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Greater Seattle Aquarium Society

A Can of [micro]Worms

by Dave
April 1997

Are you looking for a cheap, nutritious, easy to grow live food for your baby fish? Then consider culturing your own microworms. A starter culture can be ordered from several of the mail order firms that advertise in the national magazines but the best source is a fellow hobbyist. That’s one of the many reasons to belong to a club such as the GSAS. Microworms are Nematodes, round worms, that live in soil. They’re tiny little buggers about 1-2 mm long, very difficult to see as individuals, but as a mass of writhing worms in a culture container they have a shiny vibrating appearance. One feature that makes them a good fry food is they can live in water for a long time and therefore are available to be eaten over several hours. Due to their negative buoyancy, they sink to the bottom of the tank. This is not a problem for baby Cichlids or other fish that are willing to search the substrate for food, but fish like rainbows whose fry are top swimmers will not benefit from them.

I use oat bran cereal as a culture medium but almost any cereal will do. It does not need to be cooked like the directions on the box state. Just put in one or two tablespoons of dry cereal and add water until you have a runny mix. Let it sit for a few minutes and then add more water if necessary to have a very wet mixture. A tiny pinch of dry yeast can be added but there will be yeast present in the starter culture anyway. Clean yogurt containers or the clear plastic condiment containers that most grocery stores have in the salad bar work well. A few holes are poked in the lid, but not so many that the culture dries rapidly. Transfer 1/2 teaspoon of existing microworm culture to your newly prepared medium and within a few days they will be crawling up the sides of the container ready to harvest.

To harvest, I use my finger to gently wipe some worms from the container sides, trying to avoid getting the media. The tiny amount of media that is inevitable has not proven to be a problem. Then I swish my finger in the tank that has the fry. With a little practice you will learn what the right amount to feed is. I don’t have gravel in my fry tanks so any worms that are not consumed right away will be available and easily found by foraging young fish later. If you are the squeamish type, you could use a watercolor brush to remove the worms from the container, but real aquarists aren’t afraid of worms! I keep the cultures in the fish room where the temperature is about 75 degrees. A new culture or two is started every ten days in order to always have worms ready to harvest and to avoid having it spoil. Inspect the culture every couple of days for mold which will be grey at first, then green, and finally black. Subculture at the first hint of green or you could end up with an angry, festering, seething mass that will impose it’s attitude on your olfactory system, and cause your house mates to freak out. Just kidding, well sort of. I’m just trying to make the point that it is easy to let the culture go bad if you are inattentive. Also, add water if the media starts to look the least bit like it is drying. It should have a pourable consistency.

In reality, raising microworms is very easy, takes very little time to subculture and harvest. Don’t let the fun I had writing this article put you off of trying this excellent fry food. If you let me know, i’ll bring some new cultures to the next meeting.

Dave (another one of GSAS’s longer-running active members) feeds his fish a wide variety of live foods, depending on the season. During the summer, he raises Daphnia and mosquito larvae (much to the chagrin of his neighbors, we bet).