Rotifers are one of the most popular types of live food for aquarium fish fry. This food has gained popularity due to its nutritional value and ease of culturing.
Cultivating marine or freshwater rotifers is a pretty simple process that doesn’t require almost any materials. Of course, you can buy special kits for cultivating rotifers, or you can do it yourself (DIY) as it mostly requires a small container, a culture, a fine-mesh net, and some food for them.
In this article, I will describe what Rotifer is, its life cycle, and reproduction. I will also explain the purpose and benefits of harvesting Rotifers, different methods to do it, and what to avoid when cultivating them.
Rotifers as Live Food
Due to the fact that many commercial fish fry productions effectively utilize rotifers as live food, you can find information online suggesting that this is due to the high nutritional value of this culture.
While this holds some truth, it’s not entirely accurate.
The truth is that rotifers themselves do not possess significant nutritional value. Instead, the contents of their stomachs and their eggs are the crucial components that contribute to their nutritional value.
Furthermore, the rotifer’s nutritional qualities can be artificially manipulated to enhance its suitability as a food source.
According to the study, unenriched rotifers only contain:
- protein 41 – 45%
- lipid levels 7–8%
- fatty acid composition 9 – 14%
- The Ca levels in rotifers are the same or even higher than in copepods.
The rotifer Brachionus plicatilis is indispensable for aquaculture. They play a crucial role in aquaculture by serving as a primary food source for the early stages of development in various species of finfish and crustaceans.
- This tiny organism is ideal as an initial food due to its optimal size range of 130-320 μm,
- They thrive in a planktonic environment,
- They can live in high-density cultures,
- Rotifers have a rapid reproduction rate.
All these features make it well-suited for mass production under controlled conditions. Furthermore, the rotifer’s nutritional qualities can be artificially manipulated to enhance its suitability as a food source.
For some fish species, especially those with very small fry, rotifers are the only food available for the fry during the first two to three weeks of their life. Thus, culturing them is the key to success in breeding both marine (such as Clownfish) and freshwater fish (for example Neon Tetras, Danio Rerio, etc.).
What are Rotifers?
Rotifers are small, multicellular organisms. They belong to the phylum Rotifera and are found in freshwater, brackish, marine, and even terrestrial environments.
Rotifers play a vital role in aquatic ecosystems as primary consumers. They feed on algae, bacteria, and detritus. In this way, they help recycle nutrients and helping to maintain the overall balance of the ecosystem.
Currently, there were over 2,200 described species of rotifers.
Etymology of Rotifers?
The scientific name “Rotifer” originated from two Latin words: “Rota” meaning wheel and “Fer” meaning to bear or carry. Literally translated, it means “wheels carrying” due to the corona around the mouth
The rotating apparatus of rotifers (corona) is located in the front end and consists of small hair-like structures, which beat and create a flow that drives water and small particles such as bacteria, algae, and other similar substances into the mouth.
Description of Rotifers
Initially, rotifers were classified as roundworms, but now they are considered a separate type of animal.
Size. Rotifers are one of the smallest multicellular organisms. Their length is measured in tenths or even hundredths of a millimeter. The smallest nematode measures about 40 micrometers. The largest species is Ptygura pilula, sometimes referred to as “Giant rotifer.” This species can reach sizes of up to 0.08 inches (2 mm) in length.
Structure. The body is divided into three parts: the head, torso, and leg.
Head (corona). The head has a complex structure with a large number of cilia (corona) arranged in several rows. This ciliary apparatus is used for feeding and locomotion. The synchronous movements of the cilia create water currents that capture food particles directing them straight into the mouth. Additionally, the movement of these hair-like structures allows the rotifer to swim forward.
Torso. After swallowing the food, it enters the torso where the internal organs and digestive system consisting of three sections are located. At the end of the torso, there is an excretory opening called a cloaca.
Leg. Directly under the torso is the leg, which is a muscular protrusion of the body that allows the organism to actively move. At the very end of the leg, there are special glands that secrete cementing substances.
