Vinegar Eels

Choosing foods for your newly hatched (free-swimming) fry can be very challenging. While some species of fry will accept powdered or prepared foods, most species of fry need food with the “wiggle factor” of live food to encourage them to begin eating. Without a doubt, the most universally used live food for new fry has to be newly hatched brine shrimp, but if the species of fish you have chosen to raise are very small such as Rams, Danios or Killifish, the problem of identifying live foods small enough to be eaten by newly free-swimming fry can be very challenging.

While there are quite a few food s available for this task, most have some drawbacks, IE: smelly, messy, difficult to harvest and feed, etc., and unless you raise a lot of fry, the cultures can be difficult to maintain. Then we found Vinegar Eels! Vinegar Eels (VEs). Vinegar Eels are free-living, non-parasitic, un-segmented nematodes. While sounding gross, they are unbelievably easy to culture and feed. The proof of this statement is that my wife will allow us to keep them in the house! Keeping them cannot be simpler. They eat the bacteria that grow in unpasteurized vinegar solutions. In fact, the only downside that we found is that your fish room may smell like a fresh garden salad for a couple of days when new vinegar is added! In addition to their tiny size, the other advantage that they have over many other live foods is that they will stay alive in fresh water for up to a week. That means that over-feeding your fry is not a problem, as the eels will not die and foul your water.

VEs live an average of 10 months, giving birth to as many as 45 young every 8-10 days. A healthy culture can experience a 20-times increase in its population in only 8 days! It may sound like you will quickly be overrun with vinegar eels, but they are so tiny (the young are nearly microscopic), that there is no danger of your culture being overpopulated any time soon. They thrive over a wide range of temperatures from 60-90 degrees, and can easily be maintained in you current fish room without refrigeration or any special care. In pure liquid cultures (like the one we use) over 90% of the VEs will inhabit the top ¼” of the liquid, as they need to be as close to the oxygen rich surface as possible. In a newly established culture, you will see them as a thin “scum like” substance forming around the edge of the container, right where the liquid at the top meets the sides of the container.

The beauty of these critters is that they require almost no effort on your part.  Cutting up the apple slices is the hardest part of the process.  Our “master cultures” routinely last for 6-9 months before they need to be “overhauled.” In fact, the only maintenance you need to perform is to add a little aquarium water every couple of weeks to replace any liquid that has evaporated, and to add a couple of apple slices every 3 months.  I have to admit, after a few months, the jar looks disgusting with all the crud on the bottom, but the eels are so thick, you can't see through the jar.

From the research we’ve done, the "experts" (I’m not exactly sure who would designate themselves as a nematode expert) claim that the eels are not very nutritious and should not be their sole food for extended periods of time.  Our experience with them has shown that by day 3 or so (after free-swimming) the fry are typically large enough to eat the regular Great Salt Lakes baby brine shrimp (bbs).   After the batch of fry we’re feeding has moved on to bbs, there are typically a large amount of eels left in the harvest jar.  Just pour them back into your culture jar and move that jar to the back of the rotation.  Simple!

Like any live food, the use of VEs requires a little prior planning. Don’t wait until you have fry to begin thinking about finding a first food for them. Even though VEs multiply rapidly, you really should start your culture at least 4 weeks before you plan to have fry. As we said, VE cultures don’t go bad, so if you have them sitting around for several months, they will still be OK.

Starter cultures of Vinegar Eels can be found on E-Bay for a couple of dollars, or if you bought your fish from us, we would (and have) sent out starter cultures for the cost of shipping.


Starting Your Own Vinegar Eel Culture

The size of the container you use is up to you. It really doesn’t matter. We use plastic, one gallon size containers (actually food-grade canisters) that we purchased from Wal-Mart for our “master cultures.” These are actually the same containers that we use for hatching the eggs as well (see photo 1). We also use quart-size canning jars (Mason Jars). If you are only planning on raising a batch or two of fry, then the quart size would be more than sufficient. If you are like us, and have a lot of little mouths to feed, then maybe the gallon-size would be your best option.

VEs need to breathe, so don’t put the lid on tightly. You can either set the lid on loosely (plastic jar), or remove the center lid from the canning jar, stretch a piece of cheesecloth over the mouth of the jar and screw the retaining ring back on. For a more permanent lid, you can silicone a small piece of screen in the outer ring (see photo 2).

For your starter culture, you will need:

  • Culture Jar
  • 50% apple cider vinegar (non-pasteurized)
  • 50% apple juice
  • Several slices of apple (skin on or off doesn’t seem to matter, but everyone always asks).

As soon as you mix the ingredients together, you can add the vinegar eel culture. Store the container at room temperature, and out of direct sunlight. We put ours on a bookshelf. After 2-3 weeks there will enough vinegar eels in the container to start harvesting them. That’s all there is to it! No baby cereal, instant potatoes, no yeast. And best of all, no foul smell!

