Why Live Food Cultivation is Necessary
Most marine fish hatch as planktonic larvae, and at this stage their mouths are extremely small (approximately 0.1–0.3 mm), capable of recognizing only moving microscopic creatures as food. Frozen foods and artificial diets are unsuitable for larval stages, and it is impossible to keep the fry alive without supplying live food.
When attempting to breed many popular marine fish species such as Ocellaris Clownfish, Sergeant Major, and Flame Angelfish, establishing a live food cultivation system becomes the first hurdle. This article explains the three-stage live food cultivation system that breeding professionals actually use.
Growth Stages of Marine Fish Larvae and Required Live Foods
| Larval Age | Mouth Size | Suitable Live Foods |
|---|
| Immediately after hatching – Day 3 | 100–150 μm | Nannochloropsis (phytoplankton), SS-type Rotifer |
| Day 3 – 2 weeks | 150–300 μm | S-type Rotifer, Copepod Nauplii |
| 2–4 weeks | 300–600 μm | Adult Copepods, Finely Ground Brine Shrimp |
| 1 month onwards | 600 μm and above | Artemia (Brine Shrimp) Nauplii |
Providing an uninterrupted supply through these three stages is the lifeline of successful marine fish breeding.
Step 1: Culturing Nannochloropsis (Phytoplankton)
What is Nannochloropsis
Nannochloropsis (Nannochloropsis oculata) is a microscopic alga with a diameter of 2–4 μm. While larvae may feed on it directly, its primary purpose is as food for rotifers. Adding it to tanks as "green water" also helps reduce stress in larvae.
Basic Culture Setup
What You Need:
- Clear plastic bottle (2 L) or sealable polycarbonate container (5–10 L)
- Seawater (specific gravity 1.020–1.023, sterilized)
- Nannochloropsis starter culture (available through online retailers or aquarium shops)
- Fluorescent or LED light (daylight white, 5,000–6,500 K)
- Air stone + air pump (gentle aeration)
- Liquid fertilizer (marine-grade F/2 medium is ideal; commercial trace element solutions like Hyponex can be used as alternatives)
Culture Procedure:
- Add 10–30 mL of starter culture to 1 L of sterilized seawater
- Add liquid fertilizer at the recommended dose (for F/2 medium, 1–2 drops per mL)
- Maintain under fluorescent light (12–16 hours daily) with gentle aeration
- Within 3–5 days, the color deepens to green (a sign of increased cell density)
- Harvest half, and for the remaining half, add fresh seawater and fertilizer to propagate the culture
Management Tips:
- Optimal temperature is 18–24°C (too high and the culture easily crashes)
- Avoid direct sunlight (risk of temperature rise and bacterial contamination)
- If the culture becomes too dense (turning yellow-green to brown), light cannot penetrate and the culture will collapse; thin it regularly
- Culturing multiple bottles in parallel spreads the risk
Step 2: Culturing Rotifers
Types of Rotifers
The rotifers used in marine fish breeding are Brachionus plicatilis, classified by body length as follows:
| Type | Size | Primary Use |
|---|
| SS-type (Ultra-small) | 100–120 μm | Newly hatched larvae – small-mouthed fry |
| S-type (Small) | 150–200 μm | Staple diet for most marine fish larvae |
| L-type (Large) | 200–300 μm | Developed fry and megalopa stage |
For beginners, it is easiest to start with S-type (or universal) starter culture.
Culture Setup
What You Need:
- 10–20 L plastic bucket or container
- Seawater (specific gravity 1.010–1.020; culturing is possible at lower salinity)
- Rotifer starter culture
- Nannochloropsis (as food)
- Moderate aeration
- Temperature control (20–28°C)
Culture Procedure:
- Add 10 L of sterilized seawater to the bucket
- Add 100–200 mL of rotifer starter culture
- Add nannochloropsis once or twice daily (maintain a pale green color)
- Density begins to increase the next day, reaching harvestable levels (500–1,000 individuals/mL) within 3–5 days
- Harvest 30–50% daily and add fresh seawater and nannochloropsis to continue the culture
Harvesting Method:
Use a plankton net (50–100 μm mesh) to filter and drain the water, or use a homemade net made from nylon stockings. Rinse the harvested rotifers in clean seawater before use.
