Live blackworms rank among the best food that you can feed to your fish. Not only are they rich in protein and nutrients, but they can survive for an indefinite periods of time in a freshwater tank – which means that unlike other foods, they will never foul the water and will live until eaten by your fish.
I have personally kept black worms for nearly a decade now, and they remain my go to food for finicky fish. If you have a fish that won’t accept store bought food for one reason or another, then you should always start with offering them blackworms.
I originally started culturing blackworms because my rare (at the time) dwarf puffers weren’t accepting flake, or frozen food. After trying a few other foods that were all soundly rejected, I then moved on to trying blackworms – which were all hungrily devoured (along with the snails I offered shortly after).
One of the benefits to culturing blackworms is that they are one of the easiest live foods to culture. They are also hardier than many of the other live foods, and aren’t nearly as prone to large die offs as daphnia or adult brine shrimp.
Of course this hardiness comes with a downside, and they don’t reproduce as quickly as other commonly available live foods. A blackworm culture will be able to provide a few worms a day for harvesting – but anymore and you will quickly deplete the culture.
There is far from a consensus on the best way to breed blackworms, but it seems that the two methods discussed below result in both stable and prolific blackworm cultures.
Method 1 – Paper Towels
The method most commonly used for breeding blackworms is to use a shallow container filled with narrow strips of paper towels. While this is method is most commonly used in a laboratory setting, it also provides a reliable supply of blackworms for feeding to fish.
To start with, you will need a non toxic container that can hold at least 4 inches of water. Blackworms prefer shallow water, and will do best if they are kept in containers that hold between 4-6 inches of water. In the past I have used plastic sweater containers, or an old 5 gallon aquarium, but it doesn’t matter what you use, as long as won’t leach toxins into the water.
Any water used for a blackworm culture should be treated to remove any chlorine or chloramine and if you have access to it – spring water is often the best choice. Barring access to spring water, aged aquarium water also makes a good choice – as long as it’s from a well established aquarium.
After you have prepared the container and added water, it’s time to add the substrate. For this method you should use brown or organic paper towels. They should be torn into small strips, and added until they cover the entire bottom of the container. Some may have a tendency to float at first, but they should begin to sink after a short period of time.
Depending on the paper towels you use, they should last 10-14 days before they need to be replaced. You can add new strips of paper towels after a water change, and the key is to provide enough paper towels so that the bottom is fully covered.
The water in the container should be changed at least once every two weeks, but for optimal results, you should try to change the water every week. To change the water, simply take the container to a utility sink or toilet, and pour out most of the water – making sure not to lose any worms. Once it has been poured out, you can then add new water to top it up.
It’s also very important to remember that a blackworm culture needs aeration, and you should provide either an air stone or a small sponge filter. While a sponge filter will provide a far more stable culture, without an air stone the culture will likely experience slower growth.
Air stones provide two important functions for blackworm cultures. While its main function is to aerate the water, it also increases the number of worms that break up into pieces – which is how blackworms reproduce in captivity.
It’s extremely rare for blackworms to reproduce sexually in a culture, so the way that they reproduce is through fragmentation. The way that fragmentation works is that a blackworm breaks apart and each fragment grows into a new blackworm. If the fragment is missing a head or tail, they will simply regrow the missing part.
When an air stone is absent, fragmentation rates seem to slow down dramatically, and by extension the population growth. I have had some success using both a sponge filter and air stone, so this may be worth further experimentation to see if you can get the best of both worlds.
Feeding blackworms in this type of culture is extremely easy, and most of their food will be derived from the organisms that feed on the paper towels as they break down. They should be fed very sparingly and a few fish food flakes every few days should be more than enough. Make sure to never feed them until all the old food is gone, as you can easily foul the water if you’re not careful.
Method 2 – Gravel Substrate and Plants
While the paper towel method is an effective way to breed blackworms, it can also be very messy and you run the risk of losing worms during water changes. My preferred method for breeding blackworms is to use a combination of aquatic plants and gravel.
Like the paper towel method, you should choose a container or an aquarium that can hold at least four inches of water and any water that you use should be spring water or treated and aged aquarium water.
The main difference between these two methods, is that instead of paper towels for a substrate, you should use a very thin layer of gravel (only one piece thick) and add several plants. In my experience, this results in a far less messy culture, and tends to be more stable thanks to the plants.
For plants, I mainly use Java moss or water sprite, as both of these do well uprooted and also provide small amounts of infusoria for the blackworms to eat. You can try other plants, but most varieties of rooted plants won’t work in the shallow water provided.
Because there are no paper towels breaking down and feeding the small organisms in the container, you will have to provide additional food in this method. This can be a bit tricky, as the water can foul quite easily, but after a bit of trail and error (hopefully non-catastrophic), you will start to get the hang of it.
The best foods that I have found for this method are half medallions of zucchinis or spirulina pellets. Only use one pellet at a time and any zucchini should be removed after 24-48 hours or it will start to rot and ruin the water quality.
While this is purely anecdotal, I have had far higher population growth in this type of setup. While it may have something to do with the food, it more likely is the result of a greater number of worms fragmenting as they move through the gravel.
Harvesting blackworms is quite simple, and you can use either a pipette, or a turkey baster if you need a large number of worms. Anything else will likely damage the worms, and stay away from anything sharp or hard when harvesting worms.
Any worms harvested should be rinsed off before you put them in the tank, and try to avoid feeding too many worms at once to the fish. If you feed more worms than the fish can quickly eat, they may establish themselves in your tank, and there is nothing that ruins a show tank faster, than hundreds of little worms waving at the bottom.