The word "undemanding" in a fish description says nothing about how much water the fish needs. The pearl gourami, often recommended to beginners, is listed in the catalogue at 140 litres per group.

Which fish suit a beginner depends on three things: the volume of your aquarium, the water from your tap and the number of fish the species needs to be kept with. Looks do not come into it.

What the "For beginners" category includes

The catalogue has a category, For beginners, with 39 species and forms. These are fish that are directly recommended to a beginner. They include danios, barbs, rasboras, tetras, corydoras, platies and their relatives, the pearl gourami, Anomalochromis thomasi and the marbled catfish. Fifteen entries are colour forms of the platy, so there are fewer species than it seems.

The recommended volume for these fish is 50 to 140 litres. For 21 entries it is no more than 60 litres, for 36 no more than 80.

The main caveat: the volume is for a group

The recommended volume is not "per fish". It is the volume for the whole group the species should be kept in. If a corydoras is listed with a group of 5–6 fish and 70 litres, then 70 litres is needed for all six together.

For platies no group size is given. There is one rule of thumb: keep more females than males, otherwise the males give the females no peace.

A shoal is not a whim. Danios bought singly or in a pair become timid and sluggish. For this species, take no fewer than 8–10 fish.

Hence the rule: buy a group, not a single fish, and work out the volume for the group.

Nine species with numbers

Temperature and size are for adult fish in an aquarium.

  • Zebra Danio (Danio rerio) — 4–5 cm, 18–24 °C, 80 litres. Peaceful and active. A shoal of at least 8–10 fish. The aquarium needs a lid: danios jump.
  • Cherry Barb (Puntius titteya) — 5 cm, 23–26 °C, 54 litres. Peaceful. A shoal of 6–10 fish.
  • Glowlight Tetra (Hemigrammus erythrozonus) — 4 cm, 23–28 °C, 60 litres. Peaceful, stays in the middle layers of the water. A shoal of 6–10 fish.
  • Bronze Corydoras (Corydoras aeneus) — 7 cm, 21–27 °C, 70 litres. A peaceful bottom-dweller, in a group of 5–6 fish. Lives up to 10 years.
  • Panda Corydoras (Corydoras panda) — 4 cm, 20–25 °C, 50 litres, a group of 5–6 fish. Peaceful, bottom-dwelling. In water warmer than this range it lives noticeably less long.
  • Common Platy (Xiphophorus maculatus) — 5–7 cm, 20–28 °C, 60 litres. Peaceful, stays near the surface. It needs alkaline, hard water: pH 7–8.2, hardness 10–30 dGH.
  • Pearl Gourami (Trichopodus leerii) — 10 cm, 23–28 °C, 140 litres, a group of 5–6 fish. Peaceful, lives near the surface. It is a labyrinth fish: it gulps air at the surface, so the aquarium is kept covered with a lid.
  • Anomalochromis thomasi — 8 cm, 23–27 °C, 80 litres. Peaceful, modest and shy. It can be kept alone or in a small group.
  • Marbled Catfish (Amblydoras nauticus) — 7 cm, 23–28 °C, 50 litres, a small group of 3–4 fish. Peaceful, but it may eat a very small fish. Active at night, hides by day.

This is an example, not a ranking. The other species in the category are in the catalogue.

How to choose fish in the shop

These signs work for any species.

  • Watch for activity. A healthy fish is mobile and reacts to what is going on around it. Do not take fish that lag behind the shoal or look emaciated.
  • Examine the fins and body. Damaged fins, white spots or a film are a reason to walk away. Clear eyes and the absence of sores matter too.
  • Ask for the fish to be fed. Healthy fish show interest in food. A sunken belly is a sign of emaciation.
  • Ask about quarantine. It is best to keep new fish at home in a separate container for at least two weeks.

What to do before buying fish

  1. Find out the volume of your aquarium and compare it with the recommendations. If you have less than 50 litres, choose with particular care: there are no species in this category with a lower recommended volume. For why a small volume is harder than a large one, see the article A 10–20 litre aquarium.
  2. Test your tap water. You need pH and general hardness (dGH). The platy needs hardness of 10–30 dGH, the panda corydoras 1–12 dGH. More in the article Water chemistry.
  3. Choose a species whose water and temperature match yours.
  4. Run the aquarium without fish. This usually takes three to six weeks, until ammonia and nitrite stay at zero. The procedure is in the article Starting an aquarium and the nitrogen cycle.
  5. Check the company. You can check a pair of species in the compatibility section, and work out the volume and equipment for a group with the calculator. How to judge tank mates yourself is in the article Fish compatibility: choosing tank mates.
  6. Buy the first batch, not all the fish at once. The bacterial colony grows to match the load, and ten new fish at a time cause an ammonia spike.
  7. Feed once or twice a day, a portion for one to two minutes. For bottom-dwellers, sinking tablets after the lights go out. See Feeding aquarium fish.

What does not help

  • Choosing by looks. The pearl gourami is beautiful, but it is listed at 140 litres. A goldfish, as the article on small aquariums says, needs hundreds of litres. Look at volume and water, not at photos.
  • The smallest aquarium "to start with". The less water, the faster it spoils. If you have not chosen yet, a 40–60 litre aquarium is more forgiving of mistakes than a fifteen-litre one.
  • One fish instead of a shoal. For shoaling species this is not a saving but stress.
  • The idea that "tropical fish live together". Danios need 18–24 °C, the pearl gourami 23–28 °C. Their common band is 23–24 °C, just one degree. Compare ranges rather than memorising "tropical fish".
  • Starting "with fish". For several weeks a living creature spends its time in water with ammonia. Medicines in a new aquarium hit the bacteria you are trying to grow.

In short

A first aquarium is volume, tap water and a shoal, not a particular species. First count the litres and test the water, then choose the fish.

If the aquarium is already set up, start with the cycle: Starting an aquarium and the nitrogen cycle. If you are still choosing a size, read A 10–20 litre aquarium, which says plainly what you must not do in a small volume.