If you have fussy feeders in your tank, offering them live foods can often be a very effective way of persuading the fish to eat when they tire of frozen foods. Unfortunately, the live food that you can buy in your local fish store often comes with a few unwanted extras in the form of bacteria or parasites that can harm your fish.
But your fish can still benefit from the nutrients and proteins that live foods contain if you culture your own live food, such as blackworms. Blackworms can survive indefinitely in your tank, meaning that they won’t pollute the tank water. And you know that there’s always a source of food for your fish, so they will never go hungry.
In this guide, we explain how to set up and manage a blackworm culture. But first, let’s find out more about these fascinating creatures.
What Are Blackworms?
Blackworms (Lumbriculus variegatus) are also commonly known as California blackworms. Blackworms can be found across North America and Europe, inhabiting shallow waters, including ponds, marshes, and swamps.
This type of freshwater worm can grow up to 4 inches in length and feed on organic detritus and microorganisms. They have a distinctive forked head section and are usually dark brownish-red to black.
Although blackworms can reproduce sexually, they generally do so through an amazing process called fragmentation. That means the worms simply break into fragments, each growing a new head and or tail and becoming a new separate worm.
Blackworms are extremely popular in the hobby, as they make a great food source for aquarium fish. The worms are very rich in fats, proteins, and vitamins, making them an excellent addition to the diet of breeding fish and growing fry.
Are Blackworms Harmful To Humans?
No! Blackworms are not harmful to people at all. However, we recommend that you always wash your hands thoroughly after handling these creatures, especially dead worms.
Do Blackworms Bite?
No! Blackworms do not bite people.
What Do You Feed A Blackworm?
In the wild, blackworms feed on tiny microorganisms and general detritus. So, they will do the same in an aquarium environment.
You can feed your cultured blackworms with sinking fish food flakes every few days. Ensure that the blackworms eat what you’ve offered them to avoid overfeeding them and ending up polluting your fish tank. If you’re using the paper towel method, use organic paper towel strips. They will feed on the bacteria that grow there.
Blackworms can survive on very little food, but the more you feed them, the faster they’ll grow.
How Fast Do Blackworms Reproduce?
If provided with the correct water conditions and kept at room temperature, blackworms will thrive and breed readily, roughly doubling in volume every four weeks or so.
How To Start A Blackworm Culture
The method you use to culture your blackworms depends a lot on how intensively you plan to harvest them.
If you intend to culture blackworms as an occasional treat for your fish, you can simply grow some in a 5-10 gallon aquarium with shrimp or herbivorous fish. However, if you need an abundance of blackworms as a staple food, you’ll need to set up a dedicated blackworm aquarium since intensive cultures produce a lot of waste.
What You’ll Need
To start your culture of blackworms, you will need the following:
- A fish tank or plastic food storage container, depending on how many blackworms you want to produce.
- A layer of gravel or sand to cover the bottom of the tank to roughly an inch deep.
- A sponge filter or corner filter that will work in less than 6 inches of water.
- A starter culture. You can usually get some blackworms from your local fish store or order them online if not.
- Some organic compounds that you can feed the worms. Blackworms will eat anything. However, you shouldn’t feed them diseased fish, as that could cause an outbreak of disease in your tank.
- A selection of immersed, low-light plants. Low-light aquatic plants are the best choice, as blackworms are less active in bright light conditions. Plants help keep the water clean, and the worms will graze on the dead plant leaves and infusoria. Java Moss or Water Sprite are good choices.
- A clear-sided turkey baster that you can use to harvest the worms.
Setting Up Your Blackworm Culture
Once you’ve assembled everything you need, you can go ahead and start breeding blackworms.
Choose a site for the culture
First, you need to decide where you want to keep the culture. Blackworms don’t appreciate rapid temperature changes, and they can’t survive below freezing. Also, a blackworm culture is not the most attractive thing in the world, so it’s probably better to keep your blackworm tank out of sight of your display tanks in your living room.
Set up the tank
Once you’ve chosen a spot, add the sand/gravel and filter.
Fill up the shallow water tank with dechlorinated water or spring water to a depth of not more than about six inches. You can use aged aquarium water from another aquarium as well. Use a shallow container so the worms will get more oxygen. However, if you want to keep a deeper tank, you can use an air stone or air pump to oxygenate the clean water for the worms
Just like most aquatic organisms, blackworms are sensitive to ammonia and nitrites, so you need to let the tank cycle, or else ammonia will build up extremely quickly and ruin your water quality.
Preparing your starter culture
Once the tank has cycled, you can go and get your starter culture.
Starter cultures are sometimes refrigerated, so don’t plunk them into the tank immediately. First, warm up the worms slowly in the air until they reach room temperature.
Once they have warmed up, pour a scoop of blackworms into a small container. Cut the worms in half and then in half again. Within a few hours, the worms will regenerate tails or heads or both, which jumpstarts the culture’s blackworm population.
Introducing your starter culture
After you’ve cut the worms, you can drop them in the tank and feed them.
A good diet of sweet potato slices, old fish food, or spirulina pellet food works well, along with plant trimmings and dead leaves as additional food. After a few hours or less, you should see the worms clustering around the food you’ve added, tails in the air, and heads buried.
If they start trying to climb to the surface, that means they need more oxygen and fresh water. In that case, you should increase aeration and possibly reduce the water level.
How Do You Harvest The Blackworms?
Harvesting blackworms is a relatively simple process.
You can use either a turkey baster or a pipette to harvest the blackworms. Simply suck the worms directly into the device you’ve chosen. Don’t use anything sharp or hard that could damage the delicate worms.
Once you’ve harvested the worms, you need to rinse them off and remove the dead blackworms before feeding them to your fish to eliminate any clinging detritus.
Be careful that you don’t give your fish too many worms in one sitting. If you overfeed the fish, the worms will disappear into the aquarium gravel substrate, where they will most likely establish a colony over a period of time. Although that does mean there’s a ready supply of blackworms for your fish, hundreds of little worms waving at you from the tank bottom are not the most appealing sight!
A Few Things To Bear In Mind …
- Blackworms will fragment and reproduce on their own with no intervention. However, if you want to speed up the process, simply collect a cluster of worms, cut it in half, and then return the worms to the culture bin.
- Food will sometimes start rotting in the tank. Rotten food is absolutely fine, as the bacteria produced by the decomposing organic matter feeds copepods and also the blackworms.
- Sometimes you’ll find little leeches living in your blackworm culture. That’s also not a problem, as your fish will eat these, too.
- Copepods will abound in your culture tank! If you reduce the oxygen in the water, the copepods will swarm at the surface, where you can collect them and use them as fry food.
Blackworms make excellent live food for your fish. The worms are packed with valuable nutrients, vitamins, proteins, and fats perfect for conditioning breeding stock and feeding newly hatched fry.
Starting a blackworm culture is very simple and is the safest way to give your fish a live diet without the risk of introducing diseases and parasites, which sometimes happens when you use commercially produced live foods.