Pygmy Corydoras (Gastrodermus pygmaeus)

Pygmy Corydoras are tiny, peaceful armoured catfish best kept as a proper social group in a mature planted aquarium. The currently accepted scientific name is Gastrodermus pygmaeus; aquarists and suppliers still widely use the former combination Corydoras pygmaeus. This Shopify product combines two supplier size listings under one parent product: choose either 1-2 cm or 2-2.5 cm when that variant is available.

What one quantity buys: one unsexed fish in the selected size band. The size is an approximate dispatch band, not a promise of age, sex or exact adult colour. This is a shoaling species rather than a fish to keep alone, so plan a group of at least eight, with ten to twelve preferred when the aquarium footprint and filtration can support them.

The supplier describes these variants as “Corydoras pygmaeus black”. “Black” is a supplier trade descriptor, not a formally recognised taxon or a guarantee that every fish will be uniformly black. Typical G. pygmaeus are slim, silvery fish with a dark horizontal stripe. The current gallery image is a representative dark Corydoras scene, not a photograph of the exact fish or current batch; use the verified identity, dispatch-size selector and batch information above when deciding whether this listing suits your aquarium.

Quick Reference

Identity, Taxonomy and the Supplier “Black” Label

The fish long known in the aquarium trade as Corydoras pygmaeus was moved to the reinstated genus Gastrodermus in the 2024 revision of the Corydoradinae. Eschmeyer’s Catalog of Fishes now treats Gastrodermus pygmaeus (Knaack, 1966) as the valid name. The older name remains useful because it is still printed on supplier lists, care guides and product searches. Both names on this page refer to the same species; the taxonomy bridge is included to help customers compare older and current sources without mistaking them for two different fish.

Petra Aqua’s source listings call both size variants “Corydoras pygmaeus black”. No authoritative taxonomic source reviewed for this listing recognises “black” as a subspecies or separate accepted form. It may be a trade or batch descriptor, so it should not be used to promise a stable colour morph. Standard Pygmy Corydoras have a silvery to grey body with a narrow dark stripe along the side and a second finer lower line. Stress, age, lighting, substrate and the individual fish can all affect how dark the body looks.

This distinction matters because several other Corydoras-type fish are sold with “black” in a common name. A Black Venezuela Cory, for example, is a different, larger trade fish and should not be treated as a Pygmy Corydoras. The accepted species identity and the current supplier record anchor this listing; the representative gallery image alone must not be used for species identification.

Is a Pygmy Corydoras Right for Your Aquarium?

This species suits an aquarist who can provide a mature aquarium, a same-species group, gentle tank mates and deliberate feeding. It is often described as a nano fish because of its adult size, but “nano” should not be read as “suitable for any tiny container”. A group needs usable horizontal space, clean water, cover and enough open area to move between the lower and middle levels.

Pygmy Corydoras are not algae eaters and should not be bought as a clean-up solution. They forage over sand and may consume small edible particles that reach the bottom, but they still require complete food of their own. They can starve in a busy community even while other fish appear well fed. Their small size also makes sudden water-quality changes and aggressive companions more consequential than they would be for a larger Corydoras.

Adult Size, Shape and Normal Appearance

FishBase records a maximum of about 2.1 cm standard length for male or unsexed G. pygmaeus. Standard length excludes the tail fin, which is why aquarium descriptions that use total length often quote a figure closer to 2.5 cm. Mature females are generally fuller through the abdomen and may look larger than males, but juveniles in the two dispatch bands cannot be reliably sexed from a product selector.

A normal Pygmy Corydoras is more slender than many familiar Corydoras species. The body is silver-grey with a strong dark lateral stripe that runs from the snout towards the tail and usually broadens near the caudal peduncle. The small barbels around the mouth are used to investigate the substrate. Healthy fish should have intact barbels, clear eyes, fins held normally and enough body condition that the abdomen does not look pinched.

