Food for fry: Raising Microworms


by Dan Carson (originally written for the Honolulu Aquarium Society )

I consider feeding microworms (Cephalobus) as important as newly hatched brine shrimp and "micro" daphnia to the growth of very small fry. It's also important to culture them in such a way as to make harvesting easy, and clean. Fouling a tankful of fry is a hard mistake to correct. So while the culture method I use for microworms is one I've never seen published, I suggest it because it is easy and clean. Not even a bad smell!

I know the instructions below look difficult and complicated. I did go into great detail. However, if you set up a couple of cultures using this method you will find it's really very easy, and less work that setting up a brine shrimp hatch. It take me about a minute to set up a microworm culture that will produce worms for three or four days!

You will need some small plastic refrigerator type dishes with covers. The "server saver" kind that are made by rubbermaid and sold in super markets are ideal. The brand name isn't important but there should be straight sides at least an inch and a half high...and snap-on covers. You will need some yellow corn meal and some active dry yeast.

Spread about a quarter of an inch of the yellow corn meal evenly over the dry bottom of one of the plastic dishes. It should be dry so you can shake the corn meal from side to side to spread it evenly. Next, it needs to be moistened with water. It's important to just moisten it completely, without adding so much water that it becomes liquid, with puddles. I use a spray from the kind of sprayer that is sold in garden shops for misting house plants. I've also seen a sprinkle cap for bottles used, the kind that people use to moisten ironing.

As I spray the water on, I frequently check the bottom of the dish by holding it up above my head. You can see where the moisture turns the corn meal dark, and just spray the light spots to get an even moistening, without making puddles.

When you have the corn meal completely moistened, its time to add the dry yeast. Sprinkle on enough yeast to cover the surface of the corn meal completely, with a thin layer of yeast. 1/8th of an inch is enough. Because the corn meal is moist, and the yeast is dry, you can shake the dish from side to side to spread out the yeast. If the corn meal moves while you are doing this, you probably used too much water. Get the yeast evenly spread over the entire surface of the corn meal, right up to the edges of the dish, but not up the sides of the dish.

Now it's time to moisten the yeast, using care not to make puddles. Your experience having done this with the corn meal will help. Since you can't look through the bottom of the dish, you have to observe the yeast very carefully here, because a complete moistening, without puddles, is important. When dry, the yeast has a definite sharp granular look. It loses that when moist, and becomes softer in appearance, although not smooth. If it gets really smooth, it probably is too wet.

Now it is time to inoculate the dish with some worms. The neat thing about this method of culturing is that the worms will crawl up the sides of the dish as they multiply. They actually crawl out of the culture medium so you can harvest them from the side of the dish. You simple take a strip of flexible plastic, (I cut pieces from a plastic report cover sold in a stationary store, but you probably have something like it around the house) and scrape the worms off the side of the dish with it. Try not to pick up any of the old culture medium when doing this.

Put a glob of the worms in the center of your newly prepared dish and in a few days they will be multiplying and spreading over the entire surface of the dish. Then they start to climb the walls. (That's why you will want to cover them.) When I feed the microworms, I swish the worms off the plastic scraper into a glass of aged water. I use a tall Pilsner beer glass (the cone shaped glass) and let the worms settle to the bottom. Then I carefully pour off the cloudy water without pouring out the worms, and replace the water with clear. I feed them using a turkey baster. It's very similar to rinsing the salt off baby brine shrimp and feeding it.

I heard that these worms grow best in a cool, dark place, but I keep mine on a shelf right near my fish. They are out of direct sunlight, but in the dark only at night. When the culture starts to go bad, some of it seems to liquefy, and a strong smell develops. After awhile you will begin to start a new culture, before this happens. I use 3 dishes, and rotate them so I always have worms ready to harvest, and never allow them to get smelly. Sometimes stuff comes in the corn meal that hatches out along with the microworms, but this has never been a problem to me because I rotate the cultures frequently. If it's a problem for you, you can cook the corn meal first, and spread the cooked stuff in the bottom of the dish before adding the yeast.

Microworms live longer in a FW tank then brine shrimp. I've seen them wiggling more than 24 hours after they were put in the tank. But resist the temptation to overfeed, because these are a rich food. Mircroworm feeding should be sparing, and alternated with foods like Brine Shrimp and Daphnia to keep the food moving through the fish.