Have your fish gone and laid eggs? Congratulations! You’ve proven yourself capable of not only helping fish to live but thrive in your aquarium! Babies are right around the corner – but caring for them can be much trickier than caring for adults.
Just like people, baby fish can be very picky eaters. Even the smallest of flakes and frozen foods can be too large for them! How are we to feed such tiny fry?
What are Infusoria?
If you’ve ever given some thought to breeding your fish and raising live food for the young fry, you’ve probably come across this term before. Infusoria is a catchall term for the microscopic or near-microscopic organisms found in aquatic environments.
This includes single-celled algae, parameciums, amoebas, and all of the other familiar faces from high school biology class. Weirder looking organisms include rotifers, stentors, and all sorts of other microscopic predators and prey.
Here’s a look at Infusoria under the microscope!
Why Should I Grow Infusoria?
So as interesting as the microcosmos is, as aquarists, why should we care about Infusoria? Because they are the perfect starter food for many young fish!
If you’ve raised Guppies and other livebearers, you were almost certainly rewarded with small yet relatively well developed fry. Large, free-swimming babies are a huge advantage – this is why Guppies give live birth in the first place. They can dart around and will eat powdered flake, brine shrimp nauplii, and other relatively large items early on.
Many other aquarium fish, such as Bettas and Gouramis, have tiny, helpless young. When born they hang out in their father’s bubble nest for a few days, passively snacking on microscopic prey until they grow enough to swim freely and eat larger items.
With such small fry to feed, Infusoria are a valuable resource to have on hand. Unfortunately, pet stores don’t typically carry it! What are we to do then?
How to Culture Infusoria
Fortunately you don’t need to rely on your local store because Infusoria are incredibly easy to raise yourself! You’ll need to gather the following supplies:
- 1 medium to large jar (a mason jar works well)
- Enough aquarium water to fill the jar ½ way
- A light source. A nearby window with ample sun is ideal as the full spectrum light will fuel green algae and bacterial growth. However even a desk lamp placed overhead will provide light and heat.
- A small piece of decaying vegetation. Anything can do the job but kitchen scraps are perfect. Some pieces of potato peel, leftover celery, or material from the crisper you never quite got around to using…Feel free to be creative.
- An aeration stone & air pump (recommended).
- A thermometer.
First, you’ll need to place the jar in a well-lit location and add aquarium water to it. Any mature aquarium already has colonies of infusoria. However, there’s rarely a lot at any one time and usually not enough to feed young fry.
Before adding the vegetation, give the jar an hour under direct sun or the lamp and check the temperature with the thermometer. If temperatures get much higher than 85, make an adjustment to the light source by finding a spot that gets indirect sun, direct sun only a few hours per day, or raise the light source higher.
Infusoria like warmth. But too much heat will fuel bacterial growth and kill many Infusoria species.
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Once you’re certain the temperature range is ideal (65-85F) add your kitchen scraps. You won’t need to fill the jar, a 3-inch section of potato peel or even some clippings from dead aquarium plant leaves will do the trick.
While some Infusoria species do feed on decaying vegetation what we’re actually after is a bacterial bloom. Infusoria much prefer feeding on bacteria – and on other Infusoria!
While not 100% necessary, adding an aeration stone will keep anaerobic bacteria at bay. These microbes create toxic wastes that inhibit the growth of other organisms and smell particularly foul.
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The last step is time! Within a few days to a week the jar should turn either cloudy (mostly bacteria & Infusoria) or green (cyanobacteria or algae & Infusoria). If you have time, I recommend waiting a few more days for Infusoria to continue feeding and multiplying.
Typically the water will clarify as the Infusoria begin to eat most of the bacteria or algae. However if your fish fry need to be fed ASAP, feel free to dip into your colony right away!
Upon close inspection you may even see tiny free-swimming Infusoria. Some of the largest paramecium and amoebas are barely visible and you may even get microworms and other multicellular organisms. All are fine food for baby fish!
Can I Collect Infusoria in Nature?
Some aquarists no doubt live near ponds and other bodies of still water rich in organic matter. These are natural breeding places for organic, free-range Infusoria! But should you use wild Infusoria to feed your fish fry?
I strongly recommend not doing so because as stated earlier, Infusoria is a catch-all term for creatures that are larger than bacteria or viruses but smaller than the majority of animals and plants. Not only are some of them inedible or toxic but many are predators themselves!
Hydra are a classic example. As Cnidarians they are freshwater cousins to Sea Anemones, Corals, and Jellyfish. And like their larger relatives, Hydra have long stinging tentacles that snare and kill passing prey.
Many fish fry are small enough to be a meal for one. Worse, once Hydra get a foothold in an aquarium they can be nearly impossible to get rid of.
Outdoor ponds also contain disease-causing organisms like infectious bacteria and worms. You may also accidentally scoop up micro predators like dragonfly larvae, which find fish fry absolutely delicious.
While raising Infusoria is a topic rarely discussed in aquarium circles, it’s the best way to feed the smallest fish fry. They get quality live food identical to what they’d be feeding on in nature. And an Infusoria culture can be ready for harvest in just a few days – perfect for those times when your fish surprise you with eggs! If you’ve had success with raising Infusoria, feel free to tell me what tricks work for you!