Pygmy cory

Water parameters

Tolerated range for this species. Aim for the middle of each band rather than the extremes.

Tank and habitat

Substrate: sand.

Behavior

Plant interaction: plant safe.

Feeding

Tiny mouths require tiny food. Micro pellets, crushed flake, frozen baby brine shrimp, frozen cyclops, frozen daphnia, and live microworms or vinegar eels are the core diet. Standard-size pellets and wafers are too large; they'll pick at the surface but can't break off meaningful pieces. In community tanks, they're easily outcompeted and need targeted feeding. Drop micro food directly into their schooling area. They feed in the midwater column more than on the substrate, which is unusual for a Corydoras and means sinking food isn't always the right strategy. Two to three feedings daily in very small amounts works best.

Compatibility

• One of the three "dwarf cory" species regularly sold in the hobby (the others are C. hastatus and C. habrosus). Pygmy corys are the most commonly available and differ from the other two in that they spend more time in the midwater column than on the substrate.
• Safe with everything that won't eat them. The main risk is being housed with fish large enough to swallow them. Anything with a mouth wider than 1.5 cm is a threat. Stick with nano fish: ember tetras, chili rasboras, celestial pearl danios, and shrimp.
• Groups of 10+ are the minimum for natural behavior. They school in the midwater, hover in one spot, then dart as a group to a new spot. Smaller groups hide constantly. 15-20 in a planted nano tank is ideal.
• Excellent inhabitants for shrimp tanks. They ignore shrimp completely (adults and shrimplets) and add activity to a level of the tank that shrimp don't occupy.

Origin and habitat

Corydoras pygmaeus, the pygmy cory, recently moved to the genus Gastrodermus, is the smallest of the corydoras catfishes and one of three tiny dwarf corys in the hobby alongside C. hastatus and C. habrosus. Knaack described it in 1966. It comes from soft, acidic, often tannin-stained waters of western Amazonia, with the Madeira basin as the type area and records from the Nanay in Peru and the Aguarico in Ecuador. It is told apart from the similar C. hastatus by a dark stripe that runs the full length of the flank, where hastatus has only a diamond-shaped spot at the tail base; many older records of hastatus turned out to be misidentified pygmy corys. The standout behaviour is that, unlike most bottom-hugging corydoras, the pygmy cory spends much of its time hovering in midwater, flapping its fins like a tiny underwater hummingbird, though it also forages on the bottom and on leaves. Like all corydoras it is an armoured catfish, protected by bony plates rather than scales, and it reaches only about 2.5 cm. An albino form is traded. It is strongly schooling and does best in groups of ten or more.

Breeding

Breeds along corydoras lines, set off by a cool water change after conditioning a good-sized group on rich foods. Using the genus T-position, the female holds a couple of eggs between her pelvic fins while the male fertilises them, then swims off to glue each sticky, roughly millimetre egg singly onto a leaf, the glass, or decor, repeating until she has placed a few dozen up to around a hundred over a session. The eggs hatch in three to four days, and the fry are minute and need infusoria-grade food before baby brine shrimp. In a thickly planted nano tank with moss and leaf litter, enough fry survive on their own that a colony quietly maintains itself, though breeding is slower and fry losses higher than with the larger corys because everything is so small.

Common problems

The big one is group size: in a group smaller than six the pygmy cory is shy, pale, and hidden, and the fix is simply to keep more, since natural midwater schooling only appears in a decent crowd. Their tiny body mass leaves little buffer against poor water, so they are more sensitive to swings than larger corys and need stable, clean conditions. Ich during acclimation is best handled with raised temperature rather than full-strength medication on such a small fish, and wild-caught stock can carry internal parasites that cause wasting. A fine sand bottom protects the barbels they feed with, and with only a few years of life a colony has to breed to keep going.

Bioload

Further reading

• Keeping shrimp with fish: what actually works
• Stocking ideas by tank size