Pygmy cory

Quick facts

Adult size

2.5 cm

Lifespan

can live up to 5 years

Tank zone

all

Temperament

peaceful

Difficulty

beginner

Schooling

recommended 8+ (critical minimum 6, thrives at 12+)

Water parameters

Temperature

22–26°C

pH

6.0 to 7.5

Hardness

1 to 12 dGH

Tank requirements

Minimum volume

38 L

Minimum length

45 cm

Flow

low

Lighting

dim preferred

Substrate

sand

Driftwood

preferred

Hiding spots

needed

Feeding

Diet: omnivore, feeds primarily at the all.

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.

Habitat

Native to the Madeira River basin in Brazil, a major Amazon tributary. Found in slow-moving streams and flooded forest margins over leaf litter and fine sand. Unlike most Corydoras that are strict bottom-dwellers, pygmy corys (Corydoras pygmaeus) spend a significant portion of their time hovering in the midwater column, sometimes quite high in the water. They rest on broad leaves, wood surfaces, and even the glass, not just the substrate floor. This midwater behavior makes them more visible than typical bottom-dwelling corys. Adult size is tiny: 2–3 cm at maturity. Males are slimmer; females are rounder when viewed from above. The body is pale with a thin dark horizontal stripe running from snout to tail base. Not flashy, but in a big group against a planted background, the synchronized hovering and darting is captivating. Commercially bred but also frequently wild-caught. Both forms are inexpensive and widely available.

Breeding

Spawns in aquariums with the same water-change trigger as other Corydoras. Cool water change (drop 3–4°C), high-protein diet conditioning for a week, and a mature group of 10+. Eggs are deposited individually on plant leaves, glass, and decor; each egg is placed in the T-position and stuck to a surface. Clutch sizes are small (10-30 eggs) compared to larger corys. Eggs hatch in 3-4 days. Fry are extremely tiny and need infusoria or paramecium for the first week before graduating to baby brine shrimp. In densely planted tanks with moss and leaf litter, fry survive without intervention because there are enough microorganisms to sustain them and enough hiding spots to avoid being eaten. A stable colony in a planted nano tank self-maintains through continual low-level breeding. The species breeds more slowly than bronze or peppered corys, and fry mortality is higher because of their tiny size.

Common problems

Stress in small groups is the main issue. Pygmy corys kept in groups under 6 are shy, pale, and spend most of their time hidden in plant cover. The solution is simple: buy more. They're cheap. Ich is a risk during acclimation and transport stress; treat with temperature elevation (29–30°C for 3 days) rather than medication, as their small body mass makes chemical treatments riskier. Internal parasites from wild-caught specimens cause wasting; treat with levamisole. The species is more sensitive to poor water quality than larger corys because the small body provides less buffer against parameter swings. Keep nitrate below 20 ppm. Short lifespan (3-4 years) means the colony needs to breed to sustain itself if you want a long-term population.

Bioload

Bioload coefficient: 0.4 (very small cory; load comparable to a medium tetra).

Bioload coefficients are calibrated against the neon tetra as the anchor (1.0). See the methodology page for the formula and how each value was derived.

Further reading

• Stocking ideas by tank size