Now enrich each flask with the appropriate nutrients. Aquaculture Supply sells Micro Algae Grow (catalogue no. FA-MIS, $4.20) for cultivating most kinds of green algae and Liquid Silicate Solution (FA-SS6, $3.50) for culturing diatoms. Directions come with the packages.

The plankton samples arrive in the mail growing in small plastic dishes filled with gelatin. To remove the living cells, submerge the gel beneath a thin layer of your growing solution and allow it to soak for 12 hours. The microorganisms will then easily rub off the gel under the gentle pressure of a sterile cotton swab. Inoculate each flask with about 10 milliliters (two teaspoons) of the resulting solution. Make sure at every step that all your instruments are germ-free by carefully washing them with detergent and sterilizing solution and then rinsing them with distilled water.

Ideally, your culture should be incubated at 19 degrees Celsius (about 66 degrees Fahrenheit), but I had no problems just letting mine sit at room temperature. Avoid exposure to direct sunlight, because the sun's rays can quickly heat your flasks to lethal levels. Instead place the flasks in front of a bright fluorescent lamp for 18 hours a day. A standard bulb of at least 2,500 lumens works fine, but some aquarists recommend "grow-lights," which produce more of the energetic blue photons used in photosynthesis.

Once you start things going, you should keep aerating the water constantly. In about a week, your container should attain a deep green hue, which indicates that the culture is mature and ready to feed to other aquatic creatures. In as few as 10 days, the cellular population explosion can generate enough waste to poison itself, so don't wait too long. If you extract 10 milliliters of mature culture to start a new batch, you'll never need to purchase another starter gel.

The professionals grow larger quantities of algae in 20-liter (five-gallon) containers called carboys. Some scientific supply companies charge $100 for these transparent plastic bottles, but you could just as well use a discarded five-gallon jug from a watercooler. Aquarists usually install a special arrangement of tubing into their carboys to pass the air through without risking contamination. I used a hot-air gun to bend a stiff plastic aquarium tube and achieved the same result [see illustration at left].

Want to grow a lot of plankton? Fill an empty water jug with distilled water or salt water and add five milliliters of fresh sterilizing solution. As before, let things stand for two hours, then dechlorinate the water and test it. Add the necessary nutrients and inoculate the jug with the contents of one complete flask of mature culture. Connect the air pump and make sure the container gets plenty of fluorescent light.

You can track the rate of growth with a special dipstick sold by Aquaculture Supply (AC-DM9, $7.75). Just submerge the stick into the jug until the greenish water obscures the black ring on the bottom, then read the depth off the scale on the side. For each species, you can gauge the density of cells using a table supplied with the stick. After about a week, my water jug had more than 10 million cells living in each milliliter¿some 200 billion cells in all.

With a stable supply of algae, even if it's only two liters' worth, you'll be able to raise rotifers. Although procedures for rearing these sophisticated aquatic predators are straightforward, they are more complex than the simple steps described here for raising their algal food. The interested amateur should consult Hoff and Snell's excellent book for pointers. And keep a lookout for future installments of this column describing amateur research projects that use plankton.

To get your feet wet, Aquaculture Supply sells three complete introductory algae-growing kits: the Maxi Culture Kit (GA-MACK, $77), the Mini Culture Kit (GA-MICK, $48) and the Algae Culture Kit (GA-ACK, $41). Each kit includes Hoff and Snell's manual. As a service, the Society for Amateur Scientists can provide an air filter and a carboy-size stopper for $20. For more information, consult the society's Web site and click on "Forum." You may write the society at 4735 Clairemont Square PMB 179, San Diego, CA 92117, or call 619-239-8807.

This article was originally published with the title How to Rear a Plankton Menagerie.

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