Microworms
Panagrellus redivivus (sour paste nematode)

synonym Panagrellus silusiae (beer nematode) 1

Jim Atchison
The Bug Farm
http://www.livefoodcultures.com 

P. redivivus is a small, free-living (an organism that does not need an intermediate host as in parasites) nematode found in soil. It is closely related to C. elegans, an organism which also frequently studied in science. 

Literature places some confusion on the biology of the organism. Some claim that the nematode is a “self-fertilizing hermaphrodite” with occasional male 2. Other sources state that reproduction is sexual with no mention of the hermaphroditic tendency 3 . However when speaking of the sexual reproduction and male/female traits, mention of males being “less numerous than the females” may be a significant observation within the context of the first (hermaphrodite) statement. However, the source making the claim of self-fertilization is siteing information from the Riddle Lab 6, and that information is referring to C. elegans and not P. redivivus. 

Like other small nematodes (as in “vinegar eels” or Tubatrix aceti), the males have a curved tail and are generally smaller than the females. P. redivivus do not lay eggs and are livebearing. They reproduce very quickly, females birthing up to 40 babies every one or two days for most of their life span.  

P. redivivus  live for several weeks, but not more than a month. They grow quickly to maturity (about 3 days) and reach a maximum size (.45 – 2 mm) in just six days 3. 

There are references that indicate that perhaps the nematodes are somewhat sensitive to light 2, but generally speaking they are not overly sensitive to stimuli. They move by wiggling in a “snake-like” fashion. These nematodes consist mostly of their reproductive system 2, a couple of nerve cords and several small muscle groups. They are what one might refer to as “simple.” 

Commonly referred to as “microworms” in the tropical fish hobby, these nematodes have been cultured by aquarium hobbyists since the 1930s 4. They can used as a substitute for newly hatched brine shrimp (artemia nauplii). As the price of brine shrimp eggs rises and falls on the world market of edible shrimp production, microworms decline and rise in popularity. 

From time-to-time, aquarium hobbyists debate the nutritional value of microworms. Jokes are frequently made that the nutritional value of microworms increases with the increase of the price of brine shrimp cysts.

Other literature, while providing nutritional content information about microworms (48% protein, 21% lipids, 7% glycogen, 1% organic acids, and 1% nucleic acids) 4, do not support the information with references. In a paper for the Journal of World Aquaculture Society, Ricci, Fifi, Ragni, Schlechtriem and Focken  state, “The nutritional value of P. redivivus is high and comparable to that of Artemia.”

While there will perhaps always be some debate on the nutritional values and qualities of this particular nematode, there is little negative evidence to support a negative position and numerous observations and data to the contrary.

The nutritional quality of nematodes can be enhanced by the use of media enrichment or a bio-encapsulation technique. Enrichment is simply carried out by adding a fortification additive (vitamin premix for example) to the culture medium (referred to as direct enrichment). Rouse et al. (1992) used a culture medium which was fortified with a 10% fish oil emulsion, obtaining nematodes that had a significantly higher total lipid content and elevated levels of (n-3) HUFA.

Comparison between the fatty acid composition of P. redivivus non-enriched and directly enriched (expressed as weight % of total lipids) (Rouse et al., 1992).

  Non-enriched enriched
12:0 0.40 0.20
14:0 2.73 4.67
14:1n-5 0.19 1.52
16:0 11.05 12.89
16:1n-7 4.71 10.46
17:0 0.89 0.42
18:0 7.58 4.70
18:1n-9 8.42 15.05
18:1n-7 11.15 11.28
18:2n-6 28.38 9.91
18:3n-3 5.03 9.28
20:0 1.29 0.23
20:1n-9 0.50 1.02
20:3n-3 0.09 0.44
20:4n-6 6.37 4.64
20:5n-3 4.56 7.35
22:0 1.80 0.47
22:1n-9 3.98 1.52
22:2n-6 0.11 0.78
22:4n-6 0.00 0.08
22:5n-3 0.00 0.11
22:6n:3 0.15 3.25

There are very few references in literature to an inferior nutritional composite for microworms when compared to artemia. In one study, where the results of an experiment indicated that the fish given the nematode rather than the nauplli had a slower rate of growth and lower survival rate, the researcher also noted that the result may have been more of an indication of a low density of nematodes during feeding 5. Thus the fish would have starved to death as opposed to not receiving the proper nutrition (a quantity vs. quality sort of deal). 

Other researchers report much more favorable responses from a variety of fish types, including fin fish as well as shrimp. To quote the research of (Watanabe & Kiron, 1994): 

P. redivivus is a suitable larval live food since it is small (50 micons in diameter). Moreover, it has an amino acid profile that matches that of Artemia , while its EPA and DHA content is respectively nearly a third and almost the same or a little higher of that of Artemia.”  

