Most aquarium related cultures of paramecia are generally referred to as "infusoria". The term infusoria is a collective name for many microorganisms and can include paramecium, microscopic algae, bacteria, protozoans, rotifers, and a host of other small organisms. Unless you are maintaining pure cultures in sterile conditions, your culture will have a mixture of protozoans and algae in greater or lesser degree.
The term infusion animals (animalculæ) was introduced by the German naturalist, Martin Frobenius Ledermüller in 1763, to include all those microscopic animals that appeared in water in which hay had been steeped for several days. This was soon formalised to infusoria by Heinrich August Wrisberg in 1765. Wrisberg described what he took to be the process by which the decaying animal and vegetable matter in infusions produced infusoria. Many of these organisms would originally have been present as spores and cysts, so the infusoria that appeared typically included rotifers and other protozoa, as well as algae. At the beginning of the nineteenth century infusoria comprised a vast array of organisms spanning in size and complexity from bacteria to small invertebrates including worms and crustacea found in lakes, ponds, and streams, as well as in infusions of decaying organic matter exposed to the air. In terms of today's biological classification system, they belong to the kingdom Protista. Protists are neither animals nor plants but in a class of their own. The algae are single celled plant-like protists and the protozoans are single celled animal-like protists.
By far most infusoria are found in fresh water free from actively-decomposing organic matter, rather than in those that contain organic substances in a putrescent state. Their principal importance is as consumers of bacteria. Infusoria feed on bacteria and organic detritus, hence when they present themselves in vegetable infusions, it is usually after decomposition. The decomposing organic matter feed the bacteria, which are even smaller than infusoria. They are not, however, absolutely confined to water; for there are a few species which can maintain their existence in damp mud. Organic materials such as leaves or pond sediment can be collected and added to a container that is then filled with water. In a few days infusoria will have come to the surface, where they can be siphoned off. A tendency of most infusoria is towards the light, and also to the surface.
Infusoria have been used for feeding fish larvae for more than a hundred and fifty years. The procedure adopted by old time aquarists for obtaining a culture of infusoria was by boiling hay, lettuce, spinach or other vegetable matter and allowing the resultant infusion to decompose in the air for a while in the hope that various living beings developed therein. At best this was a hit and miss method and in most cases it simply didn't result in a successful culture. Even if it did succeed, there was always that unknown, unpredictable element of what infusorian would prevail in a given culture, and not all infusorians are equally acceptable as fry food.
"Now the water in an aquarium which has been kept for any length of time necessarily becomes more or less charged with the effete matter of its inhabitants, which if allowed to accumulate, would soon render the fluid poisonous to every living thing within it. This result is happily averted by Infusoria, which feed upon the decaying substance in solution, while they themselves become in their turn the food of larger animals. Thus the presence of Infusoria in the tank may be considered a sign of its healthy condition, although their increase to such an extent as to give a milky appearance to the water is apt to endanger the well-being of the larger, though delicate creatures. The peculiar phenomenon allured to arises from decaying matter, which should be sought after and removed with all possible speed. The whereabouts of such objectionable remains will be generally indicated by a dense cloud of Infusoria hovering over the spot. The milkiness, however, although it may look for the time unsightly, is ofttimes the saving of the aquarium 'stock'. When these tiny but industrious scavengers have completed their task of purification, they will cease to multiply, and mostly disappear, leaving the water crystal clear. I believe it is the absence or deficient supply of Infusoria that sometimes so tantalizingly defeats the attempts on many persons to establish an aquarium." ~ Glimpses of Ocean Life - or Rock-Pools and the Lessons they Teach (John Harper, 1860)
Although infusoria have been cultured and fed to fish larvae for many years, and many fish breeding articles advise infusoria as a first food for fish larvae, there have been very few articles published in the aquarium literature on how to successfully cultivate them.
The best way to bring about a successful culture is to make a vegetable based infusion similar to the above (slices of potato or banana skin works well) using water from a well-established aquarium (that hasn't been chemically treated) or aged tap water. Cultures should be maintained indoors with sufficient daylight (but not sunlight) and kept warm (28°C). Aeration is helpful as the bacterial growth will consume most of the oxygen in the culture, inhibiting the growth of the infusoria. Aeration will also help to reduce any unpleasant odours produced by the decaying organic matter. Within a couple of days the water should turn cloudy with bacteria. Once the culture begins to clear a pale, ever changing cloud of tiny specks will be seen when a glass jar (clear vessel) containing the infusion is held to the light. At this stage you can begin feeding them to your fry.
