Corydoras catfish are wonderful fish, but the most common species, such as the Bronze Corydoras and the Peppered Corydoras, grow too large for tanks of much under ten gallons if you’re to keep them in a group. Since Corydoras are schooling species and prefer to be in groups, it is good that there are smaller species available. All of the species listed below are under 2 inches when fully grown.

Small Corydoras Species:

C. osteocarus 1.8in
C. tukano 1.8in
C. melini 1.8in
C. breei 1.8in
C. boesemani 1.8in
C. bicolor 1.8in
C. sanchesi 1.6in
C. paragua 1.6in
C. ortegai 1.6in
C. multimaculatus 1.6in
C. gracilis 1.6in
C. lamberti 1.5in
C. paucerna 1.4in
C. habrosus 1.4in
C. cochui 1.4in
C. pygmaeus 1.3in
C. hastatus 1.3in

Sources:

Planet Catfish for species lengths.