Colour in a shop, bag or newly introduced aquarium may be paler or darker than settled colour. Transport stress can suppress normal contrast. A dark substrate and shaded planting can make the stripe look more pronounced, but they do not turn the species into a uniform black morph. Ask for current batch confirmation when exact colour is important to your purchase; no representative image can guarantee the appearance of an individual live animal.

Natural Distribution and Habitat

Gastrodermus pygmaeus is a South American freshwater catfish associated with the Amazon basin. The original type locality is near Calama on the Rio Madeira system in Rondônia, Brazil, and current catalogue records cover a wider Amazonian distribution. FishBase also identifies the Madeira River basin and describes the species as tropical freshwater fish.

For aquarium planning, the useful habitat lessons are more important than trying to reproduce one exact riverbank. These fish benefit from a soft, clean bottom, plant cover, submerged wood or roots, quieter areas away from a filter outlet and access to the surface. Corydoradine catfish can take atmospheric air, so the surface should remain unobstructed and the aquarium should have a secure cover with a sensible air gap.

Leaf litter can add shelter and natural foraging surfaces, but use aquarium-safe leaves and remove material that is fouling the water. Plants such as Java fern, Anubias, Cryptocoryne, mosses and fine-leaved stems provide resting places without taking away all open swimming room. Floating plants can soften bright light, although dense surface cover should not prevent the fish reaching air.

Tank Size and Group Planning

A practical starting point is an aquarium of about 45 litres with a useful horizontal footprint. A ten-US-gallon tank is often cited by experienced specialist keepers for a group, but litres alone do not describe shape, stocking or filtration. A longer 45-litre aquarium offers more usable movement and feeding area than a tall tank of the same volume. Larger water volume also slows changes in temperature and chemistry.

Keep at least eight Pygmy Corydoras together. Ten to twelve usually gives a better chance of seeing confident social behaviour, provided the tank is not overstocked. A group does not need to move as a tight school every minute. Individuals may rest on leaves or hardscape, forage across the bottom and then gather or hover together in the lower mid-water. Persistent hiding can indicate an undersized group, bright exposed surroundings, unsuitable tank mates or poor water conditions.

Calculate the final group before ordering. If you already have this species, add enough fish to create a suitable group after allowing for the tank’s total bioload. Different Corydoras species do not replace same-species companions: they may associate, but a mixed collection of single fish is not equivalent to eight Pygmy Corydoras. For broader setup guidance, read the Corydoras care guide and the dedicated Pygmy Corydoras UK guide.

Water Parameters and Stability

Maintain 22-26°C. FishBase gives a broad species range of pH 6.0-8.0 and hardness of 2-25 dH, while long-term aquarium references usually recommend a narrower, softer range. For routine home care, pH around 6.0-7.5 and roughly 2-15 dGH provide a cautious working window. Stability, acclimation and water cleanliness matter more than chasing a single “perfect” number inside that range.

Ammonia and nitrite should remain at zero in a cycled aquarium. Keep nitrate controlled through sensible stocking, feeding and regular partial water changes. Test the aquarium before adding fish and whenever behaviour changes. A small catfish can show stress quickly if a filter is immature, food is decomposing in the substrate or a large water change introduces a sharp temperature or chemistry difference.

Do not use the group to cycle a new aquarium. Establish the biological filter first and allow the tank to become stable. Acclimate new fish to the destination water rather than trying to alter the aquarium suddenly to match a bag reading. If your tap water sits outside the working range, plan any adjustment with a repeatable method and suitable test equipment; unstable correction can be worse than a consistent value near an acceptable boundary.

Filtration, Flow and Oxygen

Choose filtration that can process the aquarium’s waste without pinning these small fish against the current. A mature sponge filter, a correctly sized internal filter with a diffused outlet, or a canister return broken up by a spray bar can all work. Keep intake gaps safe for small fish. Flow should leave calmer feeding and resting zones while still circulating oxygenated water around the aquarium.

