Nannochloropsis oculata Phytoplankton Culture: Setup, Growth and Harvest

Nannochloropsis oculata phytoplankton culture is different from copepod or rotifier culture in one important way: light is the primary driver of growth, not food. Nannochloropsis oculata is a photosynthetic organism that uses light energy to convert nutrients and carbon dioxide into new cells.

Feeding · Detailed tutorial · About 10 minutes · Beginner friendly

The key habit: Cleanliness is critical with phytoplankton because you are creating an environment where a single species of microalgae should dominate. Any contamination introduced during setup can compete with or overwhelm your Nannochloropsis before it establishes.

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In this guide

What you need before you start
Setting up your culture container
Providing light for growth
Aeration and water parameters
Monitoring and harvesting
Storage and ongoing care
Troubleshooting common issues

1. What you need before you start

Gather before you start

Clean culture container (2–5 liters is ideal for beginners; clear glass or plastic)
RODI saltwater at 1.018 to 1.023 salinity
Nannochloropsis oculata starter culture (your purchased bottle)
Guillard's F/2 nutrient medium, which provides the essential nutrients required for healthy cell division and high-density harvests
Cool white or daylight-spectrum LED strip or fluorescent tube positioned 10 to 15cm from the container
Timer for lighting control
Air pump with airline tubing and air stone
Container for storage (sealed, dark bottle)

Sterilise the culture container before first use. Rinse thoroughly with hot water or use a light bleach solution (rinse very well), then allow to dry completely.

2. Setting up your culture container

1. Fill the container with prepared saltwater. Use RODI saltwater at 1.018 to 1.023 salinity. Measure out 2.5 liters for a standard starter setup.

2. Add F/2 nutrient medium. Add 1ml of fertilizer per litre of culture volume. For a 2.5-liter culture, add 2.5 ml. This supplies the nitrogen, phosphates, trace metals, and vitamins the cells need to divide rapidly.

3. Pour in your starter culture. Use 250 ml of starter culture, giving 2.75 litres of total culture volume. Pour it gently into the prepared saltwater.

4. Set up aeration. An air pump and airline provide the continuous aeration that keeps cells suspended, prevents settling, and supplies the carbon dioxide that Nannochloropsis requires for photosynthesis. A simple aquarium air pump is sufficient for cultures up to five litres.

3. Providing light for growth

Unlike copepod and rotifer cultures, phytoplankton absolutely requires a dedicated light source. A cool white or daylight-spectrum LED strip or fluorescent tube positioned 10 to 15cm from the container, running 16 hours on and 8 hours off on a timer, is the simplest and most effective setup.

Do not place your culture containers on the window—direct sunlight will overheat and kill the culture. Don't use incandescent light bulbs for lighting, as they may heat the culture too much. A desk lamp with an LED or fluorescent bulb works well.

4. Aeration and water parameters

Aeration: Aeration is vital for keeping the algae suspended and ensuring that nutrients and carbon dioxide are evenly distributed throughout the culture. Continuous aeration using an air pump is recommended to prevent settling and promote gas exchange, which maintains consistent oxygen levels.

Temperature: Nannochloropsis oculata will thrive under room temperature, about 20 °C (68 °F) is adequate. Keep your culture away from heaters and cold drafts.

Salinity: Maintain RODI saltwater at 1.018 to 1.023 salinity.

5. Monitoring and harvesting

Week 1–2: Growth phase

Over 5 to 7 days, the water will darken. That's your phytoplankton multiplying. The culture starts pale and gradually shifts to a dark green color.

Harvest timing:

Harvest when the culture is dense, dark green throughout. Don't let it grow too dense, since cell shading, nutrient depletion, and cell lysis (death) all start to set in once the culture peaks.

Harvesting steps:

1. Prepare a clean bucket with fresh saltwater. Fill it with the same salinity as your culture (1.018–1.023).

2. Pour half your culture into the bucket. This creates your new diluted culture to continue growing.

3. Clean the original container. Rinse it thoroughly with hot water (no soap or chemicals).

4. Pour the diluted culture back into the clean container. Set it up again under light and aeration.

6. Storage and ongoing care

Refrigerate harvested phytoplankton at 4–8 °C in a clean, sealed container. Harvested phyto stays viable for several weeks in the refrigerator.

Ongoing maintenance:

Phytoplankton cultures are the lowest-maintenance of the three culture types. The culture looks after itself between harvests. Always clean your culture container between harvests. Never top up an existing culture.

Culture splitting:

Split cultures weekly to avoid crashes. This prevents nutrient depletion and keeps your backup fresh.

7. Troubleshooting common issues

What you notice	What to check next
Culture remains pale after 10 days	Check light intensity and duration; ensure light runs 16+ hours daily
Culture turns cloudy or foul-smelling	Contamination has occurred; discard and start fresh with a new bottle of starter
Water looks orange or brown instead of green	Wrong species introduced; start a new culture
Cells settle to the bottom	Aeration is too weak; increase air flow or check for blocked air stone
Rapid die-off after peak density	Culture was harvested too late; harvest when first dark green, not darker
Foaming on the surface	Harvest is overdue; perform a partial harvest and restart the cycle