Freshwater Isopod Care Sheet (Asellus Aquaticus)

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Isopods are an order of crustaceans whose members may live on water as well as land. Freshwater isopods are somewhat similar to shrimp, although their latin name Asellus literally means “donkey”. In English, they are sometimes referred to as Water Louse, Aquatic Pillbugs or Sowbugs. Their terrestrial cousins are also informally known as “roly poly” and more commonly kept as pets. But the freshwater variety is becoming more and more popular in the aquarium trade – asellus aquaticus care is fairly easy and can be quite rewarding.

Asellus Aquaticus Care Sheet

Size:0.3-0.5 inches (8-15mm)
Color:White, Brown, Black, Yellow, or Grey
Behavior: They tend to keep to themselves, floating around eating all day.
Aquarium:5+ gallons (15+ liters)
can live in smaller planted ecosystem
do not require cycled tank
Water:pH of 6.0-7.2, can live in “dirty” hard water (aged tap water is fine)
Temperature: 65-75°F (18-23°C)
do not breed in coldwater
Lifespan:8 to 20 months

Natural Habitat

In nature, aquatic sowbugs populate streams, ditches and various types of water. In general, they are typical of tinned or lentic environments of North America, Europe and Russia. This animal is only rarely found in streams with stronger currents, and if so usually nearby water banks where the risk of being swept away by the current is lower. As a matter of fact, compared to shrimp and other crustaeans, these creatures are by far not skilled swimmers, which is why they instead tend to keep to the surface of the water. They are discreet in their movements, using their large number of legs to run along water currents, scouting through thick vegetation in order to seek both shelter and nourishment. Asellus aquaticus feed on decomposing material, because of these, they can thrive in polluted and “dirty” waters.

Main characteristics and features

In the wild, asellus aquaticus have a coloration normally ranging from light gray to brownish, with a scattered white spot pattern throughout their body. Through selective breeding, some keepers have managed to get their hands on yellow and black specimens, which are still relatively rare in the trade. Female isopods are sized between 0.3 and 0.5 inches (8-15mm), whereas males are slightly bigger in size, growing up to 0.7 inches (about 20mm). Asellus aquaticus can be easily recognized by their flat body and seven pairs of leg.

Life cycle and reproduction

Freshwater isopod live on average between 9 and 20 months, during which they undergo four stages of development. Water conditions and temperature can affect both the growth rate and life span of these creatures. Asellus aquaticus that live in cold water will grow more slowly and live longer, whereas those that live in warmer environments will grow larger but live shorter lives. In nature, asellus aquaticus reproduces seasonally in the summer, but in captivity it will reproduce constantly as long as water temperature is warm enough.

Diet and nutrition

Asellus aquaticus are bottom dwelling scavengers that mainly feed on dead plant and animal matter (i.e. microorganisms such as fungi and bacteria that they find on plant leaves). In a tank, they are particularly helpful in getting rid of nasty algae and food leftovers from other fish that would otherwise end up polluting the water. This is just one of many reasons to add asellus aquaticus to your freshwater tank.

Tank requirements and water parameters

Compared to other crustaceans, asellus aquaticus care is a no-brainer, as these creatures are extremely low maintainance. This thanks to their diet based on detritrus and to their ability to withstand most water conditions – they can tolerate a slightly acidic pH and higher TDS levels, as they will feed on virtually any kind of organic material floating around. You can keep them in a non-ventilated tank or even in a medium-sized bowl (e.g. a jarrarium) without the need to replace water – just top it up with new water every two weeks or so to make sure the container doesn’t drain out. Aged tap water is perfectly fine to use with these creatures. Compared to shrimp, isopods are also much better suited for a self-sustained planted aquarium setup, and you can use smaller containers of less than 5 gallons without any major issues.

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Asellus Aquaticus FAQ

asellus aquaticus / freshwater isopods

What is the difference between asellus aquaticus, freshwater isopods, and water louse?

None. Asellus aquaticus is the scientific name of a type of isopod that lives in freshwater, and which is more commonly known as water louse in certain countries like the UK. This creature also goes by the informal name of aquatic pill bug or aquatic sowbug.

What size should an aquarium tank for asellus aquaticus be?

Asellus aquaticus can live in very small tanks. A nano planted environment of as little as 1 gallon capacity can be sufficient, although larger tanks will require less maintainance.

Will asellus aquaticus escape from its tank?

No. Asellus aquaticus are fully aquatic and are not capable of climbing, which is why open containers and rimless aquarium can be used without worries.

What food should I give to asellus aquaticus?

Asellus aquaticus are natural scavengers will naturally munch on any decaying plant, algae, and decomposing animal matter in your tank. You can additionally feed them dry plant leaves.

Do asellus aquaticus prey on shrimplets and fish fry?

No. Asellus aquaticus are scavengers by nature and will only feed on other animals if they are already dead.

Can you breed asellus aquaticus in captivity?

Yes. Freshwater isopods are fairly easy to breed in an aquarium tank. They reproduce seasonally in nature, you can stimulate mating by increasing water temperature to simulate environmental conditions n the summer.

Where can I find asellus aquaticus in the wild?

Different species of asellus aquaticus can be found in different parts of the world, but getting your hands on some should be fairly easy no matter where you are located. Cultures can be found nearby the surface of water streams like rivers and ponds. It is not uncommon for people to pick up wild plants for their tanks and then discover they introduced freshwater isopods by accident.

Where can I buy asellus aquaticus?

There are still not many pet stores or other commercial retailers selling freshwater isopods, although you can sometimes find them sold as live pet food or lab specimens. In some countries, individual breeders have started trading asellus aquaticus through online platforms and social media, and you can sometimes even find them for sale on amazon. We maintain a regularly updated list of online asellus aquaticus traders worldwide.

How long does asellus aquaticus live?

Under the right conditions, freshwater isopods can live for up to 2 years. Higher levels of water pollution and water temperature will shorten this life span, although warmer climates will speed up growing and reproduction rate.

Is asellus aquaticus good as a tank cleaner?

Yes – asellus aquaticus will feed on about any type of detitrus that may form in your tank, as well as keeping vegetation from growing too much. They will eat brown and green algae.

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7 thoughts on “Freshwater Isopod Care Sheet (Asellus Aquaticus)”

  1. This article has been extremely helpful to me, but it left me with a couple of questions. How many isopods should I have per gallon? (I have a 2.5 gal tank that I might put live plants in) and do they reproduce asexually?

    1. Hi Grace,

      asellus aquaticus reproduce sexually (the male attaches to the female in a rather theatrical way) and for such a small tank I would start with a small culture of 10-15 isopods.


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