Warm water holds less oxygen, so surface movement and sensible stocking remain important, especially near the top of the temperature range. Rapid breathing, repeated distressed dashes to the surface or the whole group crowding one high-flow area should prompt immediate checks of temperature, oxygen, ammonia and nitrite. Occasional air-gulping is a normal Corydoradinae behaviour; repeated emergency-looking surfacing is not something to dismiss.

Substrate, Plants and Layout

Fine, smooth sand is the clearest substrate choice because it supports natural foraging and is gentle around the mouth and barbels. Rounded fine gravel can be workable when it is genuinely smooth and kept clean, but sharp or coarse material increases abrasion risk and traps food where these fish feed. Substrate hygiene and water quality are at least as important as the material name.

Leave open feeding patches between planted areas. Dense planting around the sides and back can create security, while open foreground sand lets the group search for food and lets you observe body condition. Wood, leaf litter and low caves can break sight lines, but do not create narrow traps that are difficult to inspect. Keep decorations stable so burrowing or maintenance cannot cause a collapse.

Moderate lighting is suitable when plants or hardscape create shade. A bare tank under intense light may leave the group exposed and reluctant to feed in the open. A regular day-night cycle is more useful than an arbitrary long lighting period. Set lighting around plant needs and algae control, then provide shaded resting areas within that plan.

Feeding: Small Food, Delivered Deliberately

Pygmy Corydoras are small omnivorous foragers that need animal-rich and mixed foods in particles they can swallow. Use a quality micro sinking pellet, soft sinking granule or finely crushed complete food as a staple. Add appropriately sized frozen or live foods such as daphnia, cyclops, baby brine shrimp or microworms. Bloodworm can be too large unless finely cut, and it should be a varied-food component rather than the whole diet.

They are not algae eaters. They may investigate biofilm and edible particles, but algae wafers intended for herbivorous grazers are not a complete answer for this species. They are also not a substitute for gravel cleaning. Uneaten food and waste must still be removed during maintenance; adding bottom fish does not make that material disappear.

How to Make Sure the Group Eats

Watch the food reach the fish. In a community aquarium, feed fast mid-water species first and place small sinking food in more than one lower area. Feeding after the brightest lights dim can reduce competition, but you should still be able to inspect the group. A rounded, well-fed abdomen is useful; a pinched belly, falling body condition or repeated retreat from food indicates a problem even if pellets remain somewhere in the tank.

Offer one or two small meals daily and adjust the amount to the group, temperature and tank community. A rigid “finish in two minutes” rule can be misleading for shy bottom fish because food may take time to reach them. The better test is whether each fish gets access while little or no food remains to decay. Remove excess and review portion size rather than compensating with a very large next meal.

Behaviour and Social Life

Pygmy Corydoras differ from many larger corys because they regularly use the lower mid-water as well as the substrate. A settled group may hover together, dart between plants, pause on broad leaves and return to the sand to forage. That activity is normal and is one reason the species is more visible than its small size suggests.

They remain peaceful and do not defend a territory. Peaceful does not mean invulnerable: a fish only a few centimetres long can be eaten, intimidated or denied food by tank mates that would coexist with a larger Corydoras. Choose companions by adult size, feeding speed and behaviour, not only by whether a care chart labels them “community fish”.

Allow new arrivals time to settle. A recently transported group may hide, rest low or show reduced colour. Dim lighting, stable water and small familiar foods help. Escalate concern when fish remain isolated, cannot hold position, breathe rapidly, clamp fins, show white spots or lose body condition.

Compatible and Incompatible Tank Mates

Suitable companions are small, calm fish that share the temperature range and do not monopolise food. Tiny rasboras, ember-sized tetras, peaceful small danios and Otocinclus can work in a well-sized, mature setup. Adult dwarf shrimp are often ignored, but no fish listing should guarantee the safety of every shrimp juvenile or newly moulted individual.

Use caution with bettas and dwarf gouramis because individual temperament varies. Avoid large cichlids, predatory catfish, boisterous barbs and any fish capable of swallowing or repeatedly chasing a Pygmy Corydoras. Larger Corydoras are peaceful but can be stronger feeders; they do not replace the same-species group and need more floor space.

