In nano tanks you don’t have as much choice of fish as in normal sized aquariums. Nevertheless, there are some beautiful animals, so-called nano fish, which can also live well in an aquarium with 20-30l, if the setup for the fish fits and you do not put too many of them in.

Axelrodia riesei – Red semolina tetra

Barboides gracilis

Boraras brigittae
Boraras maculatus – Dwarf danio
Boraras merah – Gold spotted dwarf danio
Boraras micros – Microrasbora
Boraras urophthalmoides – Long-banded dwarf danio
Boraras naevus – Strawberry dwarf danio

Corydoras hastatus – Sickle spot dwarf armored catfish
Corydoras habrosus – Checkerboard dwarf armored catfish
Corydoras pygmaeus – Dwarf armored catfish

Danionella (various)

Elassoma evergladei – Dwarf Black Perch
Elassoma okefenokee – Okefenokee Dwarf Black Perch

Hara jedoni – Delta wing dwarf catfish

Heterandia formosa – Dwarf carp

Hyphessobrycon amandae – Sparkling tetra
Hyphessobrycon elachys – Reed tetra

Neoheterandria elegans – Teddy carp

Neosthethus lankesteri

Oryzias javanicus – Javanese Carp
Oryzias mekongensis – Mekong Rice Carp
Oryzias minutillus – Dwarf Rice Carp

Betta Splendens – Siamese fighting fish
Betta mahachaiensis – Mahachai fighting fish
Betta smaragdina – Emerald fighting fish
Betta tussyae – Red fighting fish
Betta miniopinna
Betta persephone – Foliage dwarf campfish

Trichopsis Pumila – Growling dwarf gourami

Parosphromenus nagyi – Black dwarf gourami
Parosphromenus ornaticauda – Jewelry Magnificent Gurami

Aphyosemion (various)
Fundulopanchax amieti – Amiets splendid carp
Rivulus (various)
Epiplatys annulatus – Ringlet pike

Zoogeneticus tequila – Tequila carpets

Poecilia caucana – Cauca Molly
Poecilia wingei – Endler guppy

Barbus jae
Barbus hulstaerti – Butterfly barb
Microdevario kubotai – Emerald Dwarf Grassbora
Danio tinwini – Dwarf leopard danio
Sundadanio axelrodi – Axelrod’s bear

Aspidoras pauciradiatus – Spotted dwarf armored catfish
Tatia perugiae – Reticulated Thorn Catfish

Oryzias latipes – Medaka

Brachygobius doriae – Golden Ringed Goby
Gobiopterus chuno – Glass goby

Elassoma (various)
Dario dario – Dwarf Bluefish

In addition, in such aquariums always fit dwarf shrimp and snails. However, with dwarf shrimp there is to note that certain fish hunt and kill them.

Source: Aquariumforum.de