By James Okafor
A cory that doesn't act like a cory
You came here for a cory catfish, and you're picturing the usual thing — a stout little fish trundling along the gravel, hoovering up leftovers. Put that picture aside. The pygmy corydoras is the one member of the genus that breaks the rules: it spends most of its day hovering in mid-water, in a loose, drifting shoal, behaving far more like a tetra than a bottom-dweller.
I'm James, the aquascaper on the Tropical Fish Co team — planted nano tanks are my whole world, and the pygmy cory is the fish I reach for more than almost any other when I want movement at every level of a small aquascape. This page is the answer I'd give a customer who walks in and asks, "I want a cory for my little planted tank — which one, and how many?" The honest version, grounded in our own tanks, FishBase, Seriously Fish and a proper UK biotope feature — not the recycled care-sheet you've already read five times.
The pygmy (Corydoras pygmaeus, recently reclassified as Gastrodermus pygmaeus [4]) tops out at around 2.1–2.5 cm [1] — the smallest cory in the UK trade. That tiny size, the mid-water habit, and a completely shrimp-safe temperament make it a different proposition from the bronze and panda corys on our corydoras buying guide. If you've got a 30–60 litre planted tank, this is arguably the cory for you.
Pygmy corydoras hang in open mid-water rather than resting on the substrate — stock and plant the tank with that in mind. Photo: Tropical Fish Co.
Fun facts — what most UK guides skip
- It swims in mid-water — almost alone in its genus. Seriously Fish puts it perfectly: "Unlike the majority of its congeners it has a charming habit of swimming in midwater" [3]. A UK biotope feature notes they rest on broad plant leaves well away from the substrate and rise higher in the water to feed at dawn and dusk [5]. Most corys never leave the floor.
- It breathes air through its gut. Like other Corydoras, the pygmy is a facultative air-breather [1] — a peer-reviewed histology study confirmed the hind part of the intestine works as an accessory breathing organ, with the fish taking in air during a rapid dash to the surface [2]. That occasional dart upward isn't stress; it's respiration.
- A 2.5 cm fish from three river basins. The species is spread across the Madeira (Brazil), Nanay (Peru) and Aguarico (Ecuador) drainages [1], in soft, warm lowland water — which is exactly the chemistry to aim for at home.
- Females are the bigger sex. In a mature shoal the females run slightly longer and noticeably rounder than the slimmer males — the easiest way to spot a breeding-ready group before you ever see eggs.
- It shoals, then loosens up to feed. During the day they hold a tight group; at dawn and dusk that cohesion relaxes as they spread up the water column to forage [5]. Watching the shoal "switch modes" is one of the quiet pleasures of keeping them.
Pygmy vs the other small corys — which is right for you?
Three "small corys" get sold for nano tanks, and people mix them up constantly. Here's how the pygmy compares — plus otocinclus, the other tiny algae-grazer keepers cross-shop it against.
| Attribute | Pygmy cory (C. pygmaeus) | Panda cory (C. panda) | Julii/leopard cory (C. julii) | Otocinclus |
|---|---|---|---|---|
| Adult size | 2.1–2.5 cm | 5 cm | 5.5 cm | 4 cm |
| Where it swims | Mid-water + bottom | Bottom | Bottom | Glass + plant surfaces |
| Min tank (shoal) | 30 L | 60 L | 60 L | 60 L |
| Group size | 8+ (10–15 ideal) | 6+ | 6+ | 6+ |
| Shrimp-safe | Yes | Yes | Yes | Yes |
| Main job | Mid-water movement | Bottom foraging | Bottom foraging | Soft green-algae grazing |
| Best for | Planted nano tanks | Standard community | Standard community | Algae control in planted tanks |
Want the genuine nano specialist that fills the empty middle of a small tank? Pygmy cory. Need a robust bottom-worker for a 60 L+ community, or specifically an algae-grazer? Look at the panda, julii or otocinclus instead.
Because it lives in mid-water, treat the pygmy cory as a feature shoal in its own right — like a tetra — not as a bottom cleaner you add on top of a full stocking list. Count it in your bioload and your visual plan for the middle of the tank, and plant accordingly with broad-leaved species it can rest against.
How many to buy — and why eight is the floor
This is the number that makes or breaks the fish. Pygmy cories are a shoaling species, and independent references are blunt about it: "best to buy at least 6, preferably 10 or more" [3]. In our own tanks the difference between six and twelve is night and day — a small group skulks in the planting, while a dozen-plus shoal hangs out in open water all day. Eight is the minimum I'd ever sell as a starter shoal; ten to fifteen is the target.
The good news is their size makes big numbers easy. At 2.5 cm, a shoal of 10–15 fits a 30–45 litre planted tank without straining the bioload — far less waste than a single fish ten times the volume. Footprint beats height: they cruise side to side, so a low, wide nano works far better than a tall cube.
Tank mates — small, peaceful, and shrimp-safe
A 2.5 cm fish needs 2.5 cm-friendly company. The rule is simple: match by adult size and temperament, not by the word "community" on a shop tank. Anything that treats a pygmy cory as a snack, or simply bustles it off its food, is wrong — even an otherwise-peaceful angelfish or full-size gourami is too much.
What works beautifully: small schooling tetras and rasboras for the upper water, peaceful algae-grazers, and the whole invert crew. Pygmy cories are completely shrimp-safe — their mouths are built for micro-food, so adult cherry and Amano shrimp share a tank with them in total peace.
