Last Updated: 9/11/08

Cyclops
Daphnia
Euglena
Gastrotrichs
Infusuria
Paramecium
Rotifers
Water Bears

Cyclops are copepods often sold as fish food. These small crustaceans (0.1 inch) eat algae, bacteria, debris and a few species are harmless parasites of fish. Females carry egg sacks which make them easy to identify. They look somewhat like terrestrial sowbugs (isopods, a few species live in water eating rotting plants). The three groups of free-living copepods are calanoid, cyclopoid (the only real cyclops), and harpacticoid.

Daphnia (also called water fleas and cladocera) are often sold as fish food (Daphnia magna and Daphnia pulex specifically). These crustaceans eat algae and microorganisms. They wave their legs around while swimming with jerking motions to bring food to their mouths. They tend to hang out with the plankton and many animals eat them. They are one of the essential species for a healthy pond in many areas since they eat algae and in turn feed the fish. In captivity, they can be raised on yeast, bran flour, or dried blood but algae is best. Looking somewhat like terrestrial fleas, they grow up to 0.1 inch with females giving live birth to tiny babies fit for fish fry to eat. Typical lengths are 0.25 to 3 mm for small species. There are many species, and they vary in size. Daphnia breed both asexually (during good conditions) and sexually (during bad conditions). Females lay up to 100 eggs every three days in good conditions. Females can lay just four days after being born. Her young were developing while she was still inside her mother! If there is a lack of food, oxygen, or space or a drop in temperature, females will lay males. They will breed and produce resting eggs that can dry out just like brine shrimp.

For information on rearing daphnia to feed fish, go to the Daphnia FAQ. A visitor pointed out to me that this site no longer works. If anyone knows where it has gone, please e-mail me!

A drawing of a daphnia can be seen at this water bug site.

I guess no one likes to keep a site with daphnia!

Ok, here is one that someone sent! Thank you!
Daphnia - a site on daphnia as raised as live food for other animals.

And here is a really great site sent to me by its webmaster on 3/4/05:
Daphnia: An Aquarist's Guide

Chuck sent this site on 1/6/06 that he runs on pond life that has a daphnia section:
Pond Info

Euglena are green animals that many larger microorganisms, like daphnia, consume. They are a blob with a tail. Euglena make the water appear green.

Gastrotrichs are microscopic animals that live in bottom debris attached by tail secretions. There are 60 species that live in freshwater where they eat algae. One species is Chaetonotus anomalus.

I have read that infusuria is simply a mix of microorganisms, mostly paramecium. As I get more time, I will look further into this.

Paramecium are animals that look like a blob with many vibrating cilia around it. They are a major food for small fry. They eat smaller microorganisms by engulfing them.

There are nearly 2,000 species of rotifers which differ in their appearance and lifestyles. Some swim, some crawl, some stick onto surfaces using a sort of glue but they all are multi-celled tiny animals with cilia which they use for locomotion and food retrieval. Some eat plants, some algae, some other small animals but all are important foods for larger animals. A few species can survive their water being completely dried out.

Water bears look like bears, except they are only less than 0.05 inches long! Water bears have a head and four pairs of legs with claws. They are also called Tardigrades or moss piglets and their scientific name is Hysibius. They live among plants which they eat. A total of 40 some species live in North America. When the water they are in dries up, so do they. When wet again, they come back to life.
While in the "tun" state, they produce protective chemicals, dehydrate, and roll up. They can exist like this for 1000 years. In this state, they can withstand temperatures from -456 to 304 degrees F, 1,000 times the radiation a human can survive, and 6,000 atmospheres of pressure. Sounds like they may outlive us. (The information in this paragraph was provided by the June/July 1999 issue of National Wildlife.)

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