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Microworms and Walter worms

Update coming soon....after reading a very interesting article about these in the Journal of the American Killifish Association, I tried these on potato flakes, which work quite well, but were a bit more prone to serious stinkage at times, so I am back to my baby cereal cultures.

These are very small, but at 1-2 mm long, are visible as tiny threads in the water when you feed them to your tanks.  The fry of most fish can take these soon after hatching:  they're considerably smaller in diameter than even newly hatched baby brine shrimp.  They do fall rather quickly to the bottom of the tank, though, so top swimming fry may not get enough of them.  I've had two different varieties that are available locally, and now only keep so-called "Walter worms".  These are a type of microworm that spend more time in the water column before they sink than do regular microworms (click here to see an experimental demonstration of the difference).

I cultivate these on a mix I learned from Al Andersen's talk on live foods at the MASI show in 2003:  gerber instant oatmeal or mixed grain cereal plus a bit of brewers yeast plus a little instant dried yeast (about a pinch of instant yeast plus a tablespoon of brewers yeast to a cup of cereal).  I think the worms are supposed to eat the live (activated) yeast, which feeds on the cereal and brewers' yeast.  I make this up in bulk and just add equal parts mix and water to a clean dish, so that it is a thick paste like this:


I place a dollop of this in a small plastic container, and add a few drops of liquid from an earlier culture.  As the culture matures, it will get thinner and darker , and that is normal.

After reading a very interesting article about these in the Journal of the American Killifish Association, I tried these on potato flakes for the first time a few weeks ago, and they worked great, but the smell got nastier quickly, so I have gone back to the baby cereal.  I now do it simpler and add the cereal mix to the container and water to that, without using an intermediate step of mixing it up in bulk in the bowl.

After about a few days to a week, the worms start crawling up the side of the containers.  The cultures are harvested daily by wiping the worms off the side of the container with a finger and kept going until the yields drop, usually for about 3 weeks.  I looked through the cheap disposable containers at the grocery store to find some that I could stack in a small container, because the easily harvestable worms come from the sides of the container, as here above the red line:

microworms closeup

where I rub them off daily with my finger to feed the fish (you can use a rubber scraper or a popsicle stick for this part if you're squeamish, or your hands are dirty):

worms on fingers

There are more worms living in the lower part of the culture, but harvesting them leads to putting a lot of cereal debris in my tanks.  So I prefer to use multiple small containers, here trying to get the maximum amount of side-wall surface for harvesting.  Yogurt containers and margerine tubs are often used, but I found some little disposable cups that fit stacked in a box so they're easy to handle.  I poke holes in the lid with a pushpin for air exchange, but be sure the holes are small or fruit flies can find their way in (very very messy).  These worms do fine, by the way, whether they are kept in a light or a dark place.

under sink

After swiping the wall of the container, I swirl my finger in a clean cup of water.  Then I rinse the worms through a brine shrimp next to get rid of the cloudy cereal debris.  I swirl the containers daily to recoat the sides of the container after I take off the worms, which seems to encourage the worms to climb up the sides for easy harvest.  When the culture turns darker and fewer worms come out, despite being stirred/swirled daily, I dump it and start a new one, usually every 2-3 weeks.  There are typically 2-3 fresh, 2-3 medium, and 2-3 older cultures going at any one time, and still I don't get very many worms at once, but fortunately the little fish that need these don't need a lot of them to grow .

Walter Worms

Sometimes a little skin of yeast or bacteria grows on top of the culture, but does not harm the worms, and the flakes of it that end up floating on top of the water are easily poured off before the worms are poured into the net for rinsing:

filmy worms

If you don't see lots of worms on the side of the container, don't despair.  They're probably still in there.  If you swirl the culture and look at the surface closely, it should look like it is moving or bubbling, like this:


Looking a little closer up (this requires a magnifier) you start to see the individual worms swimming at the surface

closeup microworms
And here they are climbing up the wall of the culture:

wirns ib wall

Jack noted that stirring some puffed rice cereal (not rice krispies, but puffed rice) into an older microworm culture can keep it going for weeks more. 

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