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 Vinegar eels: New breakthrough in harvesting and other miscellaneous experiments!  

                                                                                                          author: Wayne Schmidt
                                                                                                                 date: 06/21/02


photo courtesy of Wayne Schmidt

 It may sound crazy, but in some ways studying vinegar eels is almost as interesting as watching fry grow. Unlike microworms or baby brine shrimp, vinegar eels are always doing something interesting.

Vinegar eels are an outstanding fry food because they swim throughout the tank, encouraging the fry to swim and in so doing encourage fin growth, and because they are almost a care-free food - unlike microworm cultures that can crash. The one problem with vinegar eels is that they are difficult to collect. In the recent past I developed two quick and easy techniques (please see further down the page) for gathering them but still wasn't satisfied. After several experiments, I developed the following technique which provides an almost continuous supply of small, easily-collected clumps of vinegar eels.

Interesting vinegar eel observations!

1. As a culture's population increases, there is tendency for the eels to collect and crowd together along the upper edge of the growing solution. The worms are constantly wriggling and when their concentrations get high enough, they are forced into such close contact that their wriggling becomes coordinated. They will pack together and wriggle in phase so closely that they begin to look like a single large animal. This in-phase wriggling is very similar to the in-phase, coherent nature of light waves in a laser.

2. Sometimes two groups of in-phase wriggling worms going in opposite directions will meet head-on. When this happens, the pressure at the collision zone can create an area of super-high density where one of three things occurs: The eels bunch up into a tangled knot and this bundle falls to the bottom of the growing solution, Instead of bunching, they form a waterfall of eels, Or the pressure forces a clump of eels upward, out of the growing solution on the sides of the container.

3. After adding vinegar eels to the fry tank, I've noticed that many pairs are joined at the tail. It's not uncommon to see groups of as many as six eels all snagged by their tails and swimming in opposite directions as they try to get away from each other. I assume that eels have a small hook on the ends of their tails that cause them to become connected. This may serve some purpose in mating.

4. The eels aren't able to maintain coherent wriggling in areas where the inside of the tank has been roughened. As a line of wriggling worms contacts a roughened area, they in-phase wriggling breaks down and either the eels form small clumps below the surface or they create a waterfall of eels deeper into the solution.

How to make vinegar eels as easy to collect as microworms! 

Vinegar eels tend to congregate on the surface and at the edge of their containers. As their populations increase, they become concentrated and form long streamers with their bodies, undulating in time with each other as they slowly work their way around the container. The roughened area slows their forward motion down. The worms outside of the area don't know this and continue to push forward. Like tail-gating cars in an accident, they pile up into a tangle and form an easily harvested clump. To do so, I gently dip the collector under the clumps and draw it up while pressing it against the side of the container. A slight rotation of the cloth cylinder with the top moving away from the container's side helps scoop the eels into its surface. The wand is then dipped and swished into the fry tank, releasing hundreds if not thousands of vinegar eels. (I dip the collector into the fry tank first to soak it with clear water. This reduces the amount of acidic solution absorbed when it's put into the vinegar eel container. The small amount of vinegar transferred to the fry tank is so small that it has no effect.)

One caution: the clumps of eels are heavier then water so be sure to avoid bumping the container or the clump will break loose from the side and fall to the bottom.

While the average clump is slightly larger than 1/8th inch across, I've seen them as large as half an inch. After harvesting, another clump immediately begins to form. In as little as five minutes, another clump large enough to harvest is ready to go. I currently have four different cultures set up like this and all of them are producing clumps of eels. Three are producing larger clumps than the fourth and I believe that is because the fourth one was sanded longer so that instead of a roughened area, I created a sanded-smooth area. The key seems to be to roughen without smoothing.

I used a knife to put a few scratches on the inside of the container at the liquid level but that didn't induce clumping. I haven't done any experiments with varying grit sizes or varying the amount of area roughened. I'd suggest only roughening one place. The eels have to have some length to build up enough back pressure to create the clumping force.

A better way to collect vinegar eels:

(...) Instead of swabbing the eels off the side of the culture jar, I simply use an eye dropper to suck the cluster up. I've noticed that eel clusters collected this way result in no damaged eels. It's also easier, faster, and doesn't leave any eels behind.

To keep the amount of vinegar solution collected to a minimum, position the tip of the eye dropper in contact with the cluster and only relax the rubber bulb enough to pull in the cluster. Usually, only a drop or two of vinegar growing solution will be pulled in with the cluster. This small amount of mildly acidic liquid will have no significant effect on the water in a ten gallon fry tank.

photo courtesy of Wayne Schmidt

Usually the clumps are larger but even these few contain many hundreds of eels, easily enough for 100 betta fry. The clumps reform quickly. Ten minutes after harvesting these they had been replaced by a new set of even larger clumps. 

The eels are sucked up into the eye dropper in clumps. If they are simply squirted up into the fry tank, they remain as clumps long enough to fall to the bottom of the tank. Once there, they tend to stay close to the bottom in small areas. This means they aren't disbursed and some fish may discover them and eat most of them before the rest of the fry have a chance to get their full share. A simple solution to this problem is to lightly shake the eye dropper a few times to break up the clusters then drip the contents in several widely-spaced locations. This ensures all the fry have an equal chance at the food.

