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Dried Flakes or Live Fish Food?
Balancing the Aquarium Ecosystem with Rotifers

Give your aquarium a good, hard look. Does it seem as healthy as a real coral reef ecosystem? Are your fish getting the best nutrition possible? That’s a difficult call to make when many of the critical links of the marine food chain that you’re looking for are microscopic.

Take the lowly rotifer. These tiny, spineless, multi-celled animals are everywhere – in plants, soil, fresh and brackish waters – munching on small pieces of detritus, one-celled plankton and other microbes. They have become an important source of live fish food for aquarium enthusiasts and aquaculture farmers worldwide because:

  • Rotifers have a small, round body that even larval fish, corals and invertebrates can eat.
  • They can be transformed into an even more nutritious food source by enriching the water environment with live protein- and fat-rich microalgae.
  • They swim slowly and stay suspended in the water column.
  • They have a high rate of reproduction.

Though they can’t be seen by the naked eye, rotifers are clearly visible under a microscope. They get their name from the hairs (cilia) on its head that guide water into its jaws and help it swim around. The crown of cilia works in unison so fast that it resembles a wheel in motion; hence, the term “rotifer” – derived from the Latin word for “wheel bearer.”

The cells of rotifers can grow as the organism ages, but are unable to reproduce to make up for dying cells. This is not so critical to this organism, as its life span ranges from six days to three weeks. Female rotifers can reproduce asexually by laying unfertilized eggs when conditions are less than optimal, or sexually when there are ample supplies of food and water available. Fertilized eggs are generally more resistant to drying out than unfertilized ones.

Rotifers are rather primitive in anatomy. Lacking a hard shell or spine makes them an easily digestible food source for slightly larger organisms. A “foot,” acts as a rudder that helps steer when swimming, and as a sticky anchor when sifting for its dinner in nutrient-rich waters. Rotifers are hearty eaters that can pass food particles and microbes through their digestive tracts in 45 minutes!

The most largely cultured larval feed in the world today is the rotifer Brachionus plicatilis. This species’ size and excellent nutritional value (50% to 65% protein) make it the perfect live food for many species of fish fry, corals, anemones, sponges and other invertebrates. This small animal is a necessary link between one-celled phytoplankton and larger copepods, amphipods and brine shrimp. Almost any marine aquarium will benefit from the addition of rotifers and other microfauna!

Not all rotifers are created equal in terms of their nutritional value to fish fry and aquarium invertebrates. Cultures purchased from aquarium food suppliers can vary in density from 200 to 1000 rotifer per milliliter, with most falling somewhere in the middle. Cultures also vary in nutritional quality by what type and how many different phytoplankton the rotifers have been fed.

The most commonly used plankton to feed rotifers is Nannochloropsis oculata, which provides very high levels of EPA (an omega-3 fatty acid). Suppliers of live fish feed often try to skimp on costs by feeding their rotifers only one strain of plankton. The most nutritious cultures are fed a combination of two or more strains of phytoplankton for a complete balance of EPA, DHA and ArA fatty acids. And depending on microalgae growth conditions (lighting, CO₂ supply, nitrogen, etc.), same cells can have higher lipid content than others. So the better the plankton, the better the rotifers and the healthier the fish, inverts and humans who eat them will be.

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