:

These look very similar to cyclops, but are much bigger and have fatter bodies, with little black beads inside them, again, like cyclops. These are harmless and are actually commonly farmed and fed to fish as they are greatly nutritious.


Taking the form of a small shrimp like creature, these could be easily confused with woodlice as they look just like them. They crawl along the substrate eating uneaten fish food, dead plants and fish poop. They are actually quite a good cleanup crew, but will be eaten by large fish if spotted by them.

Seed shrimp:

Tiny crustaceans that live within the substrate and under rocks or wood, they look like tiny kidney beans and scuttle around the floor looking for food. They will eat uneaten fish food or dead fish, but are harmless.

Baby snails:

Baby snails are also considered infusoria as they are small decomposers. Most snail species are beneficial, and are excellent cleanup crew, however, they can breed fast. Some species, like apple snails, eat plants, but most are very beneficial and are harmless to fish and shrimp.

Harmful Infusoria

Brown planaria/flatworm:

These guys look like tiny slugs – they are flat with a spearhead shape with two little black eyes on top and they slither around the tank looking for food. Unfortunately, these guys are predators and hunt for other infusoria and invertebrates.

They will also hunt and heat shrimp, snails and even eat fish eggs, which makes them undesirable.

White planaria:

Very similar to the brown planaria, although a little slimmer and pure white in colour, they are more predatory than the brown planaria and will hunt things like shrimps and snails much more aggressively, although they are still harmless to fish.

How to get rid of harmful infusoria like planaria

If you want to breed your goldfish, have ornamental shrimp or snails, or just dont like worms, there are a few methods of getting rid of harmful infusoria like planaria. They can be a pain to get rid of as they hide well and reproduce fast, but it is possible

  1. The first thing you can do is clean your tank more often.
  2. Give your tank a good gravel clean every week. This will remove the eggs, some worms, and their main food source (detritus). Slowly but surely, this can get rid of planaria.

  3. Chemicals can also be used to kill planaria.
  4. Use these with caution however, as planaria are a mollusc. Every other mollusc, like snails, will also be killed and some will kill shrimp or even fish, so be very careful in your selection.

  5. Traps can also be used and are perhaps some of the safest yet most effective ways to remove flatworms.
  6. We recommend a glass insta planaria trap. It is simple and effective – the device works by placing bait within the trap, the planaria enter the trap and then cant get out, then the trap is then simply removed from the tank along with all the flatworms.

  7. Fish will also eat planaria, given the chance.
  8. This is mostly larger fish or catfishes which are designed to eat them. Cory cats and hoplo cats are very good at eating planaria. Goldfish will also eat them if they spot them.

    How to culture infusoria

    There are many different ways to culture infusoria as they cover different species. In this section, we will stick to those which are the best foods for goldfish and their fry:

    Microscopic Infusoria

    These are the best food for newborn fry.

    They’re not easily visible to the human eye as the organisms are so tiny; to us, it just looks like cloudy water, but to the fish, it is an excellent food source.

    To grow infusoria is quite simple:

    1. Get a jar and fill it with your aquarium water.
    2. Add some boiled cabbage or kale and allow it to stand for 2-3 days (you will notice that the water becomes cloudy; this is the bacteria growing from the rotting cabbage).
    1. Be sure to occasionally stir the jar or add an airstone to provide oxygen.
    2. After time, you will notice the cloudiness will disappear and the jar will become clear. This is the infusoria growing, as the tiny animals are now feeding on the bacterial bloom.

    It may take two or more weeks before an infusoria culture becomes mature and is readily harvestable, so if you are breeding goldfish, make sure your cultures are mature and ready to harvest long before your fish spawn.

    Once your fish are large enough, they can be moved onto crushed up fish flakes and frozen foods.


    Daphnia are very easy to culture and are great for feeding baby goldfish and adults.

    1. First, you will need a bucket or tub or tote, basically anything to hold water.

    2. Fill this with your tank water and leave it outside to collect some algae. You can even throw in a bit of fish food to encourage this. You could also add some dead oak leaves to provide food for the daphnia later on.
    1. Then add some daphnia. These are pretty much sold at any fish store – buy a few packs and add them to your water container, then leave it alone.

      It will take some time for them to begin breeding and growing in number, so leave them for around 2 weeks before starting to harvest from them again.

    Culturing daphnia is best done in the summer where there is lots of sun and it stays consistently warm. During the winter, the colony will die off, but it will come back in spring. 

    The daphnia will continue to feed from the dead leaves and algae that grow in the tote, so feeding them isn’t really required (unless you have a huge colony, then feed them crushed up fish flakes).

    Brine Shrimp/Artemia

    Brine Shrimp are another great food for goldfish, unfortunately, they are a marine creature and are a little more difficult to culture. It can be done though – eggs can be purchased online or in most local fish stores.

    1. Hatch the eggs by filling a container, usually a bottle, with water.
    2. Add marine salt and an airstone to this.
    3. Keep it in a warm place, add the eggs and leave it to stand. 

    Usually the eggs will hatch in around 48 hours, then you can feed the newly hatched artemia to your fish.


    Tubifex, or Blackworms, are very similar to detritus worms. They live in the substrate and are an excellent source of food for goldfish. They can be cultured in a tank with a sponge filter and gravel, and be fed on fish pellets every so often.

    They are fairly easy to take care of, but they are very slow at reproducing, and don’t produce much nutrients for the fish.

    Growing infusoria in a fish tank

    Cyclops, nematodes, scuds and any other microfauna can be easily grown in a planted fish tank. They can be cultured in great numbers if the tank contains no fish.

    A good technique is to have a planted tank setup with no fish, but a running sponge filter, and perhaps a couple snails. Feed the tank small amounts and you will notice over time that the infusoria populations will grow.

    Then you can hatch the eggs or move the fry into this tank and allow them to naturally feed on the tiny animals growing within the tank. This is a really good technique to raise small numbers of fry without having to put in much effort.

    Why is infusoria important to a fish tank?

    As we’ve mentioned, these microorganisms can be really beneficial, but what exactly do they do?

    Well for starters, most of the listed species help to clean up your aquarium by eating and breaking down organic materials, like fish food, plant matter and waste.

    This breakdown process is vital to the filtration of ammonia and nitrites in the fish tank as it is made easier for bacteria to consume. The infusoria produces nutrients for plants too, as they constantly process nutrients through their bodies, in easier forms for plants to consume.

    Infusoria is also the main diet of small fish and aquatic invertebrates, making it the basis for all aquatic life, both in your aquarium and out in the wild.

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