Scientific Classification
Kingdom: Animalia | Phylum: Rotifera | Class: Monogononta | Order: Ploima | Family: Brachionidae | Genus: Brachionus | Species: B. plicatilis (L-type, "large" morphotype)
What Are L-Type Rotifers?
Marine rotifers of the Brachionus plicatilis species complex are the most widely used live first feed in marine fish hatcheries worldwide, and they have become an increasingly popular zooplankton feed for reef aquariums. Hatcheries sort them into two practical morphotypes: the large L-type (Brachionus plicatilis) and the small S-type (Brachionus rotundiformis). PodDrop Marine Rotifers are the L-type: the larger, cooler-water form that suits the broadest range of reef and breeding applications.
L-type rotifers have a lorica (the rigid outer shell) measuring roughly 130–340 µm, averaging about 240 µm, while S-type rotifers measure 100–210 µm with an average near 160 µm. In practical terms, an L-type rotifer sits between live phytoplankton (2–20 µm) and the smallest copepod nauplii (around 50–100 µm) on one side, and adult copepods such as Tisbe biminiensis (500–900 µm) on the other. That gap is exactly why rotifers matter: they are the right prey size for organisms that cannot yet handle copepods, but need something larger and more mobile than algae cells.
Rotifers are soft-bodied, slow-swimming animals with a crown of cilia (the corona) that creates a feeding current and provides gentle propulsion. The slow, steady movement is easy for larval fish and coral polyps to capture, which is one reason rotifers outperform faster-moving prey in the first days of larval life.
L-Type vs S-Type: Choosing the Right Rotifer
- Size: L-type 130–340 µm (average ~240 µm); S-type 100–210 µm (average ~160 µm).
- Temperature: L-type grows best at cooler temperatures, roughly 18–26 °C (64–79 °F); S-type is a warm-water form with an optimum of 28–35 °C.
- Best for: L-type suits most reef tanks, clownfish and dottyback larvae, filter feeders and coral feeding; S-type is reserved for species with very small mouth gapes, such as certain tropical grouper, snapper or angelfish larvae.
- Storage: L-type tolerates refrigeration better, which is why it is the standard for shipped live rotifers and for aquarists who hold a culture or bottle in the fridge between feedings.
For reef aquarists, L-type is almost always the right choice. The slightly larger body carries more nutrition per individual, stays visible to the eye as a fine "dust" in the water column, and remains available to corals for longer before being filtered out.
Environmental Requirements and Tolerance
Salinity: Brachionus plicatilis is remarkably euryhaline, surviving from roughly 1 to 97 ppt, but it reproduces best below 35 ppt. Commercial cultures are typically run at 15–25 ppt; growth slows noticeably above 30 ppt. Rotifers added to a reef tank at 35 ppt remain alive and active for many hours, which is all that matters for feeding, but if you intend to culture them at home, dilute to about 20 ppt (specific gravity ~1.015) for the fastest population growth.
Temperature: L-type cultures do best at 18–26 °C (64–79 °F). Normal reef temperatures of 24–26 °C are fine for feeding and for culture. Above 30 °C the L-type loses ground to bacteria and ciliates and populations crash more easily.
Oxygen and water quality: Rotifers need gentle aeration and are sensitive to ammonia. Overfeeding a culture is the most common cause of a crash: uneaten algae or yeast decays, ammonia rises, and the population collapses within a day or two. Clear, slightly tinted culture water is a good sign; cloudy, foul-smelling water is not.
pH: Cultures are tolerant between about 7.5 and 8.5, so standard seawater pH is suitable.
Life Cycle and Reproduction
Under good conditions rotifers reproduce asexually: amictic females produce diploid eggs that hatch into females without fertilization, carried on the body until hatching. At 20 °C and 20 ppt a well-fed female produces around 20 offspring over a reproductive period of about a week, and lives roughly 10 days. Because a rotifer can begin reproducing within 1–2 days of hatching, a healthy culture can double in under a day and routinely reaches several hundred individuals per millilitre.
When conditions deteriorate (crowding, starvation, temperature stress), cultures switch to sexual reproduction: mictic females produce males and fertilized resting eggs (cysts) that sink and survive until conditions improve. Seeing many egg-free females, males or resting eggs is an early warning that a culture needs to be split, fed better, or restarted.
Counting rotifers is simple: swirl the culture, draw 1 mL with a pipette onto a slide or into a small dish, add a drop of freshwater or Lugol's to slow them, and count under low magnification. A feeding-grade bottle or a culture ready to harvest will typically carry 200–500 rotifers per millilitre; densities above about 1,000 per mL are unstable without continuous feeding and filtration.
Nutrition, Gut Loading and Enrichment
Rotifers are non-selective filter feeders that ingest particles of roughly 1.5–20 µm: microalgae, yeast, bacteria and fine particulates. Their nutritional value to your fish or corals is almost entirely a function of what they ate in the last few hours. A rotifer is, in effect, a swimming delivery capsule for whatever was in its gut when it was consumed.
That is why rotifers are always paired with live phytoplankton. Nannochloropsis is the classic rotifer culture food: it is the right particle size, it is rich in EPA, and it holds up in the culture water. For higher DHA, add Isochrysis or Tisochrysis lutea for the final 4–12 hours before feeding out. Tetraselmis adds bulk and vitamins. A mixed diet consistently produces larger, more fecund rotifers than any single species.
Practical rule: feed little and often. Rotifers clear their gut in well under an hour, so a bottle fed in the morning and dosed into the tank in the evening has already lost most of its value unless phytoplankton is added to the bottle before feeding. Shake a small volume of live phyto into the rotifer bottle 30–60 minutes before dosing and you deliver both the rotifer and a fresh algal gut load to the tank.
