Pygmy Corydoras (Corydoras pygmaeus): Nano Shoal Care

Corydoras pygmaeus (pygmy corydoras) is a freshwater catfish best understood through its adult size, feeding surface, and social behaviour rather than the shop label "bottom feeder". In aquaria it reaches 2.5–3 cm and does best when the whole tank is designed around clean substrate, stable water, and enough conspecifics to behave normally.

Part of the Complete Catfish Guide.

Identification

A dark lateral stripe runs from snout through tail with a pale belly and translucent fins. The small adult size separates it from juvenile corydoras sold at similar length. Females become visibly rounder but remain tiny.

Good identification prevents two common mistakes: buying a fish that will not fit the aquarium, and copying a care sheet written for a superficially similar species. Compare closely with bronze corydoras, otocinclus, and glass catfish when choosing stock.

Origin & Habitat

Madeira and Paraguay basin tributaries, usually in quiet marginal vegetation. Pygmy corydoras inhabit margins, plant thickets, and quiet shallows where fine detritus and microcrustaceans collect. They are not high-flow fish, and they are easily stressed by bare tanks with bright light.

Natural habitat is not a decorative theme. It tells the aquarist what the fish contacts all day: sand or rock, leaf litter or current, shaded margins or open water. For this species the useful aquarium translation is mature biological filtration, no detectable ammonia or nitrite, nitrate preferably below 20 mg/L, and a feeding zone that stays clean between meals.

Aquarium Husbandry

Keep pygmy corydoras in 45 litres for 10–12 if mature and well planted; 60 litres is easier. Use the parameter range in the table, and avoid sudden swings in hardness or temperature. If tap water is very hard, blending with reverse-osmosis water is safer than repeated acid dosing; the chemistry behind that choice is covered in water hardness explained.

For corydoras-like substrate feeders, fine rounded sand is strongly preferable to coarse gravel. Gravel traps food below reach, abrades barbels, and creates bacterial pockets exactly where the fish pushes its mouth. The practical substrate trade-offs are covered in substrate selection. In planted tanks, shaded cover from anubias nana or java fern helps nervous fish forage in daylight without requiring high light.

Filtration should be mature rather than violent. Surface movement, clean mechanical media, and regular water changes are more useful than a high turnover number that blasts food away. Add this fish only after the aquarium is cycled; cycling a new aquarium is the relevant care reference.

Tankmates & Behaviour

This is the corydoras exception most aquarists notice: the shoal spends much time mid-water, hovering on plant edges, then drops to the sand to feed. Keep them with ember-sized tetras, small rasboras, shrimp-safe fish, and peaceful anabantoids rather than large gouramis or cichlids.

Suitable tankmates are peaceful fish that share temperature and hardness needs. Small characins from the complete tetras guide are often better companions than boisterous barbs or territorial cichlids. If cichlids are present, check the water chemistry and territorial pattern in the complete cichlids guide before assuming a bottom fish will be ignored.

Diet

Food size controls success. Use powdered sinking food, crushed micro-granules, baby brine shrimp, microworm, cyclops, and fine frozen foods. Full-sized tablets become feeding stations for snails and larger fish before pygmies can use them.

Feed after the surface fish have slowed down, or use several small feeding points so the group is not crowded into one corner. A thin-bodied fish with a pinched belly is already losing condition. Conversely, tablets left to dissolve for hours create the bacterial load that damages barbels and gills.

Breeding

Well-conditioned adults scatter a few adhesive eggs daily or in small waves. Eggs are often placed on glass, moss, or the underside of leaves. Dense moss and low predation allow some fry to appear without intervention.

Conditioning means clean water and varied food, not simply more food. Spawning aquaria should be easy to inspect, with an air-driven sponge filter, fine sand or bare glass, and removable spawning mops or broad leaves. Fry are sensitive to stale micro-food, so small daily water changes are safer than heavy feeding.

Common Problems

Starvation in community tanks is common because the fish are too small to compete. Intake guards are mandatory on strong filters. Do not combine with pictus catfish, angelfish, or any mouth large enough to test them.

Quarantine is worthwhile even for hardy-looking specimens. Many catfish are transported thin, crowded, and underfed. Observe breathing rate, barbel condition, belly profile, and willingness to take food before adding them to a display aquarium.

Buying, Quarantine, and Observation

Select specimens with intact fins, clear eyes, steady breathing, and a body profile appropriate to the species. For corydoras, inspect barbels and the underside of the mouth; for loricariids, look for sunken bellies or hollow eyes; for active predatory catfish, reject individuals with abraded snouts from crashing into glass. A fish that is cheap because it looks thin is rarely a bargain.

Quarantine should reproduce the display tank's basic conditions rather than being an empty punishment box. Use seeded filtration, cover, and the correct first foods. Watch the fish feed at least several times before release. If it will not eat in a quiet quarantine tank, it will not improve in a competitive community. Early correction is easier than recovering a catfish after several weeks of hidden weight loss.

See Also

• The Complete Catfish Guide
• bronze corydoras, otocinclus, and glass catfish
• anubias nana and the complete anabantoids guide
• Cycling a New Aquarium