Interesting fact:
- Rotifers have a very consistent cellular composition. It means that each species has a strictly defined number of cells in its body, which does not change throughout its entire life. Growth only occurs through an increase in the size of cells.
Lifespan of Rotifers
Their lifespan can vary depending on the species and environmental conditions. Generally, rotifers have short lifespans ranging from a few days to a few months. Some species, like the Brachionus plicatilis, have a lifespan of around 2-3 weeks.
Interesting fact: Some species are capable of entering a state of cryptobiosis, during which their metabolic processes practically stop. In 2021, Russian scientists were able to revive rotifers that had been in a state of cryptobiosis for over 24,000 years in permafrost samples.
Behavior of Rotifers
Rotifers are primarily free-moving animals, although some species live attached to one spot. Occasionally, parasites or commensals – those that can coexist with other species of living organisms – are also found.
Rotifers Life Cycle
Their life cycle typically involves 3 stages:
- Egg: The life cycle begins with the development of an egg.
- Juvenile: The juvenile rotifer undergoes growth and development, gradually shedding its protective covering as it matures.
- Adult: The mature rotifer. At this stage, the rotifer is capable of feeding, reproducing, and continuing its life cycle.
Reproduction of Rotifers
Rotifers may reproduce both sexually and asexually. It is quite amazing that the specific method of reproduction can vary between species and can even change in response to environmental conditions.
- Parthenogenesis (asexual reproduction). This is the most common form of reproduction in rotifers. Basically, females produce offspring without fertilization by males. The unfertilized eggs develop into embryos, and these embryos hatch into new individuals.
This process allows for rapid population growth under favorable conditions.
Additionally, some rotifer species are capable of producing two types of eggs:
- summer eggs (hatch almost immediately)
- winter eggs (that can survive unfavorable conditions and hatch when conditions improve).
- Sexual reproduction. Fertilization occurs internally, and the females produce fertilized eggs that develop into resting eggs. These resting eggs have a protective outer coating and can survive harsh conditions until they hatch when environmental conditions become more suitable.
In all cases, the newborn rotifers differ from their parents only in body size.
For example, females of Brachionus plicatilis (this species is very popular in aquaculture as a live food source for fish) can produce from several dozen to over a hundred eggs in a single reproductive event.
Interesting fact: In laboratory studies, the eggs of rotifers have been found to retain viability even after several years of freeze-drying at minus 270 degrees Celsius for 4 hours and heating at plus 100 degrees Celsius for 5 minutes.
Diet of Rotifers
Rotifers are primarily filter feeders, meaning they consume tiny particles suspended in the water. They use ciliated structures (hair-like pieces) to funnel water into their mouth.
Generally, they will eat algae (like phytoplankton), bacteria, detritus, decaying organic materials, and even other smaller microorganisms.
DIY Set-Up for Saltwater Rotifers Culture
While it’s certainly possible to purchase pre-made systems for cultivating rotifers, it’s also entirely feasible to set up the cultivation process yourself, as it’s a fairly straightforward system.
Materials Needed:
- Starter culture: Rotifers
- Culture container: small tank or plastic container/bucket/bottle (1-2 gallons or 4-8 liters will be more than enough for ordinary hobbyists)
- Oxygen: air pump and Flexible airline tubing
- Non-Iodized Salt: Aquarium salt, Epsom salt, or Instant Ocean Sea Salt, etc.
- Food: RGComplete, RotiGrow Plus, Instant Algae, NannoPrime, Nannochloropsis, live Phytoplankton, etc.
- Harvesting: 53-micron sieve
- Cleaning: 120-micron sieve
- Test kits: Water quality testing kits (optional but recommended)
Step-by-Step Process:
- Prepare the container. It should be clean, and free of contaminants.
- Prepare water. Fill the container with either seawater (for marine rotifers) or dechlorinated freshwater (for freshwater rotifers).
