Cyclops as fish food – is it a good alternative to Artemia?

2024-11-22

As we know from the previous entry on the Raw PetFood blog, Artemia has been immensely popular in aquaculture since the 1930s, with its primary application being the rearing of fish larvae. However, we also know that it is not a perfect feed – for some larvae, Artemia is simply too large, while for others, it may lack sufficient nutritional content. Moreover, Artemia production can be costly and raises environmental concerns due to its harvesting, transportation, and enrichment processes. This is where the authors of an article published in Aquaculture Reports in 2021 step in. They conducted a detailed analysis of another popular fish feed – Cyclops – comparing it to brine shrimp. As it turns out, this small crustacean could be a valuable alternative to the popular Artemia.

What is Cyclops? Origin and Characteristics

Cyclops is a genus of small planktonic crustaceans belonging to the order Copepoda, found in aquatic environments worldwide. The name "Cyclops" originates from their distinctive anatomy – most species have a single, centrally located eye. Cyclops can be found in both freshwater and saltwater habitats, from lakes and rivers to coastal oceanic zones.

The origin and ecological significance of Cyclops

Cyclops are an essential component of plankton, playing a key role in the food webs of aquatic ecosystems. They serve as a primary food source for many fish species and other aquatic organisms. At the same time, Cyclops feed on microorganisms such as algae and bacteria, acting as intermediaries that transfer energy from lower trophic levels to higher ones.

What does Cyclops look like?

Cyclops are small organisms, typically ranging in length from 0.5 to 2 mm. Their bodies consist of a segmented head, thorax, and abdomen, with mobile antennae that allow them to move efficiently through the water. Many Cyclops species demonstrate remarkable resilience, surviving in challenging conditions such as food scarcity, which enables them to adapt to various environments.

The significance of Cyclops in aquaculture

Thanks to their high nutritional value, Cyclops have long been used as feed for fish and other aquatic organisms. They are rich in protein and lipids, including fatty acids such as DHA and EPA, which are crucial for the health and development of fish. Depending on the species and rearing conditions, Cyclops can be particularly beneficial in feeding larvae that require small and easily digestible food sources. It is worth noting the size of Cyclops – several times smaller than the 8-12 mm Artemia, making them an ideal food for fish larvae for which brine shrimp would simply be too large.

Protein and Lipid Content

Research published in Aquaculture Reports has shown that certain variants of Cyclops (Cyclops abyssorum divergens) may contain more protein and lipids than Artemia (Artemia franciscana) – even before being enriched with a properly formulated mix of algae. This is significant because while lipids provide essential energy, especially in the demanding early stages of life, protein is the primary nutrient for living organisms, responsible for their growth and development.

Enrichment of both feeds with an algae mix (Isochrysis galbana, Tetraselmis chuii, Chlorella marina, and Nannochloropsis oculata) highlighted Cyclops' advantage over Artemia in terms of protein content. Thanks to bioconversion processes, Cyclops effectively increased the levels of essential amino acids, such as histidine, isoleucine, and methionine, which are vital for proper fish metabolism but cannot be synthesized by the fish themselves. As a result, Cyclops achieved a more balanced and valuable protein profile compared to Artemia, making it an exceptionally promising feed component for the growing aquaculture industry, where feed quality and efficiency directly impact the health and development of farmed fish.

DHA in Cyclops and Artemia

The level of DHA (docosahexaenoic acid) proved to be one of the most important aspects of the analysis. DHA plays a crucial role in the development of the brain, nervous system, and vision of fish, particularly during the early stages of life. Studies revealed that enriched Cyclops (Cyclops abyssorum divergens) contained significantly higher concentrations of DHA compared to enriched Artemia (Artemia franciscana).

Cyclops demonstrated a high capacity for efficiently converting ALA (alpha-linolenic acid derived from algae) into DHA, effectively functioning as a natural "DHA factory." Interestingly, in the case of Artemia, the opposite phenomenon occurred – Artemia tended to lose DHA during the enrichment process due to their natural metabolic activity.

This advantage of Cyclops in terms of DHA content underscores its potential as a valuable feed in fish farming, particularly for species requiring intensive developmental support during the early stages of life. With high DHA levels, Cyclops can significantly improve the health and survival rates of young fish of various species.

Results in Fish Farming

But did the differences in the nutritional composition of Cyclops and Artemia translate into practical benefits in fish farming? It turns out they did. Researchers conducted an experiment in which European sea bass larvae (Dicentrarchus labrax) were fed with enriched Cyclops (Cyclops abyssorum divergens) or Artemia (Artemia franciscana). The results showed that larvae fed with Cyclops achieved better growth results – they were larger in length, width, and weight. Their survival rate was also higher. By the end of the study, 57.3% of the larvae fed with Cyclops were still alive, compared to only 27.7% of those fed with Artemia.

These results suggest that the higher nutritional value of Cyclops may translate into improved health, growth, and survival rates of fish, making it an interesting dietary alternative in aquaculture. However, it is essential to note that the studies focused on specific strains of Cyclops and Artemia, enriched with a specific algae mix, and one particular fish species. This does not mean that Cyclops will always be the best choice for every fish. The choice of feed should be tailored to the specific needs of the species, its developmental stage, and the farming goals, such as growth rate, health, or survival. Only a comprehensive approach can achieve optimal results in fish farming.

Cyclops as Feed - For Which Fish?

Cyclops is already a well-known and appreciated feed for many species of ornamental fish. Due to its small size, it is primarily used as feed for smaller decorative fish. Below is a list of example aquarium fish species for which Cyclops may be a dietary component.

Golden Goby (Brachygobius doriae)
Bengal Dario (Dario dario)
Indochinese Loach (Syncrossus berdmorei)
Tiger Loach (Syncrossus helodes)
Red Tetra (Tetra czerwona)
Danio erythromicron (Celestichthys erythromicron)
Least Killifish (Heterandria formosa)
Delicate Killifish (Neoheterandria elegans)
Two-tone Labeo (Epalzeorhynchos bicolor)
Guppy, Peacock Guppy (Poecilia reticulata)
Green Labeo (Epalzeorhynchos frenatum)
Microrasbora Kubotai (Microdevario kubotai)
Regan's Julie (Julidochromis regani)
Celestial Pearl Danio (Danio margaritatus)
Malawi Cichlid - Various Species
Angelfish (Pterophyllum scalare)
Altum Angelfish (Pterophyllum altum)
Zebra Pleco (Hypancistrus zebra)

Advantages and Disadvantages of Cyclops

A significant advantage of Cyclops in the aquaculture industry is its ability to be easily cultivated locally, which reduces transportation costs and contributes to more sustainable production. Furthermore, Cyclops reproduce efficiently in controlled environments, eliminating concerns about the impact of harvesting this crustacean on natural ecosystems.

However, using Cyclops as feed in aquaculture also comes with some risks associated with live Cyclops. Other studies have shown that certain varieties of Cyclops can pose a threat to fish larvae and reduce their survival rates (Cyclopoid Predation on Lake Michigan Fish Larvae). Additionally, live Cyclops consume oxygen in the water, lowering overall oxygen levels and potentially creating unfavorable environmental conditions for fish rearing. These drawbacks can be easily mitigated by opting for frozen Cyclops. Frozen Cyclops eliminates the risk of predation and excessive oxygen consumption in the tank while retaining the high nutritional value of live feed.