Advanced Technique: EPA Enrichment
When rotifers are cultured on nannochloropsis alone, their nutritional profile becomes imbalanced. To achieve higher larval survival rates, treat the rotifers with commercial enrichment products (such as Selco or DC DHA Selco) for 1–2 hours before feeding to boost essential fatty acids like EPA, DHA, and arachidonic acid. This step is essential for breeders aiming for commercial-scale production, such as with Ocellaris Clownfish.
Step 3: Culturing Copepods
The Importance of Copepods
Copepods have higher nutritional value than rotifers (particularly in DHA and EPA) and are the most important natural food for marine fish larvae. They are indispensable for maintaining difficult-to-feed species such as Mandarin Fish.
The primary cultured species are Tigriopus californicus (Tigriopus) and Tisbe biminiensis (Tisbe), with starter cultures available online.
Culture Setup
What You Need:
- 10–20 L polycarbonate tank (polycarbonate construction is preferred)
- Seawater (specific gravity 1.023–1.025, similar to main tank)
- Copepod starter culture
- Nannochloropsis (primary food) + commercial phytoplankton products (supplementary)
- Gentle aeration (fine bubbles)
Culture Procedure:
- Add the entire starter culture to 10 L of seawater
- Add a small amount of nannochloropsis daily (maintain a pale green color)
- Within one week, a mixed population of adults, eggs, and nauplii (larvae) forms
- The culture becomes harvestable after two weeks
- Harvest half and add fresh seawater and phytoplankton to continue the culture
Key Points:
- Copepod cultures are slower than rotifers, and culture crashes have larger impacts; always maintain 2–3 backup cultures in parallel
- Tigriopus species are hardy and tolerate higher temperatures (25–30°C) well, making them ideal for beginners
- Tisbe species are smaller, making them better suited for feeding small-mouthed fry
Utilizing Copepod Refugia
By continuously culturing copepods in a sump or dedicated refugium, you create a natural influx of copepods into the main tank. This "copepod self-sufficiency system" is highly effective for long-term maintenance of species requiring live food, such as Mandarin Fish and Red Sea Dragon.
Integrated Management of Culture Systems
Example weekly schedule for stable supply of three live food types:
| Day | Tasks |
|---|
| Monday | Nannochloropsis propagation • Fresh seawater addition |
| Tuesday | Rotifer harvest • Nannochloropsis addition |
| Wednesday | Rotifer harvest • Copepod check |
| Thursday | Nannochloropsis propagation |
| Friday | Rotifer harvest • Copepod half-harvest and propagation |
| Saturday | All culture container cleaning and reset (monthly) |
| Sunday | Record keeping • Starter culture stock inventory check |
Common Breeder Pitfalls:
- No backup when rotifer culture crashes – maintain multiple containers and freeze-preserve starter cultures
- Nannochloropsis depletion causing rotifer starvation – establish stable nannochloropsis before starting rotifers
- Direct sunlight causing copepod culture crashes – enforce indirect lighting and indoor management
Conclusion — Live Food Cultivation is the Core of Marine Fish Breeding Infrastructure
In marine fish breeding, establishing a stable home culture system for live food is a prerequisite for all success. By building a three-stage cultivation pyramid—nannochloropsis → rotifers → copepods—you create a foundation for raising diverse marine fish larvae.
While culture crashes and failures are common initially, sharing cultivation expertise among breeders is equally important. Through the br-choku community, breeders can share starter cultures and exchange breeding knowledge. To promote captive-bred (CB) individuals and advance the marine fish breeding community, we encourage you to take on the challenge of live food cultivation.
