Candidate
Bala shark
Balantiocheilos melanopterus
A huge, powerful schooling swimmer requiring public-aquarium scale planning.
- Adult
- 25–35 cm
- Minimum
- 600 L · 200 cm
- Group
- 5
Condition-led guide · reviewed 2026-07-31
Fish unsuitable for nano tanks
Small shop specimens and misleading common names conceal adults that need large groups, territories or long swimming runs.
Selection rules
What made the shortlist
- Plan from adult size and minimum length.
- Multiply social fish by their required group, not one specimen.
- Reject upgrade-later plans unless the larger aquarium already exists.
Real photographed species
Options worth researching
If the adult plan does not fit today, choose a species that does rather than relying on future rehoming.
Candidate
Clown loach
Chromobotia macracanthus
A long-lived social giant commonly sold as a small juvenile.
- Adult
- 25–35 cm
- Minimum
- 450 L · 180 cm
- Group
- 5
Candidate
Common pleco
Hypostomus plecostomus
An armoured catfish that can exceed many tanks' entire width.
- Adult
- 30–50 cm
- Minimum
- 450 L · 180 cm
- Group
- 1
Candidate
Oscar
Astronotus ocellatus
A bulky territorial cichlid with heavy waste output.
- Adult
- 30–35 cm
- Minimum
- 300 L · 120 cm
- Group
- 1
Candidate
Senegal bichir
Polypterus senegalus
A predatory, escape-prone fish needing length and secure cover.
- Adult
- 25–35 cm
- Minimum
- 300 L · 120 cm
- Group
- 1
Candidate
Congo tetra
Phenacogrammus interruptus
Even this 'tetra' needs a long aquarium and a substantial shoal.
- Adult
- 6–9 cm
- Minimum
- 150 L · 100 cm
- Group
- 8
Candidate
Rainbow shark
Epalzeorhynchos frenatum
Territory and swim length exclude small community tanks.
- Adult
- 12–15 cm
- Minimum
- 150 L · 120 cm
- Group
- 1
Candidate
Boesemani rainbowfish
Melanotaenia boesemani
An active group requires far more length than a nano provides.
- Adult
- 7–11 cm
- Minimum
- 200 L · 120 cm
- Group
- 8
Common mismatch
Actual nano-scale alternatives
The 'avoids' section here is deliberately reversed: it shows genuine nano-scale alternatives, not tank mates for the large fish above.
Think again
Betta fish
Betta splendens
A single betta is one of the few fish plans possible in a properly heated 20 litre minimum setup.
- Adult
- 5–7 cm
- Minimum
- 20 L · 45 cm
- Group
- 1
Think again
Chili rasbora
Boraras brigittae
A full group can work in a mature 45 cm nano designed around the species.
- Adult
- 1.5–2 cm
- Minimum
- 35 L · 45 cm
- Group
- 10
Think again
Ember tetra
Hyphessobrycon amandae
A generous group fits only once its 45 cm footprint and water needs are met.
- Adult
- 1.5–2 cm
- Minimum
- 45 L · 45 cm
- Group
- 10