After a couple of weeks, you'll notice some white scum forming around the edge of the culture container.  If you swish the container, you'll see what appears to be chunks of scum break off and slowly sink to the bottom.  That's not scum. That is tight knots of adult eels.  If you look closely at the chunks sinking, you will see the adults wiggling around and start to separate from the knot.  They will eventually swim back to the top and the process starts all over.  If you have any doubts about the whether your culture is growing, just put a flashlight behind the culture jar.  You should see millions of little eels wiggling like crazy, but they're so small, they look like dust particles in the water. The ones you will be able to see are the adult eels wiggling like crazy, but the smaller ones, (the ones your fry eat), are so small you won't even be able to see them, but they're there. 


Harvesting the Eels

OK, so now, you have a good culture going strong, the big question is “how do I harvest them to feed my fry?” There are a lot of different ways to do this, but most are difficult at best, and do not give good results. Once again, the answer is so simple, that I’m surprised that it’s not common knowledge. To harvest the eels for feeding, you will need:

  • A clear, long neck bottle (12 oz or more) with fairly wide shoulders and long, thin neck. We use a quart size Olive Oil Bottle (see photo). Not only is it the right shape, but the heavy duty glass keeps the bottle from shattering when I inevitably knock it over. A clear Corona beer bottle also works (and it’s more fun emptying the beer bottle than the olive oil bottle).
  • A 12” section of monofilament fishing line. Thread will work too, but you will probably have to replace it more often.
  • A golf ball size wad of polyester filter floss.
  • Aquarium water (de-chlorinated)


Putting It All Together:

  1. Run the bottle through your dishwasher to makes sure it’s completely clean and sterile.
  2. Remove the lid from your culture jar, and using a funnel, (you’ll thank us later), pour the contents into the bottle until the liquid just reaches the point where the neck of the bottle begins.
  3. Fluff up the piece of floss and tie the 12” piece of fishing line around the floss. The string is only used to remove the floss later for cleaning. Again, you’ll thank us when you don’t have to try and fish out the floss with your fingers!
  4. Wad up the floss, and push it into the neck of the bottle. Then using a pencil or pen, push the floss down to where it just touches the liquid at the base of the neck.
  5. Fill the neck of the bottle with aged aquarium water. You should stop when the water level is just below the first thread at the mouth of the bottle. Remember to use aged (de-chlorinated) water for this step. Chlorine is added to the water to kill the very organisms that you are trying to grow. If done correctly, the floss will form a distinct barrier between the vinegar and the water. Vinegar, being denser than water, will stay below the level of the (floss) water as long as you don’t shake it up. At this point, the culturing solution will be cloudy, and the water will be clear.
  6. VEs need oxygen to survive. To get to their air supply, they will swim up through the wad of floss, and will rise into the water column in the neck of the bottle. (That’s why a long, thin-necked bottle is best). After an hour or two, you’ll be able to see some eels swimming in the clear water above the floss. For the best results, set up the harvesting bottle the night (12 hours) before they are actually need. The next morning, the water in the neck of the bottle will appear very milky. Those are the eels! To harvest and feed your fish, just use an eye dropper or similar device to suck up some of the water containing the eels, and squirt it in the tank with your fry. Because of the density of the vinegar, it will not mix with the water, so when you feed your fry with this method, you will only be adding clean vinegar eels and aquarium water into your fry tank. There is no chance of contamination from the vinegar! Remember to add a little aquarium water back to the bottle to replace the water you sucked up and squirted into your tank. That’s all there is to it! As more and more of the eels pass through the floss, the culturing solution will become clearer and the water becomes cloudy with eels. When both the water and the solution become relatively clear, the supply of eels has been depleted.

This is absolutely, the easiest way to feed small fry that we have ever found. Depending on the density of your culture, there should be enough vinegar eels in a one quart harvesting jar to feed an entire span of rams for a week. Once you have reached the point where your fry are able to eat larger food, you can simply pour the remaining vinegar eels back into your culture jar, pull out the floss (We told you you’d thank us for the fishing line) and pour the contents of the harvesting bottle back into the culture jar, put that lid back on and wait until the next spawn.

With a new batch of rams, we will feed them a small quantity of VEs at least three times a day, and we also add a tiny bit of baby brine shrimp. Even though the majority of the fry will not be able to eat them, there may be a few that can handle newly hatched bbs from day one. And, as the fry begin to grow, the bbs will supply them with a more nutritious source of food as soon as they are large enough to handle it. In our experience, it is only necessary to feed rams VEs for the first 3-5 days after free-swimming. Usually, by day 3, most of the fry will be able to eat bbs, and you will be able to see their swollen pick bellies, signaling that they have made the transition to bbs.

TIP:  Rather than using a one gallon container for your culture, try using four one quart mason jars instead, and use a one quart bottle for your harvesting bottle. When it comes time to harvest the eels, simply pour the entire contents of a one-quart culture into the harvesting bottle. When you are done feeding a batch of fry, simply pour the contents of the harvesting bottle back into culture jar and rotate it to the back of the line. When it’s time to harvest the next batch of eels, simply grab the next jar, and you will have a fresh culture to use. Continue moving the “spent” jars to the rear of the line and you’ll always have a fresh batch of eels ready to harvest.


Photos Coming Soon!