Pygmy corydoras tank mate compatibility
| Tank mate | Verdict | Why |
|---|---|---|
| Ember tetra | ✅ Good | Tiny, peaceful upper-water shoaler |
| Neon & cardinal tetra | ✅ Good | Classic mid/upper community |
| Otocinclus | ✅ Good | Soft-algae grazer, similar care |
| Cherry & Amano shrimp | ✅ Good | Fully shrimp-safe |
| Nerite snails | ✅ Good | Algae control, no risk |
| Larger corys (60 L+) | ✅ Good | Panda, julii — bottom shoal in a bigger tank |
| Dwarf gourami | ⚠️ Risky | Can intimidate at feeding time in small tanks |
| Peaceful dwarf cichlids | ⚠️ Risky | Only in larger, well-planted tanks |
| Angelfish & full-size gouramis | ❌ Avoid | Too big — stress the shoal off food |
| Bettas (some individuals) | ❌ Avoid | Temperament-dependent; nippy ones hassle them |
| Large or boisterous barbs | ❌ Avoid | Out-compete a 2.5 cm fish entirely |
For the planted side of the build, our corydoras care guide covers substrate and feeding in depth, the otocinclus guide pairs the perfect algae-grazer, and the shrimp-keeping guide sets up the invert colony. If your nano grows into a bigger display, the bigger corys on our main corydoras page become an option for the floor.
Broad and fine-leaved plants give pygmy cories the mid-water resting spots they'd use in the wild. A densely planted nano shows off their shoaling best. Photo: Tropical Fish Co.
Feeding a fish with a 2 mm mouth
The pygmy cory's size changes how you feed it. A standard catfish wafer or a chunky sinking pellet is simply too big — these are micro-grazers, picking at tiny morsels off the sand and off plant leaves. They're omnivores, so the menu is broad, but the particle size is the thing most keepers get wrong.
What works in our tanks: micro sinking pellets and crushed flake as the staple, plus frozen and live micro-foods as the treat — baby brine shrimp, micro-worms, frozen daphnia and cyclops. Because they spend time in mid-water as well as on the bottom [3], feed in a way that lets food drift down through the column rather than only sinking to one spot.
Pygmy cories feed more keenly at dawn and dusk, when they move up the water column [5]. In a mixed community, faster mid-water fish snatch everything first — so feed a sinking micro-food after the lights dim, when the tetras have settled, and watch for rounded little bellies. A pygmy cory with a sunken belly is being out-competed, not starved by design.
Aquascaping the tank around them
This is the part I care about most. Because the pygmy is a mid-water fish that rests on leaves rather than just the floor, the planting is the habitat — not decoration around the edges. In its native rivers it associates with marginal and broad-leaved plants well off the substrate [5], and you can recreate that cheaply in a nano.
Build it like this:
- Fine sand base, kept open across the front so you can watch them sift — their natural foraging behaviour is half the appeal.
- Broad-leaved mid-ground plants (Anubias on wood, Cryptocoryne, larger-leaved stems) to give the shoal the off-bottom resting spots it actually uses.
- Fine-leaved and floating cover (Java moss, guppy grass, floating plants) to soften the light and give nervous new arrivals somewhere to feel safe — a shy shoal becomes a confident one far faster in a well-planted tank.
- Gentle flow. They like a little current but not a torrent; a sponge filter or a baffled nano filter is ideal and doubles as safe for any fry.
Most cory aquascapes optimise the floor and leave the middle to tetras. The pygmy flips that: research-grade and hobbyist observations agree it spends much of the day in midwater and only loosens its shoal to feed higher up at twilight [3][5]. So plant the middle third of the tank for them — that's where they live — and you'll see the shoal far more than keepers who treat them as bottom fish.
Water, sand and a UK reality check
Aim for soft to moderately hard water, 22–26 °C, pH 6.0–7.5, 2–15 dGH [1]. They're adaptable and will settle into harder water than that, but they show their best colour and breeding behaviour in soft, slightly acidic conditions.
Across much of the South-East and beyond, the tap supply is hard: Thames Water states plainly that "all the water in our region is hard" thanks to chalk and limestone geology [6]. Pygmy cories will live in it, but for soft-water biotope keeping (and reliable breeding) you may want to cut tap water with RO or run the tank over botanicals. Check your own postcode's hardness before deciding — it varies street to street.
Almost every pygmy-cory failure comes down to one of two things. One: too few fish — a group of three or four lives stressed and hidden, feeds poorly and fades. Two: a brand-new tank — pygmy cories are sensitive to the ammonia and nitrite of an uncycled system. Buy a shoal of 8+ in one go, and only add them once the tank has run stable at zero ammonia and nitrite for several weeks. Sharp gravel is the quiet third killer — use sand.
When your pygmy corydoras arrive
Pygmy cories are small and sensitive — they hold far less water in transit than a big fish, so their bag chemistry shifts faster. We pack and you acclimate with that in mind:
- Receive into a quiet, dim room. Float the sealed bag for 15–20 minutes to equalise temperature — no lights blazing overhead.
- Slow drip-acclimate for 30–45 minutes at one to two drops per second. Small, sensitive fish do badly with a fast splash into new water; the slow drip lets pH and hardness shift gently [7].
- Net the fish into the tank — never pour the bag water in. Their armour makes them tougher to net than a tetra, so use a soft, fine net and take your time.
- Lights off for a couple of hours afterwards, and don't feed for 24 hours. Let the whole shoal find its feet first.
- Add the whole shoal together. Pygmy cories settle far better arriving as a group than dribbled in a few at a time — the shoal is their security.
Ready for more?
Our corydoras care guide goes deep on substrate, feeding and breeding across the genus, and the otocinclus guide covers the perfect soft-algae grazer to pair in the same planted nano.
Comparing corys? The main corydoras buying guide sets the pygmy alongside its bigger bottom-dwelling cousins, and the kuhli loach guide covers another small, peaceful, sand-loving oddball for the lower tank.
Browse the full range in the corydoras hub and the wider catfish & plecos hub.
