FAST Easy Way to Start an Infusoria Culture for Egg Laying Fish Fry

Infusoria are probably the best first food for really tiny fish fry that hatch from eggs. If you are planning to breed egg layers, they are a must! Infusoria can also be added to daphnia cultures as a source of food for them too.

Start your cultures at least a week before you plan to breed to make sure you have the food ready for your fry. Most fry don't eat the first few days so that will give you about 10 days to get your infusoria cultures well-established.  

What Are Infusoria?

Remember back to grade 6 when you peeked through a microscope to see what lives in a drop of pond water? You probably saw microscopic paramecium, amoeba, green euglena, rotifers, etc. Well, those are what make up common infusoria. They are present everywhere in nature. Their eggs float around in the air and when they land on water with a suitable food source, they hatch, feed and multiply. 

Various species of infusoria are about 25 to 300 micrometers in length. Tiny! Perfect to fit in the mouth of very small egg laying fish when they first hatch! 

Here are 3 common species of single-celled organisms you might see in an infusoria culture. 
60X and 100X magnification

Most infusoria feed on tiny plants (algae), bacteria and even other microscopic infusoria organisms in water. Some, like the euglena, can make their own food using photosynthesis if they have access to sunlight. This is why we put them near a window. To grow them fast, we need to grow tiny plants and bacteria that they eat. In the old days, we were told to put a piece of grass or alfalfa pellet (rodent food) in a container of rainwater and sit that in the sun on a window ledge. Though that still works, today, we know a faster way to culture them.

Infusoria Live in Aquarium Filters
Infusoria are naturally present in any healthy aquarium. You can collect a starter culture by squeezing an established sponge filter or filter sponge or floss from a hang on back filter. You don't need much. Maybe 50ml (3 Tablespoons) per liter (quart) of water. If you don't yet have an aquarium set up, you can get some dirty filter water from a friend in the hobby who has an established tank. Just make sure they don't have any disease in the tank or new fish in at least the past month. 

Use Clear Containers
Place the dirty filter water (starter culture) in a 500mL to 4L clear glass or plastic container. Large mouth pickle jars work well. The wide mouth gives them more surface area for air exchange. I  prefer glass containers so sunlight can get in and are easier to clean. Plastic containers tend to cloud over time and are also harder to clean as they get scratched.

Start Several Cultures at Once
I like to start a few containers at one time, then stagger new ones to have a continuous supply. If you have 7, you can rotate between them every day of the week. If you have many fish fry to feed, then you may want to make more of them or use larger containers. 

Top up the container with clear aquarium water to just before it narrows. This maximizes the air exchange across the surface. It allows oxygen to be absorbed and carbon dioxide to be released.

If you don't yet have an aquarium set up, use rainwater or aged tap or well water (no chlorine) in your jars.

Once the culture has sat for a while, the debris from the filter will settle and you may be able to see a few tiny critters with your naked eye, but it's worth taking a look with a 20X hand lens or a magnifier on your phone or handheld device.

Feeding Your Infusoria
Next, you need to feed the microscopic critters. So far, the best food source to grow a culture the fastest that I have found is a leaf from a cooked Brussel sprout or small broccoli floret. For some reason, members of the cabbage family seem to help infusoria to multiply really fast. I take a frozen Brussel sprout, put it in a mug, barely cover it with water and microwave it on high for a minute. Let it cool and then peel off a leaf and place it in a half to one litre of your culture water.

Just a warning. Using cabbage plants for food give the culture a sulfur smell. It's not very strong and from far away most people can't smell it, but some people with sensitive noses might complain. If you or family members don't like this, either put a lid on your containers making sure there is at least one hole in the lid for air or find an out of the way place to grow your cultures or try using a different food for them.

You can also feed your culture other plant material such as cooked and cooled spinach or swiss chard leaves or thin slices of zuchinni. Dark green leaves work best. Cooking the leaves breaks down the cell walls which allow bacteria to grow faster. The bacteria feeds the culture. 

Is Sunlight Necessary?
Placing your culture in sunlight or under a grow light for a few hours a day will help to grow algae they eat and allow euglena to process their own food. If you don't have a good location with direct light, not to worry, it is not mandatory. Indirect and room lighting will work too, especially if you are feeding them. Make sure the containers won't overheat in the sunlight though. 

Water Temperature and Time 
No matter how you set up your infusoria culture, it takes time for the population to multiply. Temperature can play a factor. Even just raising your containers from the ground to a table can increase the water temperature by a few degrees to speed the growth. You can have a culture ready to go in about 2-5 days at room temperature 20C (72F). On the other hand, if the temperature is too warm, that can slow growth so if you live in a warm place, putting the containers on the floor on cement can help to keep them cool. 

If you don't need your culture but want to store some for later, you can slow their growth by storing them in a small container in the fridge. Just make sure the container is left open for air exchange. 

How Do You Know When The Culture is Ready to Harvest?
A new culture goes through a few steps before it is mature. The first step is that the entire container tends to get milky. This is the bacteria multiplying. That is great since the bacteria will be eaten by the infusoria. The water will start to clear as the infusoria population increases and eats the bacteria. 

After a few days, you will be able to see moving vertical columns in the water. The columns are colonies of infusoria. If you shine a light across the water, you will be able to see the movement.  Many will be moving downward but some will be moving upward too. When you can see many of these columns, the container is mature and ready to harvest.  

If you use a hand lens or microscope, you will be able to see the tiny critters gliding around in the water. 

Here is the view from the top. Can you see the tiny dots? You can see them better by zooming in on the photo your phone. The larger dot at about 5 O'clock is a daphnia by comparison. What we want to focus on is about the size of the daphnia's eye. The oval green bits are duckweed on the surface and the round thing in the middle is a Brussells sprout leaf. The other thing above and to the left of the Brussel sprout leaf (bout 11 O'clock) is an older leaf that has been mostly eaten by bacteria. 

The culture may develop a white scum on the surface. It starts off as a mottled layer. 

Then becomes more solid. It looks like a thin scoby on the top of Kambucha. 

Not to worry, this is likely just a collection of bacteria and infusoria. It is a rich source for starting a new culture. You can either skim this off with a spoon and use it to start a new culture, give it to a friend or dump it in a compost or down the toilet.  The scum can make it hard to see the columns of tiny critters.

Check out my video!

Harvesting Infusoria
Use a turkey baster or syringe to suck up some of the culture water and transfer it to your fry tank. Watch the fry when you slowly drip the culture into the tank to make sure they can find and eat the food.

Avoid sucking up the debris at the bottom of the container as it also contains more infusoria that will rebuild your culture. One you use up your culture, make sure to top up the water with more aquarium water and feed it a Brussel sprout leaf or brocolli floret. As long as there is some plant material in the culture, there will be food for them to eat and they will multiply.

Dried Leaves & Plants Provide a Habitat for Infusoria in the Aquarium
Placing aquatic plants and dried leaves (Catappa, salal, arbutus etc) in the aquarium with the fry can provide an extra surface with biofilm (bacteria) for infusoria to grow on. These infusoria are more accessible for bottom feeders like Corydoras fry and provide extra food for other types of fry between meals. They are also great hiding spots for blackwater fish fry.

To speed the process of growing your culture in the case of an unexpected batch of eggs, you can purchase a starter culture from us

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