Rasboras, Boraras, and Microdevario: how to feed microfish in a natural aquarium
F. MattierFor several years now, we have witnessed the rise of nano-aquariums. These small volumes of water make it possible to recreate stunning aquatic landscapes on a simple desk. With them, tiny inhabitants have captured our hearts: Boraras brigittae, Microdevario kubotai, Danio margaritatus (the famous Galaxy Rasboras), and the small Nannostomus.
Yet once the initial wonder has faded, one reality becomes clear: finding food for micro-fish in an aquarium is often a real headache. In a small volume of water, sprinkling crushed flakes or broken-up pellets is an environmental disaster. These fish have microscopic mouths. They leave half of the dry fragments that fall to the bottom uneaten, and this industrial food decomposes within a few hours, ruining water quality and causing deadly pollution spikes.
It is time to change our approach.
Breaking the “meal” myth: the hunt continues just as it does in nature
We often project our own human habits onto our animals. The idea of “feeding time” at a fixed hour makes absolutely no sense for a miniature fish.
In their native streams and marshes, these fish do not eat large meals. They spend their days moving among dense plants in search of micro-prey invisible to the naked eye. This is their main occupation and the foundation of their mental and physical well-being.
The real biological solution is simple and fascinating: transform your nano-tank into a self-feeding environment where zooplankton coexists with the fish. The goal is to provide natural, live food for micro-fish that does not pollute the water because it lives there in perfect harmony until it is hunted.
The trick of resident breeding daphnia
This is where an absolutely brilliant ecological dynamic comes into play, one that I love setting up. We often think that introducing daphnia into a nano-aquarium will end in a five-minute massacre. That is false, provided you use the right daphnia size!
The secret is this: adult daphnia are simply too large to be swallowed by the tiny mouths of Boraras or Microdevario.
The result is magical: these “breeding” daphnia survive peacefully in the tank. They spend their time filtering the water (which improves its clarity) and, above all, they reproduce continuously. It is the newborn, tiny baby daphnia (nauplii) that will serve as prey for your fish. You no longer have one massive, polluting “meal,” but a multitude of natural micro-meals throughout the day, following the rhythm of the hatchings.
The living buffet adapted to tiny mouths
To stimulate the vitality and colors of your jewels, it is essential to vary their diet. Here are the ideal live prey items for creating a true plankton base and feeding a Boraras brigittae or any other dwarf fish:
Ostracods and daphnia
They form the perfect duo for creating this famous permanent plankton supply. Ostracods will clean the bottom and biofilm, while adult daphnia filter the water in full light, releasing their nauplii to the delight of your fish.
👉 Create your permanent plankton supply with our daphnia and microfauna cultures.
Vinegar eels and micro worms
Extremely fine, these tiny wriggling worms instantly trigger the fish’s hunting instinct. They are very easy to feed and are an ideal size for adult dwarf fish and young fry. To make it easy to raise food for nano-aquariums at home without any unpleasant odors, I designed the ZollaBox Baby. It allows you to cultivate your own micro worms cleanly. As for vinegar eels, we offer them ready to use and filtered.
👉 Become self-sufficient with the ZollaBox Baby.
👉 Discover our ready-to-use vinegar eel cultures.
Infusoria
If you are lucky enough to have spontaneous breeding in your nano-tank, newborn fry will need even smaller food: infusoria (single-celled organisms). The simplest and most economical way to produce them in large quantities is to steep untreated paddy rice in a container of water.
👉 Produce your own infusoria with our genuine paddy rice.
The setting: small plants to add complexity to the environment
A successful nano-tank is not just water and prey. Plants play a crucial microclimatic and architectural role.
In such a small volume, favor dwarf plants or fine-leaved varieties. Aquatic mosses, small cuttings of Limnophila, or floating plants with short roots create perfect refuges for plankton, allowing it to multiply safely. For your fish, these plants form a complex maze of vegetation that they will love exploring without ever getting bored. A well-planted tank is insurance against nitrate buildup and provides reassurance for fish that will display their most beautiful colors.
👉 Decorate your nano-tank with our suitable small plants.
Conclusion: a fascinating microscopic world
Observing a truly living nano-aquarium is a privilege. It means having a balanced, self-sufficient microscopic world before your eyes, where cellular life and plankton nourish the landscape. By replacing dead powders with a thriving ecology, you do more than avoid polluting your tank: you restore to your micro-fish their dignity as explorers and tireless hunters.
Mattier
FAQ: maintaining balance in a nano-aquarium
Which fish can be kept in a nano-aquarium without a filter?
In a small volume (20 to 30 liters) operated using low-tech methods (without a filter), you should choose extremely small species that produce little waste. Boraras brigittae, Microdevario kubotai, or very small killifish are excellent candidates. The important thing is not only the size of the fish, but above all to adapt the stocking level (very few individuals) to the abundance of your plant mass, which will act as a natural filter.
Could daphnia overrun the nano-tank?
Absolutely not! In a closed ecosystem, the daphnia population naturally regulates itself according to the amount of food available to them (phytoplankton and suspended bacteria). If the water becomes very clear, they will stop multiplying. In addition, your micro-fish will continuously pick off the newborns, maintaining the balance remarkably well.
How can you feed your micro-fish over a weekend?
That is the great advantage of natural aquaristics! If you have properly established your zooplankton cultures (ostracods, daphnia, micro worms) in a jungle of small plants, your nano-tank is completely self-sufficient. You can leave for a weekend with peace of mind: your fish will have plenty to hunt continuously among the mosses, without any intervention from you and without the risk of a pollution spike.