Reef Aquarium Applications
Coral and filter-feeder nutrition. Rotifers are an excellent zooplankton food for LPS and many SPS corals, zoanthids, gorgonians, non-photosynthetic (NPS) corals, feather dusters, clams and sponges. Their 200–300 µm size matches the prey capture range of a wide range of polyps, and because they swim slowly in the water column they stay available longer than frozen foods that settle. Dose after lights-out when polyps are extended, with pumps briefly reduced, and target-feed NPS corals directly with a pipette.
Breeding marine fish. Rotifers are the standard first feed for clownfish, dottybacks, gobies, blennies, cardinalfish (as a supplement) and many other captive-bred species. Larvae are offered rotifers at 5–15 per mL from first feeding, typically the first 5–10 days, before transitioning to copepod nauplii or Artemia. Enrichment with DHA-rich phytoplankton in the hours before feeding is critical for survival through metamorphosis.
Seeding and feeding copepod populations. Rotifers are not a copepod substitute, but they complement a copepod program. Rotifers feed the smallest mouths in the system now; live copepods establish a self-sustaining population that feeds mandarins, wrasses and pipefish over months. Many hobbyists dose rotifers weekly while their copepod population builds.
Refugium and microfauna support. Rotifers that are not eaten contribute to the microfauna food web, feeding sponges, tunicates and benthic filter feeders in rock and sand.
Culture Methods and Production
Rotifers are one of the easiest live feeds to culture at home, provided you keep the culture fed and clean.
- Vessel: a 2–5 gallon bucket or a 1-gallon jug with a rigid airline producing a slow stream of bubbles (no airstone; fine bubbles trap rotifers in foam).
- Water: new saltwater mixed to 18–22 ppt, 22–26 °C, kept out of direct sun.
- Starter density: 20–50 rotifers per mL. Acclimate chilled rotifers to culture temperature over 30 minutes.
- Feeding: add enough live phytoplankton to tint the water light green, two or three times a day. When the water clears, feed again. Avoid turning the culture dark green; excess algae decays overnight.
- Harvest: once the culture reaches 300–500 per mL (usually 4–7 days), harvest 20–30 percent daily through a 50–60 µm sieve, rinse gently with tank water, and feed out. Replace the harvested volume with fresh water and phyto.
- Reset: restart from a fresh portion every 2–4 weeks, before detritus builds up, and keep a small backup culture in a second vessel.
Yeast can be used as an emergency food, but it fouls water quickly and produces nutritionally poor rotifers. Live phytoplankton remains the gold standard for both culture stability and feeding value.
Receiving and Storing Live Rotifers
PodDrop live rotifers are packed with live phytoplankton and shipped Monday–Wednesday by insulated 2-day service like our other live cultures. On arrival, open the package promptly and inspect the bottle under a light: you should see a fine, slowly swirling haze of individuals. Store the bottle in the refrigerator door (4–8 °C), loosely capped, and gently invert it once a day; cold slows metabolism so the population holds for 1–2 weeks. Dose a portion directly into the tank, or use the bottle to start a culture. Full handling guidance is in Receiving Your Live Cultures.
Advantages and Considerations
Advantages:
- Right size for small mouths: 130–340 µm fills the gap between phytoplankton and copepods.
- Fastest-reproducing live feed: populations can double daily and reach hundreds per mL.
- Slow, visible swimmers: easily captured by larval fish and coral polyps.
- Flexible nutrition: gut-load with any PodDrop phytoplankton to tailor EPA/DHA.
- Easy to culture: bucket, airline and live phyto are all you need.
- Cold-tolerant L-type: stores well in the refrigerator and ships reliably.
Considerations:
- Not self-sustaining in a reef tank: unlike copepods, rotifers are filtered or eaten out within a day or two and must be re-dosed.
- Nutritional value depends on gut content: unfed rotifers are mostly water; always pair with phytoplankton.
- Cultures crash if overfed or overheated: keep water lightly tinted and below 28 °C.
- Too small for adult mandarins and wrasses: choose copepods for those fish.
Frequently Asked Questions
Are rotifers reef safe?
Yes. Rotifers are a natural component of marine zooplankton. They do not harm corals, invertebrates or fish, and any that are not eaten are removed by filtration or consumed by microfauna.
How many rotifers should I feed a reef tank?
A common starting point is 10–20 mL of a dense bottle (200–500 rotifers per mL) per 25 gallons, two or three times a week, with pumps reduced for 15–30 minutes. Increase for NPS-heavy systems, decrease if nutrients climb.
Can I feed rotifers without phytoplankton?
You can, but their value drops sharply within an hour of their last meal. Adding a splash of live phyto to the bottle before dosing is the single biggest improvement you can make.
What is the difference between rotifers and copepods?
Rotifers are smaller, softer, reproduce faster and must be re-dosed; copepods are larger, more nutritious per individual, and establish a self-sustaining population in rock and sand. Breeding programs typically start larvae on rotifers and transition to copepod nauplii.
How long do live rotifers last in the fridge?
Kept cold (4–8 °C) with a little phytoplankton and inverted daily, a bottle remains usable for about 1–2 weeks. Use the freshest portion for larval fish.
Sources and Further Reading
- FAO Fisheries Technical Paper 361, Manual on the production and use of live food for aquaculture: Rotifer strain differences (L-type vs S-type) and general culture conditions.
- Ghent University, Aquaculture course material: Rotifers as live feed.
- Reed Mariculture: Reliable Rotifers.
- Korstad et al., Life history characteristics of Brachionus plicatilis fed different algae: Springer.
- Lawrence et al., The complete and updated Rotifer Polyculture Method: PMC.
- Determination of the optimal conditions for mass culture of large-type rotifers at low temperatures: Water (MDPI).