The 'top ten' on the Minifische website goes (it's translated from German so don't mind the language)...
Paedocypris progenetica - 8-9mm Cyprinidae P.progenetica is at present smallest vertebrate animal of the world and ranks among the Cypriniden. The discoverers are Maurice Kottelat et al. of that national University in Singapore. It shows some characteristics, which let it appear rather as a larva as an attained full growth animal. Picture: www.hexazona.com
Danionella of species Kristallbärbling > 1 cm Cyprinidae the kind Danionella contains only few kinds, which rank all among the smallest süsswasserfischen of the world. Very rarely in the trade. Picture: www.hexazona.com after www.danios.info
Pandaka pygmaea Zwerggrundel < 1.5 cmIUCN talking cunning CR Gobiidae males reach only 9 mm of length and 6 mg mass. P. pygmaea lives Singapore in rivers, Flussmündungen and Mangrovengebieten on the Philippines (Palawan, is considered there as become extinct), and in Indonesia (Bali, Sulawesi). It goes also into the Brack and sea water. Forms schools. Picture: Koichi Shibukawa www.kahaku.go.jp after www.wikipedia.de
Gobiopterus of species cf. panayensis - > 1.5 cm Gobiidae Found in quiet waters OF mangrove AREAs with softly muddy bottoms around aquatic plants; usually collected with the OTHER paedomorphic gobies OF the genus Pandaka. Koichi Shibukawa www.kahaku.go.jp
Oryzias minutillus Dwarf Reiskärpfling < 2 cm Adrianichthyidae the smallest Oryzias is often regarded as a young fish of other kinds. It is to be recognized easily by its blue eyes. In its homeland it was found also at temperatures around 35°C. Picture: www.hexazona.com
Scoloplax empousa Pantanal dwarf catfish < 2 cm Scoloplacidae dawn and night-active air-breather of the clear water zones, which looks in the soil reason for mosquito larvae u.ä and entrenches themselves when disturbances in the soil reason. Picture Ivan Sazima isazimaATunicampDOTbr Text after I.S. fishbase.org
Lepidarchus adonis Adonissalmler ~ 2 cm Alestiidae fastidious, attitude in small basins starting from 20cm with more closely planting and very soft water, finest living person and Trockenfutter. Picture: Aquarich Tsushimasuikaen aquarich.jp
Odontocharacidium aphanes Zorniger Zwergpfeilsalmler ~ 2 cm Crenuchidae Bedächtige floats, that keep themselves hidden in plants usually, however if necessary arrow fast by the water to tear can. Picture: Peter and Martin Hoffmann martinDOTpiranhaATwebDOTde after www.salmlernetz.de
Barboides gracilis - ~ 2 cm Cyprinidae Barboides gracilis, probably the smallest Cyprinide of Africa, is suitable outstanding for a society aquarium as well as other dwarf fish. Feeding and attitude proved as unproblematic. Michael Schlüter michaelDOTschlueterATweichwasserfischeDOTde
Boraras spec. “South Thailand†- ~ 2 cm Cyprinidae
You get the gist.
