Seed Shrimp Profile: Ostracods in Shrimp and Fish Tank

Seed Shrimp Profile Ostracods in Shrimp and Fish Tank

Ostracods, commonly referred to as Seed shrimp, are microcrustaceans that can be found almost in any shrimp or fish tank.

For a variety of fish species, Seed shrimp offer a good source of food, whereas in shrimp tanks will be an additional clean-up crew. Even though there is also an opinion that ostracods can be dangerous for aquarium pets, this is not entirely true.

In this article, I will try to examine the profile of ostracods, including their life cycle, diet, reproduction, and more.

What are Ostracods?

Ostracods are a group of small bivalved crustaceans with up to 8 pairs of limbs in adults, plus copulatory limbs and a bivalved carapace with no growth lines. 

These crustaceans initially appeared during the Ordovician period, which began roughly 485 million years ago, according to fossil records.

Since their appearance on Earth, ostracods have spread all over the world and can be found in almost any aquatic environment, whether it be marine, brackish, or freshwater. Depending on the species, these tiny crustaceans can survive on low and high temperatures, low oxygen, or even anoxic conditions, and tolerate a wide range of pH from 4.6 to 13. Basically, these creatures can easily survive anywhere (from the oceanic abyss to temporary inland water bodies or even semi-terrestrial habitats), which is a testament to their exceptional ability to adapt and thrive.

Why are They Called Ostracods or Seed Shrimp?

The word ‘Ostracod’ comes from the Greek word ‘Ostrakon’, which means ‘shell’.

They are also called ‘Seed shrimp’ because of their tiny size and shrimp-like appearance. The word ‘shrimp’ in this case refers to their general shape and movement, rather than their taxonomic classification as true shrimp.

Description of Ostracods

Seed Shrimp Profile Ostracods in Shrimp and Fish Tank main
photo credit to Petrovich

Ostracods have a quite unique and interesting appearance, and their small size and transparency make them a popular choice for microscopic observation and study.

Size. Ostracods are small, aquatic crustaceans that typically measure between 0.2 and 2.0 millimeters in length, depending on the species.

Carapace. They have a hard, calcified carapace with two valves enclosing completely the soft body to protect their entire body, giving them a distinctive appearance. Depending on the species, the carapace is usually oval or elongated in shape and can be transparent, translucent, or opaque.

They represent an efficient hydrodynamic shape, which helps to overcome the resistance of the surrounding water.

Appendages. There are 7 pairs of modified appendages. The first four pairs are cephalic appendages.

These crustaceans have two pairs of antennae, with the first pair being longer and more prominent than the second. They also have two pairs of appendages, which are used for swimming and other movements, and three pairs of thoracic legs. The abdomen is usually small and tucked underneath the body, with the tail fan being reduced or absent.

Body. There is no true segmentation of the body. In some species, there can be seen a faint constriction in the middle divides the body into cephalic and thoracic regions. The rudimentary abdomen is fused with the thorax.

The digestive tract is well differentiated with an atrium, mouth, oesophagus, stomach, intestine, hindgut, and anus.

Movement. Ostracods move by using their multiple pairs of legs, which are located on their thorax. They use a rhythmic motion to paddle through the water, allowing them to move in a relatively quick and agile manner. Additionally, some ostracods have modified appendages called antennae, which they can use to crawl or cling to surfaces.

Ostracods are important members of aquatic ecosystems, serving as prey for fish and other aquatic organisms, and contributing to nutrient cycling and sediment formation.

What Species Do I have in the Tank?

To date, there are over 30,000 known species of ostracods, and new species are still being discovered. Therefore, I am pretty much sure that it is not possible for  ordinary aquarists to find out the exact species they may have in their tank.

For example, according to the study, there are close to 2,000 species and about 200 genera of Recent freshwater Ostracoda. Such families as Cyprididae (1,000 spp.) and Candonidae (c. 550 spp.) represent more than 75% of the extant specific diversity; the remaining 11 families comprise the other 25% of the freshwater species.

How do we Get Ostracods in our Tanks?

Ostracods are adept hitchhikers. We can literally get them out of nothing and accidentally introduce them into the tank.

We can easily get them from plants, rocks, and driftwood, especially if they were collected from the wild. In some cases, freshwater limpets may come even with new livestock (on other snail shells) or in the water bag from a seller.

Therefore, if you do not want them in your tank it is essential to disinfect and/or quarantine everything before putting it in the tank.

Warning: However, even by doing so, you cannot be absolutely sure that Ostracods will not get into the tank anyway. They are extremely hardy and true survivors.

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Are Ostracods Harmful to Plants, Dwarf Shrimp, and Fish?

Seed Shrimp Profile Ostracods in Shrimp and Fish Tank manyNo, they are not. Freshwater ostracods are considered harmless to plants, dwarf shrimp, and fish. On the contrary, they can even be beneficial to our tanks.

In shrimp tanks, ostracods will function as natural cleaners by feeding on excess food and decomposing material. Even though some seed shrimp will compete with dwarf shrimp for food, in the long run, dwarf shrimp will be the winners. Of course, they will not disappear but there will be way fewer of them.