In their supporting data, Watanabe & Kiron, provide data which supports their favorable findings from comparing artemia and the microworm. 

  P. redivivus Artemia
Protein 48.3 61.6
Amino acids    
ILE 5.1 3.8
LEU 7.7 8.9
MET 2.2 1.3
PHE 4.7 4.9
TYR 3.2 5.4
THR 4.7 2.5
TRY 1.5  
VAL 6.4 4.7
LYS 7.9 8.9
ARG 6.6 7.3
HIS 2.9 1.9
ALA 8.8 6.0
ASP 11.0 11.2
GLU 12.8 12.9
GLY 6.4 5.0
PRO 5.4 6.9
SER 3.7 6.7

 

The free-living nematode Panagrellus redivivus is a suitable food source for a first feeding of many fish. A unique method for the mass production of P. redivivus has been developed in fish farming research facilities. The technique involves multiplication of the nematode in fluid culture (fluid media supported by 1- to 4-cm3 sponge cubes). 8

”Two growing media were tested: oat-meal medium, which is an oat-based medium (16.7% oat-meal flour in 0.8% saline solution), and purified ingredient medium, a semi-synthetic medium (1.64% meat peptone, 0.94% yeast extract, 12.6% corn starch, 0.24% glucose, 1.48% sunflower oil, in 0.8% saline solution). “ 8

Ideally, microworms enjoy the same sort of temperature that humans do. About 20-28 C or 70-75 F will find the culture of microworms at it’s peak. There is some flexibility in the temperature, but the further that the culture strays from the ideal, the less productive the culture will be. Just as a matter of “luck,” the microworm (P. redivivus) seems to be a little more heat tolerant than other nematodes 7 . Still, keep the cultures within the range and the culture will be more productive.

Microworms are grown, and do quite well, on a variety of mediums. Many folks use oatmeal as their medium of choice (we do), however, the list of acceptable and successful mediums includes corn-meal, oatmeal, “cooked breakfast cereals”, and instant cereal products (i.e. Gerber Baby Oatmeal Cereal or Gerber Mixed Cereal or Rice or Hi-Protein), wheat, whole-wheat, fresh potato and potato buds. Some folks just use moistened white bread. Mixing the grains and material can also work…but the results may not be significantly “improved” enough to warrant the time and effort. It wouldn’t surprise us if there are more mediums and combinations that work quiet well.

Whatever medium you choose, one will find that yeast plays an important role in the culture process. However, too much yeast will actually create an environment where the culture seems to take on a life of it’s own with enough CO2  to seemingly make the culture want to grow outside of the container. Outside of the medium and the yeast, two critical environmental concerns that these nematodes need to do well are mild warmth and some mechanism which allows the culture to "breath." The warmth can be from placing the culture in a location that will be a little warmer than most (on top of an aquarium is good). The breathing is usually provided by poking a some holes in the top of the container’s lid.

Yes you really do need a lid. Other creatures like to visit microworm cultures and can contaminate the system. The contaminations are probably more of an annoyance that catastrophic. Because the holes in the top need to be small and we have not found just how small the holes need to be able to stop fruit flies and gnats from infesting the culture, we use nylon stocking material (those panty hose with runs in them have just found a new use) and by tying a knot in the stocking and cutting the knotted section away and clipping a short section from the knot of perhaps 3 -4 inches you can make a short “cap” to cover the culture container with the nylon stocking. For larger cultures simply cut a longer cap.

Microworm cultures start to smell as the culture grows beyond it’s maximum (and optimum) productive life. If you refresh the culture with new medium you can both prolong the active life of that culture and at the same time minimize the odiferous culture…they can stink…and we speak from experience(s).

There is some discussion regarding the value of one culture medium over another. Some would venture proof that one is better than another. Frankly, from a practical and hobbyist point of view, any medium will do. These nematodes multiple so fast and in such large numbers. a medium that would be “twice as good” as another would mean that the lesser of the two cultures might produce a mere several million nematodes.  One might find that the amount of yeast added to a culture and the medium itself may have an impact on the aroma wafting through the home, but that is a personal preference. We choose to use oatmeal and make new cultures faster than the cultures can get the point of stench.

If the culture gets too “watery” and it bothers you (it doesn’t seem to bother the worms too much) you can add a slice of bread to the container to soak up the slop. Because the bread will have some yeast in it, the effects are both to soak up the slop and to rejuvenate the culture with food.

