Microworms (Panagrellus redivivus) are sometimes known under the synonym Panagrellus silusiae and have been cultured by aquarists since the early 1930's as a live food for a variety of fish species. Their small size and ease of culture has received renewed attention in recent years with rising costs and declining hatch rates of brine shrimp eggs sold in the aquarium hobby. Microworm has as good if not better nutritional profile to that of brine shrimp, containing 48% protein, 21% lipids, 7% glycogen, 1% organic acids, and 1% nucleic acids. Approximately 70% of the lipids are fatty acids and the remainder is phospholipids.
Microworms are a tiny nematode about 0.5 to 2.0 mm in length and 0.05 mm in diameter. Males have a curved tail, are smaller, more slender, and less numerous than the females. They reproduce sexually and are livebearers; releasing 10-40 young every 1-2 days for a 20-25 day life span. The young reach sexually maturity in approximately three days. Their size increases by three times during the first day and five to six times during the next three days.
Microworm are one of the simplest live foods to culture. When cultured under the right conditions they will multiply in vast numbers. They are a valuable live food and tolerant of environmental variables. Microworms like it warm and a temperature range of between 25 and 28° Celsius is about right. Although they will tolerate cooler and warmer temperatures, they will not increase in numbers as well. They have the added advantage of staying alive for six to eight hours in freshwater, by which time they should all have been eaten. However, they are not suitable as a first food for all rainbowfish fry; some rainbowfish larvae are so small that they will require microorganisms.
I have cultured microworms for many years and over this period I have tried several different culture mediums. Bread soaked in beer, yeast blends, and a host of other foods. There are almost as many different culture methods for microworms as there are aquarists, each having their own successful anecdote. I will outline some of the more successful methods I have used. What you have to do is find one that suits your particular conditions. Starter cultures are available from biological supply companies or fellow hobbyists.
Microworm can be cultured in almost any shallow, flat, watertight container with a snug-fitting lid. Small holes are pierced in the lid for air circulation. It is a good idea to have at least two cultures running at the same time. Start your second culture one or two weeks after the first. You will often find that a culture will sometimes rapidly decline in production of worms. Having a second culture in production will ensure that you have worms available at all times.
Culture medium can be prepared from almost any cereal grain flour, yeast, and water. However, research has shown that the type of culture medium used has a dramatic influence on worm yields. One such trial was conducted using three mediums - wheat flour, oatmeal, and cornmeal. Yield of worms in wheat flour was significantly greater than in oatmeal or cornmeal. Production of worms stopped after day 20 in cornmeal, day 33 in oatmeal, and day 53 in wheat flour.
The addition of yeast during initial media preparation was found to have no effect on worm yields. However, the addition of yeast on a weekly basis to the wheat flour medium gave a significant greater yield of worms than did untreated wheat flour.
Wheat flour is mixed with water to form a smooth paste and placed in a suitable container. After inoculation with live worms, the addition of 5 ml of a yeast solution, consisting of 7 gm baker's yeast dissolved in 70 ml water; is lightly sprayed over the medium every 7 days. More recent studies on enriched media for microworms has shown encouraging results. Microworm grown on wheat flour plus w-yeast (available from aquaculture suppliers) contained a higher percentage of fatty acids.
Another method is to use rolled oats cereal (porridge). Use one part oats with one part of water. Place the mixture into the culture container and spread to a thickness of 15-20 mm and microwaved on high setting for three minutes. The mixture is then allowed to cool to room temperature. Any media on the sides of the container should be removed with a damp cloth. After the mixture has cooled, place the starter culture on top of the porridge. Within 3-5 days you should see the surface moving. If you use a magnifying glass, you will observe hundreds of tiny worms.
You can increase the production of worms by sprinkling dry yeast powder over the surface of the mixture. You do not have to add the yeast until after about two weeks, then once a week should be sufficient. If the culture medium becomes very watery, you can add a slice of bread to the container to soak up the moisture. The addition of bread has a similar effect as does the bakers yeast.
Yet another method and the one that I now currently use require only a slice of white bread and brewers yeast. This culture method has produced the best results for me. Firstly, cut the crusts off the slice of bread and place it squarely on the bottom of the container. Mix 5 grams of brewers' yeast with ¼ cup of water and pour the mixture onto the bread, making sure that the bread is completely saturated. It is important that there should be very little excess fluid in the container when the container is tilted.
Next add the starter-culture of microworm, by spreading it over the surface of the bread. Replace the container lid securely, and place the container in a warm area. Within three to four days, the culture should be thriving with worms migrating up the side of the container. As the bread is consumed another slice can be added to keep the culture active. After the addition of around 2 or 3 slices of bread the culture will need to be replaced. If the culture becomes too wet, more bread should be added to absorb the excess moisture. Remember the wetter the culture, the lower the production of worms.
During the warmer months of the year I often find another small worm in the culture as well. This is because the odour of the culture will attract the common housefly, which lays its eggs through the small holes of the container lid. The eggs then hatch and the larvae develop and grow on the culture medium. This may seem a little unpleasant to some people, but these worms are ideal for larger rainbowfishes, which love them. Their development doesn't appear to have any detrimental effects on microworm production.
Worm harvesting is a very simple procedure. Wait until the worms are climbing the container walls and you will be able to collect them by running your finger around the walls. If you find this method a little unpleasant, then you can use a small stiff brush. The worms can then be fed directly to the fry by swishing your finger or the brush in the aquarium water. Do not dip the brush in the culture medium to collect worms, as any medium rinsed off into the aquarium will only pollute the water. Another method of harvesting is to lay wooden ice-block sticks on the surface of the culture. The worms will crawl onto the sticks and you can then swish the stick in the aquarium water.
Do not forget uneaten worms will die and pollute the aquarium water, particularly in a small aquarium. If left unattended, it can decimate an entire batch of fry in a matter of hours. To prevent this problem, try feeding the fry three or four times per day in small amounts rather than one or two large ones. In all, microworms offer a cheap, simple and nutritious food for feeding rainbowfish fry.
Microworms can be fed alone or in combination with other foods such as brine shrimp, rotifers, zooplankton, egg yolk, dry diet, etc. Studies of fish fry fed microworms are not significantly different from those fed brine shrimp. A feeding program utilising a combination of food items is better able to meet the nutritional requirements of all rainbowfish fry.
© Copyright Adrian R. Tappin
Updated February, 2007.
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