Nijssen's Corydoras
Corydoras nijsseni
A stunning blackwater catfish from the Rio Negro. Its pale armored body exhibits large dark plates and subtle yellowish pectoral fins. It mandates dimly lit, tannin-rich biotope tanks.
Water Temperature
22 - 26 °C
pH Value
6 - 7.2
Water type
Freshwater
Tank level
Bottom
Adult size
5 cm
Minimum tank volume
>= 80 L
Minimum group
>= 6
GH
2 - 12 dGH
KH
1 - 8 dKH
TDS
40 - 260 ppm
Conductivity
63 - 406 uS/cm
Species description
Geographical Origin and Habitat: Endemic rarity of the Ucayali River basin, in central-eastern Peru. Resides in small forest streams characterized by dark or amber waters, thickly shaded by lush vegetation and covered by intricate root tangles.
Taxonomy and Morphology: Species discovered in honor of the ichthyologist Han Nijssen. Member of the "short-snouted" Callichthyidae. Reaches 5 cm (2 inches); its appearance is extremely round, compact, and graceful compared to other variants of the genus.
Social Behavior: Essence of tranquility. Strictly needs conspecific interaction: inserted in schools of over 8 individuals, it will confidently inspect the bends of the tank with rhythmic and harmless liveliness.
Coloration and Sexual Dimorphism: Distinguished by three huge dark "saddle" spots: a deep orbital mask, a majestic black block under the dorsal fin, and a third saddle along the caudal peduncle, on a pale cream background. Bellies of females visibly swollen if gravid.
Care, breeding and tankmates
Aquarium Setup: Requires dark setups, preferably "blackwater" biotopes: fine and non-reflective silica sand, thick leaf deposits (Catappa), and hut-like woody roots. Hates bright lights, mitigated with floating flora.
Diet and Feeding: Eminently predator of micro-zoobenthos. Often shuns classic flakes: feed regularly with sinking foods for bottom fish with a very high protein level, mixed with bloodworms, white worms, and live or frozen daphnia.
Water Quality: Optimal maintenance at 22-26°C (72-79°F). Recommended medium/soft hardnesses (GH 2-12). pH between 6.0 and 7.2. Suffers dramatically from the accumulation of putrefied bacterial debris in the substrate: frequent changes and light water siphonings are necessary.
Compatibility and Cohabitation: The roommate par excellence for tiny South American rasboras (Nannostomus, Boraras) or small Apistogramma. Strictly eclipse the presence of intrusive territorial fish or any larger predator that could swallow it.
Aquarium Breeding: Considerable challenge for the breeder: triggered by intense cold thermal shocks. Couples lay a few robust adhesive eggs individually on fine-leaved flora (Mosses). Marked tendency of the colony to devour its own brood.
Risks and Diseases: Irreparable and deadly loss of barbels if housed on rough inert quartz. It is ruthlessly sensitive to copper and does not tolerate shock treatments against classic mycoses. Avoid nocturnal oxygen drops.
Geographic Origin and Distribution
Endemic rarity of the Ucayali River basin, in central-eastern Peru. Resides in small forest streams characterized by dark or amber waters, thickly shaded by lush vegetation and covered by intricate root tangles.
Origin
Amazon, Orinoco, and Guianas
Fish profile
- Temperament
- Semi-aggressive
- These catfish are incredibly docile, peaceful, and non-aggressive, making Corydoras nijsseni perfect community tank residents. They are somewhat shy by nature and heavily rely on the presence of a school to feel secure and display their natural behaviors. Providing plenty of hiding spots such as caves, driftwood, and dense vegetation will make them feel more comfortable. They never bother other fish and often completely ignore species occupying the middle and upper levels of the tank.
- Diet
- Omnivore
- Corydoras nijsseni is an omnivorous bottom feeder that constantly scavenges for food in the substrate. Their diet should be primarily composed of high-quality sinking pellets or wafers specifically formulated for bottom dwellers. To ensure optimal health and coloration, supplement their dry food with live or frozen foods such as bloodworms, daphnia, and brine shrimp. They will also eat uneaten food that falls from the surface, though they should not be treated merely as a clean-up crew.
