Paramecium are a large single celled bacteria with a body large enough for humans and fish fry to see. With such a large size they are the apex predator of the bacteria world. They eat smaller bacteria which they find as they swim. These smaller bacteria eat decaying vegetable matter. It is a simple food chain to replicate and culture for yourself. Once created the paramecium culture requires little maintenance. This makes them a convenient food source for very small aquarium fry such as Siamese fighting fish.
How To Culture Paramecium
Take some cucumber and shred it with a grater. You can use other vegetable matter which will produce the same affect.
Put the shredded vegetable mash in a bottle and fill the bottle with water. If using tap water de-chlorinate the water or the paramecium bacteria will die.
Take a second bottle and using a strainer pour the liquid from the first bottle into the second bottle.
Keep the mash in the first bottle and refill with water. This bottle will become the food for the culture.
Add some pond or aquarium water to the second bottle. This bottle will become the main culture.
Keep it in a dark place for a few weeks. If kept dark the bacteria wont have to compete with algae for nutrients.
You should observe the liquid change from fairly clear to a little cloudier then clear again over a few weeks. When clear the paramecium should be visible with the naked eye or with a magnifying glass or the naked eye.
Feed the culture with more vegetable liquid when it is not cloudy.
Your food bottle will usually produce it's own bacterial soup and would work fine as a culture itself. The advantage of the second bottle is no clots of rotten vegetable will be transferred to your fry tank from the liquid only bottle.
The main problem with keeping your own paramecium culture is the smell. A foul odor will be created which is at it's worst during the cloudy period. Do not be tempted to stifle the smell by replacing the cap. You must keep the lids off the bottles to let the aerobic culture breathe.
If a scum forms on the top you should shake the culture vigorously. This will break up the floating gunk and replenish the air in the liquid.
Paramecium thrive in acid conditions but you should not need to adjust the water chemistry. The rotting vegetable matter in it's environment will keep the pH low.
Paramecium are attracted to light and will also gather at the top of the bottle if oxygen is low. Siphon them out using a small piece of tubing or a syringe.