Three hints!

Hint #1: Have a thimble handy when you use the eyedropper technique (pictured below) to collect eels. Eels collected with an eyedropper tend to be pulled up as tight clumps. If discharged into the fry tank like this, the clumps fall to the bottom of the tank. Since betta fry prefer surface feeding, many of the eels will be wasted. To gently break up the clusters, simply discharge the contents of the eyedropper into the thimble and suck it back up a few times. This separates the eels.

Hint #2: Even separated, drops of vinegar eels still tend to fall to the bottom of the tank because the eels, and the medium they grow in, are heavier that water. This problem can be remedied if there is a horizontal surface just under the fry tank's water line. If there is, discharge most of the eels onto this surface. The eels will congregate there and stay near the surface. But... don't forget to scatter a few drops throughout the tank so that all the fry can find them.

Hint #3: If you use the auto-collecting technique explained below, be aware that after several months, when it's necessary to add some more apple juice to the tanks, that if the new liquid level is higher than the old scratched area, you need to sandpaper the inside of the tank at the new level. Also, it may take a week or more for the eels to start clumping again so only do one tank a week. I redid all five of mine at once and only one of them started clumping immediately. Three of the other four took a week to get started and the fifth took two weeks. Had they all stopped producing, I'd have had nothing to feed my fry.

Apple related climbing experiments...

Note from Faith: Wondering if the amount of apple in the vinegar eel media would affect their ability/desire to climb, Wayne set up several cultures with different apple quantities and different way of cutting the apple:

Having determined my eels grow best in solutions that are mostly vinegar, I then began wondering about the effect of varying the size of the apple pieces on growth. I mixed four identical solutions of 3/4 apple cider vinegar and 1/4 apple juice. One I left as is, the second had 1/4 of a peeled apple added in a single piece, the third had the same amount of apple added after being cut into eight pieces, and the fourth had the same amount of apple after it had been shredded. I stirred up my master culture of vinegar eels, collected one cup of solution, and divided this evenly between the four test solutions, being careful to keep it stirred so that each solution got an equal number of eels.

The fastest growth occurred in the solution with no apple. Next came the one with the apple cut into eight chunks, next the solution with shredded apple, and finally, the one with the slowest growth was the one with the apple left in one piece. There doesn't appear to be a pattern to the growth rate relative to how the apple is cut up.

Four days after starting the cultures, the eels in the shredded-apple, no-apple, and chunked-apple cultures began climbing the walls of their containers. At first it appeared that the more finely shredded the apple was, the more the eels tended to climb. But, after this initial episode of climbing there appeared to be no pattern consistent enough to suggest a reliable way to make eels climb. The culture with a single large apple piece has never had eels climb its wall even after two weeks. But, that may be due to the fact that it has very few eels.

Other climbing experiments...

I also tried using 240-grit (fine) sandpaper to roughen the inside surface of the container with the ideal that a rough texture would make it easier for them to climb. If they are going to climb, they do seem to prefer the roughen areas. But, the presence of a rough area does not seem to encourage them to climb any more often.

The only pattern I've been able to establish for getting vinegar eels to climb is to achieve very high population densities and keep the containers covered. (Please note, my cultures are grown in large, squat containers with one-inch of growing solution and six-inches of air space. This enables the containers to be closed for long periods of time without starving the eels of oxygen.) I confess that I've run into a brick wall as far as inducing the eels to climb on a reliable basis. To make sure I always have some eels climbing so that they can be easily and cleanly collected, I maintain five growing cultures. It's unusual to not have eels climbing in at least one of these when I need them.

Aeration experiment...

To see if providing vinegar eels more air increases the number of worms a culture can support, I added an gently-bubbling air stone to a 1/2 gallon culture. After several weeks of aeration, it appeared that the density of eels was actually less than those in the unaerated cultures. It would seem that the eels require still water to mate.

How many are needed for a spawn? 

Eighty percent of my second spawn's food consisted of vinegar eels. By the end of the fourth week I noticed the eels' population density in each of the four cultures from which they had been harvested had dropped to the point where the eels were no longer forming clumps. (Please scroll down to see how to make them do this and make harvesting as easy as collecting microworms.) Each culture consists of one-quarter of a gallon on growing medium teeming with eels. The spawn only had sixty fry. What this indicates is that to have a reliable supply of eels for a normal spawn (150 fry) that'll last for the 40 days fry will eat them, four times more culture would be required. That works out to about four gallons. Note: this requirement assumes that the vinegar eels will be the principle food with baby brine shrimp and microworms given occasionally as treats. If these other foods are used more often, the amount of vinegar eel medium could be reduced. 


A footnote from Faith:

Once again I am impressed and amazed by how motivated, dedicated, organized and systematic Wayne is in conducting betta related experiments and sharing them with us. We owe him already a lot, because just like most of you, Vinegar Eels have always been a pain in my @#%% when it came to harvest them (or try to LOL). Although I am personally a firm microworms advocate :), I must say that my Vinegar Eel culture has never crashed ONCE since I got it (back in 1998). Super low maintenance, great back up plan. Maybe now that they are easier to harvest, vinegar eels won't have to take the back seat to anyone :), thanks to Wayne.