What Are Cyclops?

Cyclops - Adult
Cyclops - Adult. USEPA Great Lakes National Program

Cyclops is a buzzword that is sometimes heard when discussing types of live foods for aquarium fish. Yet many people have no idea what they are, what they are used for, or where to get them. No worries, here is the scoop on Cyclops.

What Are Cyclops?

Cyclops are tiny copepods, or crustaceans, that are found in many freshwater and saltwater bodies of water. They derive their name from the single eye located in the middle of their head.

Another name often used to refer to this tiny crustacean is Water Flea, due to the resemblance of the young Cyclops to fleas found on land.

Cyclops range from 0.5 to 5 mm long, possess antennae, a segmented body, and five pairs of legs. The front section of the adult is oval in shape and includes the head as well as the first five thoracic segments. The rear section, known as a furca, is slimmer and contains the sixth thoracic segment, four abdominal segments, and two caudal appendages that project from the rear. The Cyclops larvae, known as nauplii, are free-swimming and devoid of segments. It is the nauplii that resemble a flea.

Interestingly enough, the body of the Cyclops takes on the hue, at least in part, from what it eats. Cyclops species can vary in color from blue, green, orange, to red. The single eye may be black but is quite often red. They are omnivorous, eating algae and a variety of other microscopic debris, and live on average, about three months.

Females are more abundant than males and have paired egg sacs that are carried at the back of the body. When conditions are ideal, Cyclops will rapidly multiply.

Where Are Cyclops Found?

Cyclops are found in freshwater ponds as well as in slow moving bodies of water. They are often found in the same locations where Daphnia are found.

Cyclops congregate most heavily in the still areas of water that have algae growth. They are also available to fish enthusiasts in frozen or gel based formulas. In warm weather, it is possible to culture them in outdoor containers as live food for fish.

Aren't Cyclops Pests?

In certain cases they can be, so they should be used with a bit of caution. Occasionally they may feast on tiny, weaker fry. Feed very tiny fry on infusoria and freshly hatched brine shrimp initially. Once they have grown out a bit, they can safely be fed Cyclops. Larger fry and adult fish are not in danger from Cyclops.

Outside of the aquarium, Cyclops may be considered pests for other reasons. In some locations and circumstances they can be an intermediary host for disease, including guinea worm disease. This is particularly true in underdeveloped areas with poor sanitation.

Using Cyclops as Food

Cyclops can be fed to fry as well as adult fish, and make a good quality high protein meal. If live cultures are available, they are the ideal form for feeding fish. However, frozen and gel-based products are also good and offer the added benefit of avoiding the possibility that the live Cyclops might feast on very tiny fry.

Livebearing fish, Bettas, Barbs, and Tetras, and even Discus will relish Cyclops as an occasional supplemental food. Bottom feeding catfish will quickly consume any that drop to the tank floor. Cyclops also makes an excellent conditioning food when preparing breeders for spawning. When using gel based product to feed your fish, crumble it rather than dropping the entire gel packet in the tank. Frozen Cyclops cubes can be dropped into the tank unthawed.