Asellus Aquaticus - Water Isopod / Louse

Asellus aquaticus (Water Louse) – Nature’s Pond Caretaker

In Japan, the healthiest medaka ponds are not kept clean by removing every fallen leaf or piece of organic matter—they are kept in balance by the countless small creatures that quietly recycle nature back into life. Asellus aquaticus is one of these unsung workers.

This peaceful freshwater crustacean spends its days slowly grazing across the pond floor, feeding on softened leaves, biofilm, algae and uneaten food before they have the chance to decay and affect water quality. Every movement contributes to a healthier, more stable ecosystem, helping beneficial bacteria break down waste naturally.

For outdoor medaka tubs and wildlife-style ponds, Asellus are an excellent addition. They thrive amongst leaf litter, aquatic plants, mosses and wood, where they spend much of their time hidden from view, quietly carrying out their work. As they establish and reproduce, they become part of the natural food chain, with young Asellus providing an occasional source of nutritious live food for medaka without the need for intervention.

Unlike many aquarium “clean-up crews”, Asellus aquaticus are perfectly suited to life outdoors in the UK’s changing seasons. They tolerate cool temperatures exceptionally well and continue working throughout much of the year, making them an ideal companion for outdoor-raised medaka.

Whether you are creating a traditional Japanese-inspired breeding tub or simply want a healthier, more natural pond ecosystem, Asellus help transform waste into life, allowing nature to maintain its own balance.

Why Add Asellus aquaticus?

• Natural recycler of fallen leaves and organic debris.

• Feeds on biofilm, algae and uneaten fish food.

• Helps maintain excellent water quality naturally.

• Encourages a balanced, self-sustaining ecosystem.

• Safe to keep with medaka, shrimp and other peaceful freshwater species.

• Breeds readily in established ponds and planted tubs.

• Juveniles provide a natural live food source for medaka and fry.

• Ideal for outdoor ponds, breeding tubs, shrimp aquariums and nature-style aquascapes.

Care Guide

Temperature: 4–28°C
pH: 6.5–8.5
Diet: Decaying leaves, biofilm, algae, detritus and leftover fish food.
Habitat: Best kept amongst leaf litter, mosses, aquatic plants, driftwood and stones.
Difficulty: Very easy.

A mix of adults and juveniles will be sent.

“A healthy pond is one where every creature has a purpose. Asellus aquaticus may be small, but they are among nature’s finest caretakers.”

Please ensure you choose 24hr tracked postage at checkout, since these are living creatures.