Culturing Freshwater Organisms
by Thomas Aungst, US
There has been a lot said, at least in the USA, about examining aquatic samples right away when you collect them. Others say that it is best to kill and preserve so that you can study at a more leisurely pace. Unless you have the equipment for field studies you spend an inordinate amount of time running back and forth making collections. Killing and preserving destroys all but the most robust specimens and even then many that remain are distorted by the process.
I prefer a third alternative. Culturing. This allows one to observe a more natural ecology and community history of the life forms in a sample from pond, lake, stream, ditch or puddle.
To culture you need only provide four basic needs:
1) The water for the community
2) Proper temperature
3) Sufficient light
The water would be whatever source you collect from. The proper temperature can be maintained with nothing more than a light bulb placed in a box along with a jar of water with all of those little beasties that you have collected. The light source is the same light bulb that is providing the heat. (See safety footnote).
Proper light and heat are regulated by changing the wattage of the bulb and its placement within the enclosure you are using.
Food ..... Most protists and microscopic life forms, which we term to be animals eat bacteria. So we must provide an ample supply of bacteria if we want our little community to bloom. Now, Mom is not going to be thrilled with our going out to the smelliest part of the nearest barnyard to collect liquid that is full of bacteria. Neither will our wives.
The best, and safest, way to provide plentiful amounts of bacteria is with a tea made from dry hay, straw or weed and grass clippings. Make sure that all plant material has been thoroughly dried before using it to make the tea. The reason for this is that if the tea is made with fresh chlorophyl it will foul the water and ruin the culture.
Boiling up a tea in this way provides you with a sterile food source with which to feed and maintain a rich bacteria bloom which in turn will feed a growing population of protists, which will feed a growing population of multi-celled animals, and so on and so on.
The tea can be placed in a sterilized canning jar and sealed with a tight fitting lid, and kept in the fridge.
If you start with a liter container half full of, lets say pond water with some bottom sediment in it you can add an ounce of tea as needed. Give the culture at least 24 hours and the check a drop of water, taken from the surface, under the microscope for the presence of bacteria.
If you do not have a lively bacteria population within 48 hours add another ounce of the tea and check again and repeat if needed. Add more tea 1 ounce at a time as needed to maintain a flourishing community of protists and algae.
DO NOT add too much tea or the culture will go foul. If the jar gets full siphon off about 1/3rd of the water and keep going.
I have maintained viable communities like this in 1 gallon loosely sealed jars for over 20 years.
Comments to the author Thomas Aungst welcomed.
Be especially careful when using mains powered lights near water. Ensure the wiring is properly insulated and metal objects are correctly earthed and keep well away from the water. Also ensure that the container will not overheat and catch fire.
Published in the October 1999 edition of Micscape Magazine.
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