Culturing Infusoria for First Foods

How aquarists culture infusoria — tiny freshwater micro-organisms — as a first food for very small fry too small for brine shrimp, with a simple jar method and harvest timing.

What infusoria are

Infusoria is an informal collective term for various tiny freshwater micro-organisms, including ciliate protists such as Paramecium, along with rotifers and small flagellates. They are not a single species but a mixed culture of microscopic creatures that occur naturally in fresh water. Their value to aquarists is their very small size.

Why and when to use them

Infusoria are used as a first food for newly hatched fry that are too small to eat baby brine shrimp. This applies especially to the tiny fry of egg-laying species such as killifish, rainbowfish and many tetras. In the fry-food succession, infusoria are the smallest first food, used before fry grow large enough to move on to microworms or baby brine shrimp.

How to culture infusoria

1. Fill a clear jar with aged, dechlorinated water (tank water works well) and leave it uncovered in a warm, bright spot such as a windowsill.
2. Add an organic medium for the micro-organisms to feed on, for example a bruised or blanched lettuce leaf, a piece of vegetable peel, a little hay, or a few drops of green water as a starter.
3. Wait a few days: the water first turns cloudy as bacteria break down the organic matter, then clears as the infusoria multiply and consume the bacteria.
4. Peak density is reached when the water clears and tiny moving specks become visible; this typically takes about two to three days depending on temperature and light.

A single culture stays productive only for a few days, so experienced breeders start several jars at staggered intervals to keep a continuous supply ready for the fry.

Harvesting and feeding

Harvest by drawing water from just below the surface with a pipette or turkey baster and adding it directly to the fry tank. Feed small amounts often, and avoid adding the decomposing medium itself, which would foul the small volume of a fry tank.