The Medaka Fish: Why It’s the Absolute Star of Small Outdoor Ponds
F. MattierIf you mention a garden pond to a beginner, the first images that come to mind are often large koi carp gliding beneath water lilies or goldfish darting in clear water. Yet, the reality on the ground is often quite different. Maintaining these large fish requires substantial volumes. In confined spaces, their extreme density, the staggering accumulation of their waste, their high oxygen consumption, and the tremendous pressure they exert on the environment (total predation, uprooted or eaten plants) quickly turn the pond into an aquatic desert.
But what if the true king of the garden isn’t who we think? For several years, a small fish from the East has challenged all our certainties and established itself as the ethical and ecological solution par excellence for small spaces: the Medaka. Let me explain why this little prodigy has become my absolute passion.
The Medaka, the anti-goldfish: an ethical plea
I strive to deliver a clear message: the goldfish is a space-demanding animal. A single individual requires at least a hundred liters of water to live decently. Yet, the temptation is strong to want to introduce life into a small terrace pond, a half-barrel, or a simple 80-liter poubellarium. Housing a goldfish there is an ecological mistake and an act of unintentional cruelty. In summer, facing high heat, these small volumes turn into boiling pots where the large goldfish quickly suffocates.
This is where the Medaka changes the game for animal welfare. Where the goldfish suffers and withers, the Medaka thrives fully. Thanks to its small size (about 3 to 4 centimeters at adulthood) and its metabolism perfectly adapted to calm waters, a small group of Medakas can live a rich, natural, and stress-free life in a volume where a goldfish would perish in a few weeks.
Even better: the small size of the Medaka offers a huge ecological advantage for the balance of the environment. The goldfish is a destructive glutton that eats absolutely everything it finds, including your precious cleaning snails and the water lice responsible for recycling the mud. The Medaka is physically incapable of this. Its tiny mouth keeps your precious detritivore army intact. The water lice and snails can work and multiply safely alongside it, ensuring the tank stays clean. Adopting the Medaka means rejecting unsuitable confinement to choose respect for life and a functional ecosystem.
👉 Learn more about the goldfish scandal.
Identity card of a survivor from Japanese rice fields
The Medaka (Oryzias latipes) is not a laboratory fish. It is an authentic rice field fish, shaped by millennia of evolution in the stagnant, shallow waters of Japan. This geographic origin gives it the status of a true survivor.
Visually, it is enchanting. Unlike typical aquarium fish viewed from the side, the Medaka has been bred by Japanese breeders to be admired from above (Top View). When you lean over your pond, you discover living jewels in multiple varieties:
- the sparkling purity of Miyuki with their iridescent metallic blue dorsal line,
- the pearly softness of Youbi,
- and the glittering reflections of the Lame strains.
A fish resistant to heatwaves and frost
What makes the outdoor Medaka fish such an exceptional choice is its extraordinary resilience. Used to the brutal temperature swings of rice fields, it is an incredible fish resistant to heatwaves. It tolerates waters nearing 30°C in the height of summer without flinching, where other species would suffocate.
Even better: you can raise Medakas outdoors all year round. As soon as autumn arrives, its metabolism slows down. It enters lethargy and spends the winter under the ice without any problem in our western regions, provided the bottom of your pond or poubellarium does not freeze solidly through.
A unique reproduction: the poetry of life
Watching life continue is one of the greatest joys of natural aquaristics. In this regard, witnessing the Medaka reproduction in a pond is an absolutely poetic spectacle.
Every summer morning, if food is abundant and the water warm, females display a cluster of perfectly spherical and translucent eggs suspended from their abdomen. They swim like this for several hours, showing off their precious burden. Then begins a delicate ballet: the female slips into the maze of vegetation to brush and stick her eggs one by one against the stems and roots of plants.
Killifish enthusiasts know this behavior well and often use artificial "mops" (tufts of synthetic wool suspended) to collect eggs. The Medaka, however, much prefers the natural. It performs this delicate work right in the heart of your plants. This is why a regular supply of live food is essential. Distributing small amounts of daphnia or Grindal worms instantly stimulates their wild hunting instinct and triggers massive daily spawning.
👉 Order our live daphnia strains to boost your Medaka spawnings.
The poubellarium: your garden’s best mosquito trap
We all seek solutions to control the biting mosquitoes that ruin our summer evenings, not to mention the growing problem of the tiger mosquito that strikes even during the day. Installing a pump-free Medaka in a planted poubellarium is the most formidable biological control method there is. It is a truly 100% natural tiger mosquito trap (and for common mosquitoes too!).
Attracted by the calm water of the poubellarium, the female mosquito comes to lay her eggs, thinking she is offering a safe haven for her offspring. In reality, she signs their immediate death warrant. Thanks to its small size and incredible agility, the Medaka is infinitely more nimble than a clumsy large goldfish. It slips into every nook and cranny, swims in very shallow marshy areas, and darts under leaves to methodically gobble up every larva as soon as it hatches.
👉Learn more about the poubellarium.
A vegetal maze for the fish’s pleasure and balance
To offer a worthy life to your Medakas, you must recreate their original ecosystem. The Medaka is a rice field fish: it has a vital need for an environment extremely dense in vegetation.
I recommend combining three types of plants to create a true aquatic jungle:
- Oxygenating plants (such as Hornwort or Elodea): they form a dense submerged carpet where freshly hatched fry will find immediate refuge to escape adult curiosity.
- Floating frogbit: with its long, hanging, feathery roots, it is the natural spawning support preferred by female Medakas.
- Surface plants (such as large duckweed or Azolla): they are ideal for creating precious shaded and cooling areas.
This vegetal maze allows alternating very bright zones and cool shaded areas where fish retreat to rest. Offering these ecological variations is essential for their pleasure, sense of security, and psychological balance—concepts that are crucial in my eyes.
👉 Discover our oxygenating plants ideal for Medakas.
Conclusion: choose a living and ethical garden
Adopting the Medaka means breaking with preconceived ideas to return to common sense. It means choosing a living, aesthetic garden that is incredibly useful for regulating mosquitoes and deeply respectful of the true nature of fish. This summer, forget cramped goldfish: set up a planted poubellarium, introduce a small group of Medakas, and let the magic of life work.
Mattier
FAQ: Your questions about raising Medaka
How many Medakas in an 80-liter poubellarium?
For a well-planted volume of 80 to 100 liters installed outdoors, you can confidently start with a small group of 6 to 8 individuals (ideally with more females than males). It is a gregarious fish that needs to live in a group to feel secure and display natural behavior.
What food should be given to Medaka fry?
At birth, the fry are tiny and float just below the water surface. In a natural tank, they will already find a significant amount of microfauna. Instead of using industrial powders for fry, the ideal is to distribute live prey raised at home, such as vinegar eels or springtails. Vinegar eels will delight the fry, while the smaller springtails will please the growing juveniles, and the larger ones serve as aerial treats for adults to stimulate their hunting instinct.
Can they be left outside all year round?
Yes, absolutely! This is one of the great strengths of this species. Medakas tolerate winter temperatures without flinching. The only imperative condition is that your container (pond or poubellarium) has a depth of at least 40 to 50 centimeters. This way, even if a thick layer of ice forms on the surface, the water remains liquid at the bottom, allowing the fish to spend the winter in slow motion waiting for spring.