In fish tanks, ostracods will serve as a natural food source for fry and even some adult fish. In contrast to a shrimp aquarium, where ostracods can swim freely throughout the water column, in a fish aquarium they tend to stay closer to the substrate and seek shelter within it.

On the Internet you may find that ostracods can be divided into 3 main categories:

  • herbivores,
  • omnivores,
  • carnivores.

As a result, people immediately assume the worse and start panicking when they see these creatures in their tanks.

Well, their fears are greatly exaggerated!

There are very few carnivorous species of copepods, and they usually inhabit the deep sea. Those species are known to prey on other ostracods, larvae, rotifers, and other small organisms. Most ostracods species are omnivores.

What do Ostracods eat in our Tanks?

As I have already mentioned, ostracods are generally scavengers and will feed on detritus and organic debris in the substrate and water column.

In our tanks, they will also consume leftovers, algae, biofilm, and other microscopic organisms present in the tank.

An explosive growth of ostracods in an aquarium usually indicates overfeeding, and this overfeeding is often very excessive!

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Life Cycle of Ostracods

The life cycle of ostracods typically consists of 3 main stages: the egg stage, several juvenile instars separated by molts, and an adult instar following the terminal molt. 

Depending on the species, ostracods can reproduce sexually or even asexually (this is called parthenogenesis). Current data shows that freshwater ostracods most commonly reproduce asexually, for example, no male has been recorded in 57% of 286 species of Cypridoidea, or in 28% of 50 species of Cytheroidea in Europe.

  1. Egg stage: The ostracod female lays eggs. The eggs are typically carried by the female until they hatch. The duration of the egg stage depends on environmental conditions and varies widely among species but can last anywhere from a few days to several months.
  2. Nauplius stage: The hatched ostracod larvae emerge as nauplii, which are small, planktonic larvae. The nauplii molt several times and develop into adults. The stage usually lasts for a few days to a few weeks.
  3. Adult stage: The juveniles continue to grow and molt until they reach adulthood. Adult ostracods can reproduce and produce eggs, continuing the life cycle.

The adult stage can last for several weeks to several months, depending on the species and environmental conditions.

As ostracods age, they become less active and eventually die. The shells of dead ostracods may accumulate in the substrate of the culture and contribute to the overall organic matter content.

Is It Worth Culturing Ostracods as Live Food for Fish?

In fact, I would not say that culturing ostracods as live food for your fry or fish would make economic sense.

Unlike other live foods (such as Brine Shrimp, Daphnia, Grindal Worms, Bloodworms, Blackworms, etc.) ostracods do not reproduce quickly enough to sustain a constant supply. Additionally, their hard shell slows down the fish’s ability to access the nutrients they contain, resulting in delayed satiation.

Another drawback is that ostracods are very small and of little interest to adult fish, serving merely as a small snack.

Therefore, while ostracods may be a nutritious food source, their small size and slow reproduction rate may make them less practical as a primary food source for fish.

Under optimal conditions, the population of seed shrimp in the tank doubles every 4-6 weeks. It is worth noting that ostracods can reproduce at a very young age, and their life cycle can overlap with multiple generations present in culture at the same time.

How to Culturing Ostracods

Nonetheless, if you have still decided to try breeding ostracods, it can be easily done.

To culture ostracods in home conditions, you will need the following materials:

  1. Any container: The size of the container will depend on how much live food you want to culture and the space you have available. You can breed them even in a small plastic bottle.
  2. Water: You will need freshwater to fill the container. You can use tap water that has been treated to remove chlorine and other chemicals, or you can use old aquarium water. Actually, old aquarium water will be even better because it is already contain some food for them.
  3. Substrate: No need.
  4. Lighting: You can put the container into direct sunlight to boost algae growth.
  5. Food: Ostracods can feed on a variety of organic matter, including algae, yeast, and decaying plant matter. You can use commercial fish food, spirulina powder, or crushed fish flakes as a source of food for the ostracods.
  6. Air pump: No need.

Here’s a step-by-step process for culturing ostracods in home conditions:

  1. Add water. The water should be at room temperature.
  2. Add food. Add a small amount of fish food, spirulina powder, or crushed fish flakes to the water to provide a food source for the ostracods. You can also add a small amount of decaying plant matter or algae to the water.
  3. Introduce the ostracods.
  4. Done.

Where can I get Ostracods?

Ostracods can be found in various aquatic environments, such as ponds, rivers, lakes, and even puddles. They may also be present in aquariums or can be purchased from some online aquarium stores.

How to Remove Ostracods from Aquariums?

It can be really hard to remove them completely once they get into the tank. However, there are some ways to control their population.

  1. Reduce feeding. Ostracods thrive in environments with abundant food. By reducing the amount of food you are giving your aquatic pet, you will significantly reduce the population of ostracods.
  2. Siphon the substrate. Ostracods prefer to stay near the substrate where they can hide. Thus, use a siphon to suck out the ostracods from the substrate of the tank. This method may require some patience and precision.
  3. Introduce natural predators: Ostracods are eaten by fry and small fish species (such as  Neon Tetras, Danio rerioEndlersLeast Killifish, etc.). Even though this method does not guarantee complete eradication, at least you will not see them in the water column anymore. 