A little known notion, yet one that was hinted at in the opening sentences of this paper, is that these nematodes could native to soil environments. We have heard stories that the microworm was discovered in “beer felts” in the early part of the last century, but the critter in question is quiet comfortable in a medium of damp (not wet) soil. While all nematodes are not found in soil, we have tried microworms from various sources and have found that they have all been quite comfortable living in damp soil.

We have kept cultures of these nematodes in soil for months with some interesting culturing and harvesting differences. The soil lends itself to some interesting applications, especially for frogs, newts and salamanders.

The primary difference, other than the dirt of course, is that the microworms are “fed” when they are in a soil as opposed to “cultured” when they are in a starch based medium. This means that one has to put some food into the container from time to time. Time-to-time you say? That is pretty interesting in that time-to-time could mean that you can go for a week (we have), perhaps longer between feedings with no ill effect. The day or two after feeding will find the nematodes congregating around the food blob easily removed with fingers or a spoon and feed directly to a tank or habitat.

These soil-based cultures can also be chilled to slow them down. In effect you can forget about a culture for a month and have little or no care responsibilities, feeding the culture only when you need to harvest.

Oh yeah! None of our soil cultures ever developed those horrible smells of the starch-based mediums.

Unfortunately, the harvest does pick up some soil, which may effect some applications. We were not able to notice any climbing of the wall as with the other medium choices. The production in soil, while very adequate for some needs was noticeably less than in the starch based mediums.

 So how easy it to make up a culture of Microworms? Our method of culturing the microworms is very simple. Mix up a batch of regular, unsalted oatmeal according to the directions on the box. We make ours a little thicker by adding a little more cereal and then cooking it 15 extra seconds in the microwave. Put 1/2 inch of the mixture on the bottom of a butter tub and let it cool to room temperature. The worms live on the surface of the mixture. Deeper oatmeal serves no purposes other that to go bad and smell worse.

Now why do we use those little butter tubs for culturing and not larger containers. In the beginning, we started with butter tubs and we have not found a really good reason to change. We use a “disposable” unit and throw out the culture and the container when it’s finished producing. We have tried a shoebox sized culture and found that it produced way too many microworms for our hatchery of 245 tanks. We are able to manage 4 simultaneous spawns of Bettas with just four rotating butter tubs. We throw the mix out after two weeks and make up new ones. Oatmeal is cheap. We would not compromise our family's olfactory sensations for the price of a little oatmeal.

When the batch cools to room temperature, a small pinch of Fleischmann's active yeast on the top of the mix really makes the mix take off. Don't add too much yeast. Add a portion of a starter to the container by placing a spoonful onto the top of the oatmeal. In about a week you can begin to harvest. After just a couple of days you will probably see part of the mix become more fluid-like and glistening in the light. That glistening is the worms wiggling...the fluid is well...let's not talk about that.

If you don't want to mix the oatmeal, you can use "instant" oatmeal and mix by just adding hot water. We have tried this and it works. It's a little more expensive but faster and makes less mess because you can mix the oatmeal directly in the culture container.

One of our fish friends who raises Bettas uses white bread as a culture medium. It’s a very easy method and requires only a slice of white bread and yeast. She gets fabulous results. You may read that one should remove the crust from the bread, she doesn’t even do that. She puts the bread in the bottom of a container, adds a small pinch of yeast with enough water to moisten the bread. She pours the liquid into the container and over the bread. There is very little extra fluid in the container at the start of the culture.  She then adds a blob of culture from a previous culture and away it goes. When a piece of bread is eaten (by the microworms), she adds another. These cultures seem to last several months.
 

Why don’t we use her method? When you find something that works for you, it is usually easier to keep doing the successful and known process. Really, this is such an easy food to culture any method that works for you is fine. I think that our children might chime in about now with something like, “besides, you can’t teach an old dog new tricks.”     

Harvesting is easy. We use a dull knife or matchstick and scrape the buggers off the side of the butter containers we culture them in. The stick or knife is swished into a beaker with an inch of water in it. After a few scrapes you will be able to see millions (give a take a few) of worms clouding up the water. We use an eyedropper to feed individual fry containers. You can use your finger to wipe the nematodes off the sides also. 

To encourage the nematodes to crawl up the sides of the containers you can use their biology to help you. First, they do need oxygen. Curbing their supply of oxygen will encourage them to seek it by climbing the sides of the culture container. Suppressing their oxygen supply can be as simple as covering the top with plastic wrap or placing a plate on the top of the culture. You can also warm the culture a few degrees. They will then be seeking oxygen in a cooler environment. Don’t think you need to get the culture “hot”…just a few degrees can have a profound effect on the activity of the nematodes. 