For other correctly routed Corydoras listings, compare the False-Spotted Cory and Rio Napo Cory. These are different species with different adult sizes; links are for comparison, not a suggestion to substitute mixed single fish for a Pygmy Corydoras group. The wider Corydoras category provides additional options.

Acclimation and the First Week

Prepare the aquarium before the delivery arrives: confirm temperature, ammonia, nitrite and the destination tank mates. Follow the acclimation instructions supplied with the order, keep lights low and avoid adding transport water unnecessarily. Do not extend acclimation indefinitely once a bag has been opened; changing oxygen and pH can alter ammonia toxicity.

Offer a small meal only after the fish have had time to settle, and make sure food is appropriately sized. Count the group during quiet periods, inspect breathing and check that no individual is being excluded. It is normal for a new group to be cautious, but persistent rapid breathing, inability to balance, obvious injury or failure to feed needs prompt attention.

Quarantine is the safest way to protect an established aquarium when appropriate facilities are available. A quarantine setup must itself be cycled, heated, covered and suitable for a social group; a tiny uncycled container can create more risk than it prevents. Do not medicate prophylactically without a diagnosis. Corydoradine catfish and invertebrates can be sensitive to some products, so identify the condition and follow the current manufacturer directions for the exact medication.

Sexing and Breeding

Adults are easiest to compare from above. Females are usually broader and fuller through the abdomen, while males tend to remain slimmer. Dispatch-size juveniles cannot be reliably sexed, and this listing does not promise a male, female, pair or breeding group. Starting with a reasonably sized social group gives a better chance of both sexes without turning that chance into a guarantee.

Spawning follows the characteristic Corydoradinae pattern. FishBase records the female holding two to four eggs between the pelvic fins while fertilisation takes place, then attaching the adhesive eggs to a chosen surface. A sequence can continue until many eggs have been deposited. Aquarium observations vary by condition and individual group, so an egg count should not be treated as a promise.

Well-conditioned adults may spawn after a cool water change, but breeding should never be triggered by a temperature shock outside the normal safe range. Use varied food, clean water and steady maintenance first. Eggs may be placed on glass, plants or equipment and can be lost to fungus or predation. Hatching time depends on temperature and condition; specialist aquarium guidance commonly reports about two to five days.

The fry are extremely small. They need clean, stable water and food that matches their mouth size, progressing from microscopic foods to microworms and newly hatched brine shrimp. Overfeeding can spoil the water faster than the fry can eat. A mature sponge filter and frequent observation are more useful than adding medication by routine.

Health, Welfare and Warning Signs

Healthy fish are responsive, maintain position normally, forage with the group and show intact barbels and fins. Brief resting is normal; persistent isolation, clamped fins, rapid breathing, flashing, white spots, redness, damaged barbels or a hollow abdomen are reasons to investigate. Start with water tests, temperature, oxygen and feeding access before assuming a disease.

Barbel damage is often associated with poor substrate hygiene, abrasion and deteriorating water conditions rather than sand or gravel as a label alone. Keep the bottom clean without stripping the aquarium of all mature biological surfaces. Use a siphon carefully around plants and avoid letting fine food accumulate out of sight.

Do not raise temperature or dose salt, copper or any other medicine as a generic response. Some treatments that are appropriate for one diagnosis are harmful or ineffective for another, and copper is dangerous to many invertebrates. Isolate affected fish when that can be done in a stable suitable system, seek an informed diagnosis and follow the product label. Increase aeration when illness, heat or medication could reduce available oxygen.

A fixed lifespan is not promised. Longevity depends on origin, age at purchase, genetics, water quality, nutrition, social conditions and disease history. The practical goal is to remove preventable stress: keep a real group, provide enough space, feed each fish, maintain stable water and choose companions that cannot intimidate them.

Pygmy Corydoras Compared with Other Small Corys

G. pygmaeus is sometimes confused with other dwarf species. The Salt-and-Pepper Cory formerly known as Corydoras habrosus has a deeper body with broken blotches, while the Tail-Spot Cory formerly known as Corydoras hastatus carries a prominent spot near the tail. Pygmy Corydoras are recognised by their slimmer shape and continuous dark side stripe.

