Copepods eat microalgae, bacteria, and tiny animal prey, but the best food to offer depends on the species you’re culturing and why you’re growing them. Most hobbyists and breeders get the best results feeding a mix of live phytoplankton species, supplemented with other organic matter like fish food flakes or yeast. A single algae species will keep copepods alive, but a varied diet produces larger populations that reproduce faster.
What Copepods Eat in the Wild
Copepods are not strict herbivores. In nature, many species are omnivorous or even primarily carnivorous, feeding on ciliates, bacteria, and other microscopic animals alongside microalgae. One study of the calanoid copepod Acartia hongi found that tiny animal prey (ciliates and heterotrophic dinoflagellates in the 20 to 100 micrometer range) accounted for more than 70% of the carbon the copepods consumed throughout most of the year. Phytoplankton only dominated their diet during winter diatom blooms, when it made up about 60% of their intake.
This matters for culturing because it tells you copepods do best with nutritional variety. Feeding only one type of algae can sustain a population, but you’ll see better reproduction and survival when the diet includes protein-rich and lipid-rich sources that mimic the diversity they’d encounter naturally.
Best Phytoplankton Species for Copepod Cultures
Live phytoplankton is the foundation of most copepod diets in captivity. The most commonly used species, roughly in order of popularity among aquarists and hatcheries, are:
- Nannochloropsis: A small, hardy green alga that’s easy to culture at home. Rich in EPA, one of the two key omega-3 fatty acids. A good everyday staple.
- Isochrysis galbana (T-Iso): A golden-brown flagellate prized for its high DHA content. DHA is the other critical omega-3, especially important if you’re raising copepods as food for fish larvae.
- Tetraselmis: A larger green alga with a good overall nutritional profile. Works well for bigger copepod species that can handle larger food particles.
- Thalassiosira (diatom): Diatoms are especially valuable for harpacticoid copepods like Tisbe. Cultures offered a diet including Thalassiosira diatoms produce larger and more reproductive Tisbe populations.
- Chaetoceros (diatom): Another diatom commonly used in hatcheries, with high EPA levels.
- Rhodomonas: A cryptophyte alga with an excellent balance of both DHA and EPA. Often considered one of the best single-species feeds for calanoid copepods.
The key takeaway: no single algae species provides everything. Diatoms like Thalassiosira are rich in EPA but relatively low in DHA. Dinoflagellates and species like Isochrysis are high in DHA but lower in EPA. Mixing two or three species covers both fatty acids and gives your copepods a more complete nutritional profile.
Feeding by Copepod Type
Harpacticoids (Tisbe, Tigriopus)
These are the copepods most reef aquarists culture. They live on surfaces, crawling along rock, glass, and substrate rather than swimming in open water. Tisbe biminiensis and Tigriopus californicus are the two most popular species. Both are relatively unfussy eaters. Tigriopus in particular is remarkably tolerant of different food types, with research showing its development time stays roughly the same regardless of which microalgae species it’s offered.
For Tisbe, the best results come from microalgae with the highest protein and lipid content, which translates to more offspring per brood and more nauplii overall. A mix of Nannochloropsis and a diatom like Thalassiosira or Phaeodactylum tricornutum works well. You can also feed powdered spirulina, small amounts of crushed fish flake food, or reef phytoplankton blends sold at aquarium stores. In a reef tank, Tisbe will graze on biofilm, detritus, and any phytoplankton you dose into the water. If your tank is very clean or newly set up, dosing live phytoplankton occasionally helps keep them fed.
Calanoid Copepods (Acartia, Parvocalanus)
Calanoid copepods are free-swimming and filter feed from the water column, so they need suspended food rather than surface biofilm. They’re pickier and harder to culture than harpacticoids. These species do best on a diet of small flagellate algae like Isochrysis, Rhodomonas, or Nannochloropsis kept in suspension. Calanoids generally feed on particles smaller than what harpacticoids prefer.
Because calanoids are primarily used in aquaculture hatcheries to feed fish larvae, their nutritional quality matters enormously. The goal is copepods packed with DHA and EPA. Feeding a mix of Isochrysis (for DHA) and a diatom (for EPA) is standard practice. Interestingly, copepods appear to assimilate fatty acids more efficiently when their food contains lower concentrations of those fats, suggesting that moderate, consistent feeding outperforms heavy dosing of nutrient-dense algae.
Non-Algae Foods That Work
You don’t need a phytoplankton lab to feed copepods successfully. Several accessible alternatives work, especially for hardy harpacticoid species:
- Yeast: Nutritional yeast or baker’s yeast suspended in water provides protein and can sustain copepod cultures short-term. It lacks the essential fatty acids of microalgae, so it shouldn’t be the sole food long-term.
- Fish food flakes: Finely crushed marine flake food, sprinkled sparingly into the culture, breaks down into particles copepods can consume. This works especially well for Tigriopus.
- Powdered spirulina: Inexpensive and nutritionally dense. Mix a tiny pinch into culture water. A little goes a long way.
- Reef Roids or coral foods: Powdered coral foods contain fine particles of marine-origin nutrients that copepods will eat.
- Biofilm and detritus: In established aquariums, harpacticoid copepods feed heavily on the bacterial film that coats surfaces. A tank with good biofilm may not need supplemental feeding at all.
How Much and How Often to Feed
Overfeeding is the most common mistake in copepod culture. Uneaten food decomposes and produces ammonia, which is far more toxic to copepod larvae (nauplii) than to adults. Research on Acartia tonsa found that nauplii showed negative effects at ammonia concentrations as low as 81 micrograms per liter, while adults tolerated levels roughly 20 times higher before showing harm. Half of exposed nauplii died within 72 hours at just 220 micrograms per liter.
The practical rule: feed small amounts frequently rather than large amounts occasionally. For a phytoplankton-fed culture, add enough algae to give the water a light green or tan tint. When the water clears, the copepods have eaten it, and you can add more. If the water stays colored for more than a day or two, you’ve added too much. For dry foods like spirulina or crushed flakes, use less than you think you need. A pinch the size of a few grains of salt for a one-liter culture is a reasonable starting point.
Monitoring water clarity is your simplest feedback tool. If the culture starts to smell foul or the water turns cloudy rather than tinted with algae color, ammonia is building up. A partial water change and reduced feeding will usually correct it. Weekly pH checks help too, since ammonia becomes more toxic at higher pH levels.
Boosting Nutritional Value for Fish Larvae
If you’re raising copepods as live food for fish fry or coral, the fatty acid content of your copepods directly reflects what you feed them. Copepods fed diatoms accumulate high levels of EPA, while those fed dinoflagellates or Isochrysis accumulate more DHA. Fish larvae need both, so the standard enrichment strategy is feeding copepods a blend of at least two algae types for 24 to 48 hours before harvesting them.
Diatoms and dinoflagellates complement each other almost perfectly in this regard. Thalassiosira diatoms contain roughly 26 to 30 micrograms of EPA per milligram of carbon but only about 5 micrograms of DHA. The dinoflagellate Heterocapsa triquetra flips that ratio: around 29 to 37 micrograms of DHA but under 2 micrograms of EPA. Feeding both gives copepods access to the full spectrum of essential fats that developing fish need.