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 Quest for the perfect vinegar eel culture

                                                                                                                   author: Wayne Schmidt
                                                                                                                                                         date: 02/11/02


Survey a large number of vinegar eel websites and it becomes apparent that there are as many ways to grow these vinegar eel cultures (nematodes, actually) as there are sites with information on them. Some recommend growing mediums that are mostly water, others insist that solutions containing mostly vinegar are better. A few suggest growing them in the dark, others in the light. A few claim the eels donít need oxygen, others insist they do. The one thing they all agree on is that as valuable as the eels are, harvesting them as food for betta fry is difficult. I decided to conduct some experiments to determine the best growing medium and attempt to develop new harvesting techniques. The results were surprising.

To determine which concentration of vinegar to water induces the fastest, healthiest growth, I inoculated three different growing solutions with the same amount of vinegar eels: 

solution 1 = three parts water to one part apple cider vinegar
solution 2 = an equal amount of water to vinegar
solution 3 = one part water to three parts vinegar. 

Each solution was also given one teaspoon of sugar and a one-cubic-centimeter piece of apple. The cultures were grown in long-necked 12-ounce beer bottles at an average temperature of 70 degrees. 

After three weeks it was clear that the vinegar eels grew best in solution 3, the one-part- water-to-three-parts-vinegar solution. The mostly-water solution had very few worms in it and those that were present acted listless. The number of worms had decreased from the starting inoculation. Also, the solution had an unhealthy milkiness to it that I assume was the residue from decayed eels. The equal-parts-water-and-vinegar solution was only slightly better. However, the number of eels in the one-part-water-to-three-parts vinegar had markedly increased and they swam around with great energy. From this experiment it appears that solutions greater than fifty percent vinegar are to be preferred. However, the fact that many people have had success growing them in weaker solutions suggests that in the long run, vinegar eels may be able to adapt to a wide range of conditions. With this in mind, I suggest that anyone beginning a vinegar eel tank should start with the same growing medium in which their starter culture was raised and repeat these experiments to determine for themselves the best solution.

Two sets of the solutions tested above were prepared with one grown in the dark and the other in a normally-lit room. I could not detect any difference between the two after three weeks. This indicates that light is not a significant growth factor.

While conducting these tests, I observed that the vinegar eels congregated near the surface of the liquid, particularly toward the edge where surface tension curves the liquid up the side of the container. I assumed this preference indicated a desire to be as close to a source of oxygen as possible. With this in mind, I set up a one-gallon, sealed container with a very shallow depth of culture to maximize the amount of surface area available. Vinegar eels in this container appeared to increase faster than in the tall narrow containers of the first test. This lends support to the theory that the eels require oxygen to flourish. I noted that in this container, the eels had a greater tendency to inhabit the entire volume of liquid rather than fighting for room at the surface. I assume this is because the greater surface area permitted more oxygen to be absorbed into the liquid.

I tried the three commonest methods of harvesting and found them all unsatisfactory. Filtering through coffee filter paper was slow and many of the smallest worms wriggled through and escaped. Using various sponges to entrap eels was even worse. Washing the acidic growing liquid out of the sponge lost most of the worms and many of those remaining were damaged. The procedure of lightly corking the narrow neck of a bottle with filter floss then filling the top with clear water for the eels to swim into, thereby washing themselves, works but can take overnight to collect enough eels for a collecting. There had to be an easier, faster wayÖ it turns out there were two.

(1) Take a small test tube, the ones used for testing ammonia levels are fine, use tape to attach a six-inch-long loop of wire or string to the open end below where the cap fits, fill the tube with growing medium siphoned from the area with the densest numbers of eels, cap the tube, and twirl it rapidly around a finger for one minute. Because the eels are heavier than water, they will be forced to the bottom of the tube where their tendency to wriggle will cause them to form a tangled knot. Quickly strain this knot of eels out and add it to the tank where they are needed as food. The knot untangles in 30 seconds to one minute and disperses. This technique works best when the nematode concentration in the test tube is high. A variation on this idea is to fill two tubes with eel solution and tape them to the bottom of a salad spinner. One minuteís spinning produces two clusters of eels that are easily strained.

(2) As quick and easy as the above technique is, the vinegar eels growing in the large-surface-area gallon container presented an even easier solution to harvesting them: vinegar eels climb. Two days after starting the gallon container, I noticed the sides were covered with a fine spider web of thousands of worms. Hundreds could be collected as easily as microworms climbing up the sides of their containers of oatmeal. Regrettably, this behavior is erratic. About half of the time there are enough eels on the side of the container to collect. The other half of the time the sides are clean. Iím currently experimenting to determine how to induce them to climb on a more consistent basis. So far they donít seem to be attracted to or want to avoid light. Tilting the container to wet the sides usually causes them to climb within ten minutes, but this isnít always reliable. If the secret to making them climb can be cracked, vinegar eels could supplant microworms as the food-of-choice for betta fry.

One last experiment I conducted was to test how long vinegar eels live in the neutral PH water of a fish tank. In spite of reports claiming that they live for days, this test showed that ninety percent were dead after only 36 hours. I was careful to avoid any physical trauma and made sure that there was no thermal shock involved that might have shorted their live spans.

A footnote from Faith:

Special thanks for Wayne for all his hard work which is going to benefit all of us betta breeders. :). We need more dedicated betta hobbyists like you!