Note: Do not use old water from your tank. - Acclimation. Put the bag of rotifers in the bucket of water and give it time to temperature acclimate.
- Aeration. Set up an air pump to provide gentle aeration. This helps keep the water oxygenated and the rotifers suspended.
- Add food. The water will turn green.
- Add the culture: Introduce a rotifer starter culture.
- Provide food every day: Rotifers need a consistent food source. You can provide algae or commercial rotifer feed.
Requirements:
- Optimal temperature: 68 – 77°F (20 – 25°С)
- Aeration: 2-3 bubbles per second
- Salinity: 015-1.020 (20-25 ppt)
- Lighting: ambient light
Maintenance of Rotifers Culture
- Use a 120-micron sieve to strain out the larger particles.
- Do 20-30 % water change every day.
- Remove biofilm (surface scum), you can use a paper towel for that.
- Maintain suitable conditions (temperature, salinity (for marine species), and pH) to ensure the well-being of the rotifers. Abrupt salinity change will cause a significant decline.
- Clean the container every day. During cleaning, avoid using items from other aquariums. You might introduce contamination to the culture.
| It is highly recommended to maintain at least two containers in the same developmental stage of the culture process. This precaution ensures that if one culture becomes contaminated and fails, you can still use the other container to maintain progress. |
Keep in mind, if you also do other projects, like phytoplankton or copepod cultures, rotifers can inadvertently cross-contaminate your other cultures, even if you are not using the same equipment. Numerous reports have indicated instances of people encountering such problems.
Feeding Rotifers
To culture rotifers, it is important to feed them constantly. They have an extremely fast metabolism. A single rotifer can devour up to 115,000 cells of Nannochloropsis sp. daily. Therefore, for the best growth, it is recommended to feed them at least 2 times a day.
Rotifers feed best on microalgae (such as Nannochloropsis, Tetraselmis, etc.), typically in the 1 to 10-micron range. The lack of food can also be understood even visually.
For instance, when adding RGcomplete, the water will turn green, but within 4-6 hours, you will notice it becoming lighter. This indicates that the rotifers have consumed what was in the container and need more.
Do not allow the rotifer culture to become completely clear. It is better to feed them in smaller amounts but more frequently.
Harvesting Rotifers
Rotifers reproduce very fast. So, even if you have just started the culture, you can begin harvesting it daily starting from the 3rd day.
It’s best to do this at the same time as water changes. The main challenge here is that these are very small organisms, and you’ll need a special net with at least a 53-micron sieve.
- Prepare the second bucket/bottle.
- Turn off the air pump first. In 5- 10 minutes, the detritus will settle, causing the rotifers to rise.
- Do water change. Scoop the rotifers off the top.
- Use the sieve to filter rotifers from old water.
| Pro tip: Whenever you harvest the culture, it is a good practice to create a log of these events along with taking pictures. This will enable you to develop a visual understanding of what constitutes a sufficiently dense culture. This becomes particularly valuable for times when your culture is not thriving as expected. |
DIY Set-Up for Freshwater Rotifers Culture
To cultivate freshwater rotifers (Philodina acuticornis), you will need practically the same setup, with just two exceptions:
- You need freshwater instead of saltwater,
- Use baker yeast and spirulina as their food sources.
Feeding: Yeast is added at a rate of 1-1.5 grams per gallon of water. Then, you can take a spirulina tablet and crush it into powder. This amount will be sufficient for 4 gallons (20 liters). Some aquarium enthusiasts also add a dried banana peel (pumpkin or melon) measuring 1 by 1 inch for enhanced nutritional content.
When adding yeast, it’s recommended to first dissolve it in a glass of water and only then give it to the rotifer culture.
In this case, the water will become cloudy rather than turning green. Nevertheless, the principle remains the same – after 12 hours, you will observe the water regaining its clear color, indicating it is time to feed rotifers again.
FAQ about Rotifers Culture
How often should you restart the rotifers culture?
