Natural-history-style illustration of the CW049 Black Diamond Cory (Hoplisoma sp. (CW049)).

Field Guide

CW049 Black Diamond Cory

Hoplisoma sp. (CW049)

Quick summary

The CW049 Black Diamond Cory is a peaceful, bottom-dwelling catfish with striking dark coloration that makes it a standout addition to community tanks. If you enjoy keeping shoaling corydoras and can provide soft, clean water with a sandy substrate, this relatively uncommon species is a rewarding choice for intermediate fishkeepers.

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Introduction

The CW049 Black Diamond Cory is one of those fish that stops you in your tracks at the shop. Carrying the CW (Corydoras World) number 049, it has not yet received a formal scientific description, so it currently sits under the genus Hoplisoma (formerly grouped within the broader Corydoras complex). Its common name comes from the deep, dark body peppered with a subtle sparkle that, under good lighting, genuinely looks like crushed black diamond. For hobbyists who have kept the more common bronze or peppered corydoras and want something a bit different, this fish delivers a real visual upgrade without demanding drastically different care.

People are drawn to the CW049 for a few reasons. First, the colour. It is darker and more dramatic than most corydoras species available in the trade, and it holds that colour well in a properly set-up tank. Second, it has the same endearing personality that makes all corydoras so popular: the shuffling, whisker-twitching search for food along the substrate, the sudden bursts to the surface for a gulp of air, and the way a group of them will pile on top of each other at rest. They are genuinely fun to watch, and they bring constant activity to the lower reaches of the aquarium.

That said, the CW049 is not quite as bulletproof as a bronze cory. It prefers softer, slightly acidic water and can be a little more sensitive to poor water quality. For that reason, it is best suited to fishkeepers who have some experience maintaining stable water parameters and who are willing to keep up with regular water changes. If you have successfully kept other corydoras or similarly sensitive South American species, you will find the CW049 Black Diamond a comfortable next step and a gorgeous one at that.

Quick stats

Scientific name Hoplisoma sp. (CW049)
Family Callichthyidae
Origin Brazil, Rio Negro basin tributaries
Adult size 5 – 6 cm
Lifespan 5 – 8 years
Difficulty Intermediate
Breeding difficulty Moderate
Temperature 23 – 27 °C
pH range 5.5 – 7.0
Minimum tank size 80 litres

Appearance

The CW049 Black Diamond Cory has a compact, rounded body typical of the Hoplisoma lineage. Its base colour ranges from deep charcoal grey to near-black, overlaid with a scattering of tiny iridescent spots that flash silver or gold when light catches them, giving the fish its “diamond” nickname. The dorsal fin often carries a pale leading ray that creates a neat contrast against the dark body. Pectoral and ventral fins are generally translucent with a faint smoky tinge, and the caudal fin may show faint lighter banding. The eyes are large and expressive, typical of corydoras, and the barbels are well developed, pale in colour, and constantly in motion as the fish explores.

Telling males from females is tricky with juveniles, but becomes easier as the fish mature. Females tend to be slightly larger and noticeably rounder when viewed from above, especially when carrying eggs. Males are typically a touch slimmer and may appear slightly more elongated. Both sexes share the same dark colouration, so you cannot reliably sex them by colour alone. In a well-fed group, the difference in body shape becomes the most reliable visual cue.

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Natural habitat

The CW049 Black Diamond Cory originates from tributaries of the Rio Negro basin in Brazil, one of the world’s great blackwater river systems. These waterways are stained dark brown by tannins leaching from decaying leaves and wood on the forest floor. The water is characteristically soft, acidic, and mineral-poor, with pH values often dropping below 6.0 in the dry season. The substrate in these streams consists of fine sand mixed with leaf litter, fallen branches, and submerged root tangles from overhanging vegetation.

Understanding this habitat matters because it directly informs how you should set up the aquarium. The soft, sandy bottom protects the fish’s sensitive barbels, while the leaf litter and wood provide shelter and maintain the low pH the species is accustomed to. Lighting in these forest streams is typically subdued, filtered through the canopy above. Replicating even some of these conditions, soft substrate, tannin-stained water, gentle flow, and dim lighting, will help the CW049 feel secure and display its best colouration.

Tank size and setup

A group of six CW049 Black Diamond Corys needs a minimum of 80 litres, with an additional 10 litres per extra fish beyond that. Because corydoras spend most of their time on the bottom, floor space matters more than height. A tank with a generous footprint, such as a standard 80 x 35 cm base, is ideal. Longer tanks are always preferable to tall, narrow ones for bottom dwellers.

Substrate is the single most important setup decision for this species. Use fine, smooth sand, something like CaribSea Super Naturals or JBL Sansibar. Avoid sharp gravel or coarse substrates that can damage their barbels and lead to bacterial infections. A thin layer of dried Indian almond leaves (Terminalia catappa) or oak leaves scattered across the sand replicates their natural environment and releases beneficial tannins that soften the water.

For decoration, include pieces of driftwood such as Malaysian bogwood or spider wood to create shaded resting spots. Add a few smooth river stones or coconut shell caves for additional cover. Planting is welcome and helps diffuse light. Choose species that tolerate soft, acidic water: Java fern (Microsorum pteropus), Anubias barteri var. nana, and various Cryptocoryne species such as Cryptocoryne wendtii all work well. Floating plants like Amazon frogbit (Limnobium laevigatum) or red root floaters (Phyllanthus fluitans) will dim the lighting naturally and make the fish feel more comfortable. Aim for moderate to low lighting overall. If you use an adjustable LED, turn it down or shorten the photoperiod to around 8 hours.

