Corydoras Care: Why School Size Matters More Than Most People Think

A social species, not a decoration

Corydoras are highly social schooling fish — in the wild they're found in groups numbering dozens to hundreds. A pair or trio in a home aquarium is the bare minimum, and even that minimum produces visibly different (more skittish, less active) behavior than a proper school of 6+.

What undersized groups actually look like

Corys kept in groups of 2–3 often hide more, eat less actively, and show duller coloration than the same species in a school of 6 or more — chronic low-grade stress from inadequate group size, not illness.

Practical stocking guidance

• Minimum: 6 individuals of the same species
• Better: 8–10, especially for smaller species like pygmy or habrosus cories
• Tank size: most cory species need at least 20 gallons for a proper school, given their footprint requirements and the bioload of 6+ fish

A common mistake worth naming

Mixing 2 of one cory species with 2 of another doesn't satisfy the social need — cories generally school most readily with their own species, so a "school" of mixed singles/pairs often behaves like several isolated small groups rather than one cohesive school.