These species also differ in how visibly they use mid-water. Pygmy and Tail-Spot Corys are particularly associated with hovering or schooling above the substrate, whereas Salt-and-Pepper Corys spend more time in the lower zone. All remain social fish requiring same-species companions. Do not mix a few of each merely to reach a group count.

Standard-sized Corydoras such as Sterbai, Peppered or many spotted forms require more floor space and usually create more feeding competition. They can be excellent fish in the right aquarium, but their peaceful temperament does not make their space needs interchangeable with this species. Compare adult size, temperature and group footprint before choosing.

Frequently Asked Questions

Is the current scientific name Corydoras pygmaeus or Gastrodermus pygmaeus?

Gastrodermus pygmaeus is the current accepted combination in Eschmeyer’s Catalog of Fishes following the 2024 Corydoradinae revision. Corydoras pygmaeus is the former name and remains the most familiar supplier and search term, so both are shown clearly.

Does “black” mean this is a recognised black morph?

No formal black subspecies or taxon was verified. “Black” is retained as the supplier’s descriptor only. Typical Pygmy Corydoras are silver-grey with a dark lateral stripe, and exact batch colour should be confirmed rather than inferred from the representative image.

How many fish does one quantity buy?

One quantity buys one unsexed fish in the selected size band. The two Shopify options are sizes, not pack counts. Plan and order a suitable same-species group rather than assuming one line item contains a pair.

How many should live together?

Keep at least eight, with ten to twelve preferred where aquarium space, filtration and total stocking allow. A group makes normal social behaviour more likely and reduces the insecurity commonly seen in isolated fish.

Can they live in a 30-litre nano tank?

A very experienced keeper may manage a small group in a carefully designed small tank, but about 45 litres with a useful horizontal footprint is a safer general recommendation. It provides more swimming area and a larger buffer against rapid water-quality changes.

Do Pygmy Corydoras clean algae?

No. They forage around the lower aquarium but are not algae-eating fish. Feed a complete small sinking food and suitable frozen or live foods; do not expect them to live on algae or leftovers.

Are they easy community fish?

They are peaceful but not automatically easy in every community. Their small size makes them vulnerable to predation, intimidation and food competition. A mature planted aquarium with tiny calm companions is a better match than a busy general community.

Can I keep them with shrimp?

Adult peaceful shrimp are often compatible, but no fish can be guaranteed safe with every tiny shrimplet. Make sure both groups receive suitable food and that water parameters work for all inhabitants.

Do they need sand?

Fine smooth sand is preferred because it supports natural foraging and is easy on the barbels. A genuinely smooth fine gravel can work when kept clean, but sharp or dirty substrate is unsuitable.

Can the dispatch size identify the sex?

No. The 1-2 cm and 2-2.5 cm options describe approximate size, not sex. Adult females tend to be fuller than males, but this listing supplies unsexed fish.

Ordering, Delivery and Evidence Limits

Choose the size variant shown as available and set the quantity needed for your planned group. Stock, price and dispatch options are live commerce data and can change, so they are intentionally not hard-coded into this care text. Review the current delivery and Live Arrival Guarantee page before ordering livestock.

The taxonomy in this listing follows Eschmeyer’s Catalog of Fishes, while species size, distribution and broad environmental data are checked against FishBase. Practical aquarium recommendations are intentionally narrower and more cautious than a full biological tolerance range. They draw on established specialist husbandry references and are presented as planning guidance, not as proof that every value inside a range will suit every aquarium.

Live fish vary. Exact sex, shade, stripe contrast, adult size, behaviour and breeding potential are not guaranteed. The gallery is representative and the supplier’s “black” wording remains an explicitly limited trade descriptor. The most reliable buying decision comes from matching the verified species, social needs, size option and care requirements to a stable aquarium rather than choosing solely from a generated image or colour label.