In Conclusion

Ostracods are fascinating little creatures with a long evolutionary history, and they continue to play an important role in aquatic ecosystems today.

Freshwater ostracods are not a foe to aquarium setups. Through their daily activities, these tiny crustaceans contribute positively to the tank’s cleanliness and that’s commendable. In addition, they are a food source for fish.

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  1. Ruiz, F., M. Abad, A. M. Bodergat, P. Carbonel, J. Rodríguez-Lázaro, M. L. González-Regalado, A. Toscano, E. X. García, and J. Prenda. “Freshwater ostracods as environmental tracers.” International Journal of Environmental Science and Technology10 (2013): 1115-1128.
  2. Boomer, Ian, David J. Horne, and Ian J. Slipper. “The use of ostracods in palaeoenvironmental studies, or what can you do with an ostracod shell?.” The Paleontological Society Papers9 (2003): 153-180.
  3. Williams, Mark, David J. Siveter, María José Salas, Jean Vannier, Leonid E. Popov, and Mansoureh Ghobadi Pour. “The earliest ostracods: the geological evidence.” Senckenbergiana lethaea88 (2008): 11-21.
  4. Rodriguez-Lazaro, Julio, and Francisco Ruiz-Muñoz. “A general introduction to ostracods: morphology, distribution, fossil record and applications.” In Developments in Quaternary Sciences, vol. 17, pp. 1-14. Elsevier, 2012.
  5. Butlin, Roger, Isa Schön, and Koen Martens. “Asexual reproduction in nonmarine ostracods.” Heredity81, no. 5 (1998): 473-480.
  6. Martens, Koen, Isa Schön, Claude Meisch, and David J. Horne. “Global diversity of ostracods (Ostracoda, Crustacea) in freshwater.” Hydrobiologia595 (2008): 185-193.
  7. Victor, Reginald, and C. H. Fernando. “The freshwater ostracods (Crustacea: Ostracoda) of India.” Records of the zoological survey of India74, no. 2 (1979): 147-242.

4 thoughts on “Seed Shrimp Profile: Ostracods in Shrimp and Fish Tank

  1. Hi Michael,
    I was out of fishkeeping for decades, but I’m retired now and have 1 ten gallon tank with Neocaridina. I’m pretty sure that my ostracods came in when I got my shrimp at the end of April 2023. I’m doing quite well with my shrimp, starting with 13 at the end of April, I got up to over 120 within a couple of months. I would be happy to maintain that level.

    I keep the ostracods pretty much under control. I don’t really like to see them in the water column, but I know they mean my tank environment is generally healthy. I mainly see them on the front of the glass and siphon them from there to keep the numbers down.

    I do like to feed GlasGarden powdered foods, including Bacter AE, Shrimp Baby and Shrimp Fit and it’s hard to not overfeed those foods, so I measure it carefully and I use the apparent population levels of ostracods to help indicate when I’m feeding a little too much/too often. I do also feed other foods in rotation.

    I have heard that ostracods can out-compete newborn shrimp and I wanted to check with you. If I do my best not to over feed, and keep the observable ostracods down to just some on the glass, should I be in good shape to insure that most of the food goes to shrimplets and not seed shrimp?

    Thank you very much for your opinion.

    1. Hi Thomas H Saunders,
      You raise a good point. Ostracods may sometimes compete with baby shrimp for food resources in a tank, especially if they are present in large numbers.
      Nonetheless, this is not your case. Using powdered supplements ensures shrimplets get adequate nutrition to grow anyway.
      There are a few things you can do to minimize this competition even more:
      – You can also crush up shrimp pellets or flakes into small pieces. Ostracods cannot consume large pieces.
      – Provideg ample grazing surfaces like plants, driftwood, rocks, leaves (to grow biofilm), it ill give baby shrimp more places to find microscopic food.
      As long as you control ostracod populations, they should not cause any problems even for your shrimplets.
      Best regards,

  2. Thanks Michael, I appreciate your reply. I think the tank is in pretty good shape. I have a nice growth of green dust algae on the back and sides of the tank. I have a good sized Java fern and a patch of floating water sprite that is usually full of shrimp. And a tree-shaped piece of Spiderwood.

    I like to feed a tiny amount every day, And I do remove any left overs, if there are any after 3 hours or so. Usually, all the food is gone within 1 to 2 hours. I know you recommend feeding less often.

    I just wanted to be sure that I’m on track, and I do think I am.

    Thanks again.


    1. Hi Tom,
      It seems that your aquarium is in good hand. When it comes to feeding, the question is not how often but how it affects the aquarium’s condition.
      You clean it every day after feeding, and I must say, that’s excellent! Seriously. The majority, no, the absolute majority of people either never do this or do it extremely rarely, despite it being a common recommendation for aquarium care. In this case, you can feed your shrimp frequently.
      Best regards,

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