It is recommended to do this every month. Even if you are constantly cleaning their container, various substances will inevitably accumulate that you won’t be able to remove. Therefore, after restarting the culture, it is also important to thoroughly clean and wash the previous container.
Can I feed saltwater rotifers baker yeast?
Yes, it is also one of the options.
On the downside, the process of selecting suitable yeast is often carried out through trial and error, as certain products may not be suitable. It’s also worth noting that yeast may be nutritionally deficient. Thus, using additional additives is recommended to enhance the reproduction rate and overall quality of rotifers in the culture system.
Can I use common salt instead of specialized marine salts to culture rotifers?
Yes, you can use common salt (table salt: 2 – 3.5 ounces per gallon or 15-25 g/l) to make saltwater for culturing rotifers. Some species are so hardy that will live even there.
Nonetheless, it is important to note that using specialized marine salts will allow you to have precise control of salinity. In addition, in the long run, table salt will not provide the full range of essential minerals and elements that marine salts offer.
Therefore, for better results, it is still recommended to use marine salts.
Does it have a smell? Will my house smell bad because of this culture?
There is absolutely no smell from saltwater culture. It is perfectly fine for an apartment, you do not even need to cover it (people usually cover it to protect from potential contaminations).
Is it possible to skip filtering rotifers and directly add them to the aquarium with water?
I would highly recommend you filter them before adding them to the larval tank. The used water may have elevated nutrient levels. So, it can be risky.
What should I do if I don’t have such a 53-micron sieve?
If you do not have that kind of sieve, you could try using at least a double-layered screen coffee filter (or unbleached filter), as they will most likely pass through a single-layer one.
Which type of culture is better to breed, freshwater or saltwater rotifers?
Based on experience, saltwater rotifers have proven to be more stable, including in terms of survival. There is much less chance that something will go wrong with them.
What level of aeration should the container have? Is aeration essential?
In reality, it is possible to culture rotifers even without aeration and while the results might be slightly less optimal, it might not even be noticeable to you. In terms of aeration strength, it should not be too strong (2-3 bubbles per second), as that could push the rotifers to the surface, and the females might end up losing their eggs.
Why is there foam in my rotifer culture?
This is probably because you overfeed them and have strong aeration with small bubbles. Try to reduce it. Additionally, you can increase the size of the bubble by making an oblique cut on the tube.
Do the Rotifers need light?
Although rotifers do not need it and can survive in the dark, they benefit from having a light source in another way.
Light promotes the growth of algae, which serves as their primary food source. Algae require light for photosynthesis, and as the rotifers feed on the algae, they indirectly benefit from the light as well.
I don’t really have a pressing need for rotifers at the moment, so what should I do with the culture?
This can be considered one of the drawbacks because stopping the process of collecting the culture without negative consequences is not possible.
Rotifer culture requires consistent feeding and harvesting; otherwise, a constantly growing population may crash the system. So, essentially, there are two choices: keep feeding and maintaining the culture (even if you’re just discarding the collected yield) or let go of the culture entirely.
What’s the purpose behind changing 30% of the water every day?
The main objective is to keep the rotifers young. Aging rotifers tend to stop producing eggs, which can gradually reduce the overall culture count. By regularly harvesting 20-30% of the culture, you ensure that the population remains statistically young. Additionally, it helps with ammonia.
In Conclusion
Numerous studies and practical experience have shown that rotifers are an excellent food source for animals with very small fry or those who have a larval stage.
The simplicity of the process and the incredibly fast growth rate allow you to feed your animals daily.
If you get interested in cultivating rotifers, it is advisable to start with a saltwater culture, and within just 3 days, you will have a consistent supply of live food.
| Rotifers as Live food | |
| Pros | Cons |
| Simple and easy to cultivate | Suitable only for small fry and larvae |
| Extremely fast reproduction | Requires constant maintenance |
| Its nutritional value can be artificially enhanced | |
| High digestibility | |
| Stay in in the middle and upper water column | |
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References:
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Did povidone iodine was same as iodinol?