For smaller cultures the nematodes can be harvested by adding a small quantity of distilled water to the culture container and decanting the suspended nematodes. 

You may also try filtering them from liquid using a coffee filter. However, the filter/mesh size needs to be in the 100-micron area…much smaller/finer than a coffee filter. A coffee filter may impede a few hundred thousand microworms in the process but you can sure that many times that will probably be washed away.

There are “rumors” that the nematode can be frozen and will come back to life when thawed. While that may be true (can you say “science experiment”?) we have not tried to freeze them. We do however, regularly put extra medium and culture into the refrigerator. The chilling will slow down the development of the culture and has absolutely no effect on the nematodes when they are brought back to room temperature. They will continue their meteoric propagation at room temperature.

Two references have been found that speak to using these nematodes in salt water. As most of the research in the finfish and shrimp farming industries is directed at salt-water environments, this makes sense. In one reference, the reference is merely regarding rinsing the fish in salt water 9. However, in a second reference, the author speaks of the length of time that the nematode can survive in salt water, stating “nematodes can survive for over 72 hours in sea water.” 8

 Once upon a time we put some microworms into a cup of water and at a week threw the water and the still living microworms into the garbage out of boredom. While these may live for a long period of time, they will be at the bottom of the tank and perhaps impossible for the fish to get too. In the case of a gravel bottomed tank, the microworms would fall into the gravel and probably die over a period of time.

We have found these cultures to be very helpful during those occasions where a batch of brine shrimp crashes and the baby fish are crying for their meals. We also use them as a supplement for Betta fry between greenwater/infusoria and baby brine shrimp. After a week most fry are too big for relying on micro worms as a primary food.

We don't normally use microworms as a primary food. The decision has nothing to do with the nutrition debate mentioned earlier, it has more to do with critter's size. These little critters are only slightly smaller than baby brine shrimp. We try to feed any fish the largest food portion that they can comfortably fit into their mouth. We simply don't have too many fish that can not eat baby brine shrimp right away, and the ones that can't need Greenwater, rotifers, paramecium or Vinegar Eels. Therefore we use microworms as an alternate/backup or as a transitional food. One perfect example of an exception for every rule, we break our own rules for using microworms with Corydoras where we use microworms as a primary food for fry and young fish. The Microworms sink to the bottom of the tank quickly and the Cory fry love worms. Even through we don't normally use this as a primary food source we still consider microworms to be a critical element in our strategic food program. We recommend them to all serious fish keepers...not as a universal food mind you, but as part of a comprehensive feeding system.

In a very practical and real sense, these nematodes are so easy to take care of they are about the cheapest insurance one can have against other foods crashing, giving the fish-keeper some degree of control over the nutrition and in some cases the absolute best first food for the fish (or newts or frogs).


1)       
(de Man, 1913) Goodey 1945. Andrassy, I. 1984. Klasse Nematoda. Gustav Fischer Verlag, Stuttgart. http://www.nyu.edu/…/redivivus.html

2)       http://mike-edwardes…net/pr.html

3)       http://edis.ifas.ufl.edu/

Florida Cooperative Extension Service
Institute of Food and Agricultural Sciences
University of Florida
 

4)       Adrian R. Tappin (2000)

5)       http://www.blackwell-synergy.com/…/j.1439-0426.2003.00454.x/abs/

6)       Response of bighead carp Aristichthys nobilis and Asian catfish Clarias macrocephalus larvae to free-living nematode Panagrellus redivivus as alternative feed
By C. B. Santiago, A. C. Gonzal, M. Ricci and S. Harpaz

7)      
Mark Edgley http://biosci.umn.edu/…/wormintro.htm

8)       http://216.239.53.104/…KPcKMVagePsJ:www.genetics-gsa.org/

9)       Journal of the World Aquaculture Society 20, No.2, 61-71. http://216.239.39.100/…/symposium2002/abstract_po/…Panagrellus&hl=en&ie=UTF8

10)   http://www.fao.org/…/W3732E/w3732e0y.htm
FAO FISHERIES TECHNICAL PAPER 361

Edited by
Patrick Lavens and Patrick Sorgeloos
Laboratory of Aquaculture and Artemia Reference Center
University of Ghent
Ghent, Belgium

Reprint Policy: While this document is copyrighted, the author encourages reprinting of the material as the practice may help hobbyists in their effort to captive spawn more fishes. When reprinting the material, please give consideration and credit to the author and send a copy of the publication (or it’s location) to the author. Information on contacting the author can be found on the web site: http://www.livefoodcultures.com

  J. Atchison, 2003, 2009