Marimo moss Volcanic Shrimps Aquarium

What are marimo moss balls? 

Marimo moss balls translate to “Seaweed balls” in Japan. They are actually not moss, but algae that grows in a spherical shape.

They are found only in certain parts of the world, namely lakes in Japan, Scotland, Iceland and Estonia.

Marimo moss balls in Lake Akan, Japan

The circular motion of the water currents keep them circular in shape.

What’s their significance?
The balls are gifted for good luck. They are also popular as gifts between lovers and amongst friends and family to signify the tight bond between them. Some Japanese even keep them as heirlooms as they can grow up to 200 years.

What are volcanic shrimps?

Volcanic shrimps are found only in hawaii. They are called “opae ula” in hawaiian, with “opae” meaning shrimp, and “ula” meaning red. 

They are also nicknamed “Supershrimp” because of their hardy nature. In the wild, they can live up to 20 years and remain tiny throughout!

You do not have to feed these shrimps because they feed on microalgae in the tank. And in doing so, they keep the tank clean so you don’t have to clean it often. Frequent water changing, air pumps, filters are also not required.

Opae ula lives in anchialine pools, which has a salinity in between saltwater and freshwater.

Seawater seeped from below the ground and rainwater fell from the sky, resulting in brackish water. They cannot survive in tap water as it contains chlorine.

The symbiotic relationship between marimo moss balls and volcanic shrimps

Marimo moss balls are kept together with volcanic shrimps because they trap light and photosynthesise, giving out oxygen for the volcanic shrimps. They also absorb nitrates.

In return, the volcanic shrimps give out waste materials and carbon dioxide which helps the marimo moss balls to make food.

Although the shrimps do not feed on the algae per se, the moss balls contain micro bacteria film which the shrimps feed on. 


Q1) Where can I place my aquarium?
You may place your aquarium under medium or low light, as too much light will cause algae to grow very fast
Ideal temperature is 20-25 degree celsius

DO NOT place under direct sun or next to the window:

Place under medium light i.e. at least 2-3 metres away from the window, or under low light i.e. on shelves or corners where most light is blocked

Q2) What do I do when water level is low?
Keep lid closed at all times to slow down evaporation. But you can buy brackish water (version for topping up) from our website when the water is less than 60% of the tank and it’s affecting the amount of space the shrimps have for swimming.

Q3) Do I have to feed the shrimps?

Do not drop any fish feed or food inside the water because it will decay and bacteria will grow. The shrimps are happy enough with the microalgae inside the water.

Q4) Do I have to switch on the light?

Do not switch on the light for more than 30mins every day because it might lead to algae growing very quickly.

Q5) Will the shrimps grow larger?
Yes they will. Like most crustaceans, they shed their old shell when they grow bigger. Opae ula moult several times in a year. If you see transparent looking shells in your aquarium, it means your shrimps have grown! They will however still look tiny.

Q6) How do I know the sex of my shrimps, and how to have baby shrimps?
It’s hard to tell the sex of the shrimps due to their tiny size. One way to increase the likelihood of them breeding would be to have more shrimps – at least 5. Then it increases the possibility of there being both males and females in the lot. The shrimps have to feel comfortable in the water, and there has to be hiding places in order for them to breed.

Q7) How often do I have to clean my aquarium?

The shrimps doesn’t mind algae because it’s food for them. But if the algae becomes so much that it affects the aesthetics of the tank, you can choose to clean it. If you wish to slow down the growth of algae, you can place it at a location that’s not too bright.

Q8) How do I clean the aquarium? (Light maintenance)

Conduct light maintenance once you see an algae patch, to prevent it from spreading

Light maintenance removes the algae without a water change. Use paper towel to remove algae from the inner surface of the container. Scrub figurines under tap water before putting them back into the water.

For detailed video instructions, click here.

Q9) How do I clean the aquarium? (Heavy maintenance)


Conduct heavy maintenance once more than 50% of the aquarium is filled with algae

Purchase brackish water from us to conduct a full water change. Scrub the contents clean, reassemble your aquarium, then pour the shrimps back in.

For detailed video instructions, click here.

Q10) What’s the life cycle of opae ula?

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