- Life expectancy
- 5-10 years
- This species usually lives between 5 and 10 years when housed in a well-managed and stable aquarium. Water quality plays a crucial role, particularly the constant monitoring of nitrates and phosphates. Using a non-sharp substrate is essential to prevent injuries to the barbels that could lead to fatal infections. Providing a balanced diet contributes significantly to ensuring a long and healthy life for this fish.
- Adult size
- 5 cm
- The catalog's scalar value is 5 cm. The FishBase SPECIES table (v25.04 snapshot) source reports a maximum adult measurement of 3 cm for this species, recorded as standard length (SL). The taxonomic record consulted is Corydoras nijsseni (v25.04); male or unsexed record. These figures are not interchangeable: the first is the profile's editorial reference, whereas the second is a published maximum under a specific measurement convention; differences among sources can reflect sex, population, life stage and measuring method.
- Sex ratio
- School
- While sexing them can be challenging, a ratio of two or three males per female is generally recommended for breeding Corydoras nijsseni. Females are noticeably rounder and broader, especially when viewed from above, and tend to grow slightly larger. Males appear more slender and streamlined in comparison. Keeping them in a mixed-sex school naturally accommodates these ratios without requiring precise selection by the aquarist.
- Feeding frequency
- Twice daily
- These active scavengers should be fed one to two times daily to ensure they receive adequate nutrition. It is important to offer Corydoras nijsseni only as much food as they can consume within a few minutes to prevent water quality issues. Since they are somewhat nocturnal by nature, feeding them once right before the aquarium lights turn off can be very beneficial. Monitoring their feeding is essential, especially in community tanks where faster mid-water fish might outcompete them for food.
- Bioload
- Corydoras nijsseni has a relatively small bioload compared to larger aquarium fish. Due to their compact size, they produce a manageable amount of waste that standard filtration can easily process. However, because they must be kept in groups of at least six, the cumulative bioload should be considered when stocking. Regular water changes and good mechanical filtration are still necessary to keep the substrate clean where they dwell.
- Flow
- Stagnant
- In the wild, Corydoras nijsseni typically inhabits slow to moderately flowing streams and tributaries. They appreciate some gentle water movement in the aquarium, which helps keep the water well-oxygenated. However, excessive current or strong powerheads should be avoided as it can exhaust them over time. A standard sponge filter or a hang-on-back filter with baffled flow usually provides the ideal water dynamics for this species.
- Reproduction
- Oviparous
- Breeding Corydoras nijsseni in captivity is achievable but requires specific conditions to trigger spawning. A common trigger involves performing a large, slightly cooler water change to simulate the onset of the rainy season in their natural habitat. Females will lay adhesive eggs on broad-leaved plants, aquarium glass, or other flat surfaces. Once spawning is complete, the adult fish should be removed or the eggs transferred, as they may exhibit egg-eating behavior.
- Compatibility & tankmates
- This species is highly peaceful and makes an excellent addition to community aquariums. Corydoras nijsseni gets along perfectly with small tetras, rasboras, dwarf cichlids, and peaceful livebearers. It is crucial to avoid housing them with large, aggressive, or predatory fish that could bully them or attempt to eat them. As a schooling fish, they find safety and comfort in numbers of their own kind or similar Corydoras species.
- Tank level
- Bottom
- As classic bottom dwellers, Corydoras nijsseni occupies the lowest levels of the aquarium. They spend their days tirelessly exploring the substrate in search of morsels of food using their sensitive barbels. It is absolutely essential to provide a soft, sandy substrate to prevent damage to their delicate sensory barbels. Although they mostly remain at the bottom, they will occasionally dart to the water surface to swallow a bubble of air for intestinal respiration.
Scientific Parameters & Models
FishBase
Window to the official scientific data of the species
Data synced on: 06/15/2026
- Trophic level
- 3 ± 0.3 se
- Resilience
- High (less than 15 months)
- Phylogenetic uniqueness (PD50)
- 0.5001
- Bayesian Length-Weight
- a = 0.00741, b = 3.14
- VulnerabilityLow vulnerability (10 / 100)
Image gallery
Licensed images linked to the species or, when marked, to the closest representative taxon.
Related species
Recommendations grouped by close relatives, companion choices, and similar care.
