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An atlas of small worlds

A big world on the other side of the glass.

Fish, plants and everything that helps them live together.

Open the fish atlasCheck compatibility

1,249 fish species277 plant species

Your aquarium comes first.

Enter its parameters and the catalogue will keep the species they suit.

Suitable water does not mean the fish will get along: pairs are checked separately.

Every species has a story.

Explore the atlas

Who gets along with whom?

Check the neighbours before you stock the tank.

Understand your aquarium

Cycling, water, plants and algae — step by step, without excess theory.

Read the articles

What's inside

The sections are linked: from a species card you can see who it will live with, which plants it will leave alone and how much water it needs.

What is known about every species

  • A shoaling species, a pair or a loner — and how many individuals it takes for the fish to behave calmly. Volume is given for that group, not for one fish.

  • What to feed and how often, whether it needs plant matter, and what does not suit this species.

  • Jumping, danger to smaller tank mates, demands on flow and substrate — the things you find out late and expensively.

  • How the species breeds, what spawning takes, and how long it lives under decent care.

Where to start with an aquarium

  1. Settle the volume

    If you already have a tank, measure it. If not, the calculator works it out from the dimensions. This alone rules out half the catalogue.

    Open the calculator

  2. Pick the residents

    Enter your volume, temperature and water hardness in the filter — the catalogue keeps only the species they suit.

    Open the catalogue

  3. Check they will get along

    The matrix shows pair by pair who will eat or harass whom. Cheaper to learn here than in the tank.

    Check a pair

Common questions

How many fish fit in a 20-litre tank?

It depends on the species, not on the number. 15 species in the catalogue are fine in twenty litres; the rest need more. And the volume on a card is given for a group the species lives in properly, not for a single fish.

Which aquarium fish are the easiest to keep?

The catalogue has a separate beginner category — 39 species reckoned the most forgiving of a newcomer’s mistakes. That does not mean no preparation is needed: they still have their own volume, temperature and tank mates.

Which aquarium fish get along together?

It is settled pair by pair, not by a list of peaceful species. The compatibility matrix covers 510 species and gives every pair one of three verdicts — compatible, with care, not recommended — along with the reason. Most often the trouble is a difference in size, temperament or water requirements.

How do you work out aquarium volume?

From the internal dimensions: length × width × height, less the substrate. The calculator does it for you and also suggests heater wattage and filter throughput.

What has to be done before adding fish?

Let the tank settle with the filter running. The bacteria that process ammonia do not appear at once — it usually takes a few weeks. There is a separate article on the nitrogen cycle.

Aquario — Your Trusted Guide to the World of Aquarium Fish

Dreaming of creating the perfect aquarium but don't know where to start? Looking for new inhabitants for your underwater world? Aquario is your personal assistant in the world of aquaristics!

The catalogue is built so that the numbers can be acted on. Volume is given for a group the species is comfortable in, not for a single fish; temperature and pH are working values, not the extremes a fish will survive.

Where there was no certainty, the card carries a caveat rather than an averaged number. Better to say nothing than to say something that costs a fish its life.

The sections lead into one another: from a fish card you can move to its tank mates, to the plants it will not touch, and to the article on what to feed it. That is what a handbook is for — not a list of species, but answers to the questions in the order they come up.

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