When the culture is thriving well add a few pieces of vegetable matter, which will provide organic matter when the original culture is nearing exhaustion. The culture will decline rapidly if the nutrients are completely used up. However, care should be taken with the amount added as too much could result in the water becoming depleted of oxygen and cause your infusoria to perish. Culture water that is too rich in decomposing organic matter will simply encourage a bacterial bloom and an unpleasant odour may develop. Generally the culture will settle down again once the bacteria do their work. A healthy culture should be clear and somewhat odourless. A thriving culture can be maintained for months, but it's always a good idea to start fresh cultures occasionally, because nothing crashes more unexpectedly than a population of infusoria. Once you have started a good culture going it is a simple matter to prepare a series of cultures from the original one.
Paramecia
Paramecia are unicellular microorganisms belonging to the phylum Ciliophora. Members of this phylum (ciliates) are characterised by their external covering of continuously beating, hair-like cilia. Under favourably conditions they multiply rapidly by a process called binary fission where they divide in half forming smaller duplicates of themselves. They can also reproduce by conjugation in a similar manner as sexual reproduction in more complex animals.
Paramecia are cosmopolitan organisms and are found in suitable habitats all around the world. Global distribution of paramecia species is believed to be the result of the break-up of the super-continent Pangaea over 200 million years ago. This continent was home to ancestral paramecia that have subsequently been separated by continental drift. The oldest reported fossil paramecium was discovered in a piece of amber dating back to the Cretaceous period, over 65 million years ago.
Paramecia are oval flat creatures, and bear a number of tiny cilia that serve to propel it through the water. As they move through the water they collect small particles of food that are swept into the gullet. Most paramecia feed voraciously on bacteria that accompany decaying organic matter. They are an important link in detritus-based food webs in aquatic ecosystems and are consumed by other small animals, which are in turn preyed upon by larger organisms. Paramecia are an excellent primary food source for newly hatched rainbowfish larvae
The best way to bring about a successful culture is to make a vegetable based infusion similar to the above and introduce a pure culture of paramecia (obtainable from biological and aquaculture supply companies or live food culture dealers). There are a number of different paramecium species available however; Paramecia multimicronucleatum has been found one of the best. It is a very large paramecium and promotes rapid growth of fish larvae. The culture is placed in the infusion and before long a pale; ever changing cloud of tiny motes will be seen when the jar containing the infusion is held to the light. Although just visible to the naked eye, to see paramecia properly, a microscope is needed. Once you have started a good culture of your own it is a simple matter to prepare a series of cultures from the original one. Ideally, you should start a new culture every few weeks.
Feeding
You can collect the paramecia/infusoria with a syringe and feed part of the culture solution directly to the baby fish. Feed the baby fish, according to their number, as often as possible in small quantities so as not to pollute the water. You should be able to tell when the fry are getting enough to eat because their stomachs will be distended.
The best way to collect paramecia/infusoria and avoid adding any of the culture solution into the fry tank is to use a laboratory grade filter paper placed over a funnel and into an empty collection container. Pour the contents of the culture through the filter paper. The filtered medium will collect in the container and the paramecia/infusoria will be concentrated on the filter paper. The paramecia/infusoria are then washed off the filter paper with fresh water and fed to the fry. Return the filtered medium back to your culture container, as the culture will continue to reproduce.
If it is desired to feed the culture to the fry over a predetermined period of time the following method can be used: Drill a small hole in the screw-on lid of a clear plastic food container, the size of some small diameter plastic tubing. Push the tubing through the lid until it is about a centimetre off the bottom of the container. Fasten the tubing to the outside with some sticky tape.
The container is then filled with paramecia/infusoria culture and sited on the lid of the aquarium with one end of the tubing dangling over the surface of the aquarium. The culture is transferred into the aquarium by syphoning and the flow is regulated with an aquarium clamp. By leaving the end of the tubing, on the inside of the container, just above the base less detritus is picked up. Check the water level in the fry tank to prevent possible overflowing when the culture is added.
You can add some water-soluble vitamins to enhance the nutritional value of the paramecia/infusoria a few hours before harvesting. They will absorb them directly from the water. Most vitamin solutions designed for human babies generally contain all the necessary vitamins fish require. You could also use one of the commercial solutions devised expressly for feeding paramecia/infusoria.
© Copyright Adrian R. Tappin
Updated December, 2008.
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