Nanofish by suitability for tank size

1 gallon

Labyrinth Fish:
Siamese Fighting Fish / Betta (Betta splendens)

Gobies:
Bumblebee Goby (Brachygobius sp.)
Schooling Bumblebee Goby (Brachygobius aggregatus)

Livebearers:
Endler's Livebearer (Poecilia wingei)

2 gallons

Labyrinth Fish:
Pygmy/ Sparkling Gourami (Trichopsis pumila)
Honey Gourami (Colisa chuna)
Sunset Gourami (Colisa chuna)

Plus fish with suitability for smaller tanks

3 gallons

Labyrinth Fish:
Dwarf Bettas (Betta sp. coccina, tussyae, edithea, rutilans, persephone, etc.)

Rasbora:
Pheonix Rasbora (Boraras merah)
Chili Rasbora (Boraras micros)
Dwarf Rasbora / Pygmy Spotted Rasbora (Boraras maculatus)
Exclamation Point Rasbora / Sparrow Rasbora (Boraras urophthalmoides)
Mosquito Rasbora (Boraras brigittae)
Microrasbora kubotai
Microrasbora nana

Livebearers:
Guppies (Poecilia reticulata)

Plus fish with suitability for smaller tanks

4 gallons

Killifish:
Clown killie (Epiplatys annulatus)
Least Killifish (heterandria formosa)

Livebearers:
Guppies (Poecilia reticulata)
Endler's Livebearer (Poecilia wingei)
Barred Livebearer / Banded Widow / Stuart's Livebearer (Carlhubbsia stuarti)
Carnegie's Millionsfish/Livebearer / Ten-Spotted Live Bearer (Cnesterodon carnegiei)
Teardrop Mosquitofish / Tropical Mosquitofish / Bandit Mosquitofish (Gambusia sexradiata)
Grand Cayman Limia (Limia caymanensis)
Limia dominicensis
Limia rivasi
Sulphur Limia (Limia sulphurophila)
Neoheterandria cana CA
Tiger Teddy (Neoheterandria elegans)
Picotee Livebearer / Fairweather/Elegant Widow (Phallichthys fairweatheri)
Four-Spot / Domino Widow (Phallichthys quadripunctatus)
Pallid Widow (Phallichthys tico)
Dusky Millions Fish / Caudo (Phalloceros caudimaculatus)
Phalloptychus januarius
Poecilia amazonica
Branner's Livebearer / Ocellated Micromolly (Poecilia branneri)
Cauca Molly / South American Molly (Poecilia caucana)
Dwarf Molly (Poecilia chica)
Caracas Livebearer / Dwarf Limia, Haiti Limia / Venezuela-Molly (Poecilia heterandria)
Poecilia minima
Poecilia minor
Poecilia sulphuraria
Poeciliopsis baenschi
Poeciliopsis monacha
Blackstripe Livebearer (Poeciliopsis prolifica)

Tetras: Ember tetra (Hyphessobrycon amandae)

Plus fish with suitability for smaller tanks

5 gallons

Labyrinth Fish:
Pygmy/ Sparkling Gourami (Trichopsis pumila)

Minnows:
Vietnamese Minnow / Dwarf Cardinal (Tanichthys micagemmae)
Barboides gracilis

Pencilfish:
Dwarf Pencilfish (Nannostomus marginatus)

Chiclids:
Similis Ciclid (Neolamprologus similis)

Corys:
Dwarf Cory (Corydoras hastatus)
Pygmy Cory (Corydoras pygmaeus)

Catfish:
Oto (Otocinclus affinis)

Rasbora:
Neon Rasbora (Sundadanio axelrodi)
Green-eye Rasbora (Rasbora dorsiocellata)

Killifish:
Adamas
Aphyoplatys
Campellolebias
Congopanchax
Cynopoecilus
Diapteron
Fluviphylax
Foerschichthys
Fundulosoma
Yucatan flagfish (Garmanella pulchra)
Leptolucania
Catarina Pupfish (Megupsilon aporus) Micropanchax
Pantanodon
Plesiolebias
Stenolebias
Terranatos
Tomeurus
Magnificus Killi (Simpsonichthys magnificus)
lampeye killies
Rivulus

Tetras:
Flame Tetra (Hyphessobrycon flammeus)
Black Neon Tetra (Hyphessobrycon herbertaxelrodi)
Black Phantom Tetra (Hyphessobrycon megalopterus)
Red-Tailed Phantom Tetra (Hyphessobrycon roseus)
Hyphessobrycon eques
Ruby tetra (Axelrodia riesei)
Green Neon tetra (Paracheirodon simulans)
Jellybean tetra (Lepidarchus adonis)
Silvertip tetra (Hasemania nana)
Royal tetra (Inpaichthys kerri)
Jewel tetra (Hyphessobrycon eques)
Blackline Penguinfish (Thayeria boehlkei)
Red phantom tetra (Hyphessobrycon sweglesi)
Flag tetra (Hyphessobrycon heterorhabdus)
Neon Tetra (Paracheirodon innesi)
Glow Light Tetra (Hemigrammus erythrozonus)
Pristella Tetra (Pristella maxillaris)

Misc. Fish:
Neolebias ansorgii
Hara jerdoni

Plus fish with suitability for smaller tanks

6 gallons

Catfish:
Hummingbird catfish
Shadow Catfish (Hyalobagrus flavus / Pelteobagrus ornatus)
Mini Moth Catfish (Hara jerdoni)
Burmese Mini Catfish (Ereithes conta)

Plus fish with suitability for smaller tanks

7 gallons

Puffers:
dwarf puffer (Carinotetraodon travancoricus)

Plus fish with suitability for smaller tanks

8 gallons and 9 gallons

Fish with suitability for smaller tanks

10 gallons

Labyrinth Fish:
Red Licorice Gourami Parosphromenus sumatranus (Parosphromenus deissneri)
Licorice Gourami (Parosphromenus deissneri)

Pencilfish:
Dwarf Pencilfish (Nannostomus marginatus)

Corys:
Smudge-spot Cory (Corydoras similis)
False Cory (Aspidoras pauciradiatus)

Danios:
Glow Light Danio (Danio choprae)

Barbs:
Barbus sylvaticus
Jae barb (Barbus jae)
Lipstick Barb (Puntius sealei)
Dwarf Gold Barb (Barbus gelius)

Livebearers:
Xiphophorus continens
Monterrey Platyfish (Xiphophorus couchianus)
Northern Platyfish (Xiphophorus gordoni)
Southern Platy (Xiphophorus maculatus)
Catemaco Platyfish (Xiphophorus milleri)
Pygmy Swordtail (Xiphophorus pygmaeus)
Swordtail Platyfish (Xiphophorus xiphidium)

Rainbowfish:
Gertrude's Rainbow/ Gertrude Blue-eyes (Pseudomugil gertrudae)
Threadfin Rainbows (Iriatherina werneri)

Misc. Fish:
Scarlet Badis (Dario dario)
Orange Chela (Chela dadyburjori)
Asian Rummynose (Sawbwa resplenden)
Peacock gudgeon (Tateurndina ocellicauda)

Plus fish with suitability for smaller tanks