Water flow should be gentle to moderate. These fish come from slow-moving tributaries, not rapids, so a strong current will stress them. Position the filter outlet so it creates a mild circulation without blasting across the substrate.

Water parameters

Temperature 23 – 27 °C
pH 5.5 – 7.0
General hardness (GH) 2 – 10 dGH
Ammonia 0 ppm
Nitrite 0 ppm
Nitrate Below 20 ppm

The CW049 thrives in soft, slightly acidic water. If your tap water is naturally hard and alkaline, you may need to cut it with RO (reverse osmosis) water or use a remineraliser designed for soft-water setups. Stability matters more than hitting a perfect number, so avoid chasing an exact pH and focus instead on keeping parameters steady. Weekly water changes of 20 to 30 percent are a sensible baseline, and you should always match the temperature and approximate chemistry of the replacement water to what is already in the tank. Test your water regularly, especially in the first few months after setting up a new aquarium.

Filtration and equipment

A sponge filter or a small internal canister filter works well for tanks in the 80 to 120 litre range. If you prefer an external canister, models like the Eheim Classic 250 or the Oase BioMaster Thermo 250 offer reliable biological filtration without excessive flow. Use a spray bar or lily pipe outlet to spread the current gently across the tank surface rather than directing a jet at the substrate.

A reliable heater is essential. An adjustable model rated for your tank size, such as the Eheim Jager or Fluval M series, allows you to dial in the 24 to 26 °C sweet spot this species prefers. Always pair your heater with a separate thermometer (a simple glass or digital stick-on type) so you can verify the temperature independently.

Invest in a quality liquid test kit rather than strips. The API Freshwater Master Test Kit covers ammonia, nitrite, nitrate, and pH and will last for hundreds of tests. Accurate, regular testing is the single best habit you can develop for keeping sensitive species like the CW049 healthy.

Diet and feeding

In the wild, the CW049 Black Diamond Cory feeds on insect larvae, small worms, microorganisms, and organic detritus sifted from the substrate. They are true omnivores and will accept a wide variety of foods in captivity, which makes feeding straightforward once you know what they need.

A good staple is a high-quality sinking pellet or wafer designed for bottom feeders. Hikari Sinking Wafers, Sera Viformo tablets, and Repashy Bottom Scratcher gel food are all excellent options. Supplement these with frozen or live foods two to three times per week: bloodworms, daphnia, brine shrimp, and tubifex worms are all eagerly accepted. The occasional blanched courgette slice or piece of cucumber provides a bit of variety and fibre.

Feed once or twice daily, offering only as much as the group can consume within a few minutes. Corydoras are persistent foragers, so you do not need to worry about them missing a meal. However, do make sure food actually reaches the bottom of the tank, especially in community setups where faster midwater fish may intercept sinking pellets. Dropping food in just before lights-out can help ensure the corys get their share without competition.

Behaviour and temperament

The CW049 is a thoroughly peaceful fish that spends its day methodically combing the substrate with its barbels, searching for anything edible. It is a shoaling species that feels safest and behaves most naturally in groups of six or more. In smaller numbers, they tend to hide and can become visibly stressed, fading in colour and rarely venturing into the open. In a properly sized group, they are far bolder, often resting together in a favourite spot or foraging across the sand in a loose formation.

Like other Hoplisoma and Corydoras species, the CW049 is a facultative air breather. You will see individuals dart to the surface to gulp air, then return to the bottom. This is completely normal and not a sign of low oxygen, though frequent, frantic surface visits can indicate poor water quality. Another charming quirk is the “winking” motion of the eye, actually the fish tilting its eye downward slightly, which many keepers find endearing. They are most active during dawn and dusk but will forage throughout the day in a dimly lit tank.

Tank mates

Good tank mates

Fish to avoid

Breeding

Breeding the CW049 Black Diamond Cory in captivity is achievable but requires a bit of effort and preparation. Start by establishing a well-conditioned group of at least six, ideally with a ratio of two males to every female. Over several weeks, feed them heavily with protein-rich live and frozen foods, particularly bloodworms and daphnia, to bring the females into spawning condition. You will notice ripe females becoming noticeably plumper when viewed from above.

To trigger spawning, perform a large (50 to 70 percent) water change using water that is a few degrees cooler than the tank, roughly 2 to 3 °C lower. This simulates the onset of the rainy season and is the most reliable spawning trigger for Rio Negro corydoras species. Spawning typically occurs within hours of the water change and follows the classic corydoras “T position,” where the female clamps against the male’s ventral area to receive sperm before depositing adhesive eggs on smooth surfaces such as the tank glass, broad leaves, or spawning mops.

A typical clutch ranges from 30 to 80 eggs. The adults may eat the eggs if given the chance, so most breeders remove either the eggs or the adults after spawning. Eggs can be gently rolled off the glass with a finger or credit card and transferred to a small hatching container with water from the main tank, a few drops of methylene blue to prevent fungus, and gentle aeration from an airline. Eggs hatch in approximately four to five days at 25 °C. The fry absorb their yolk sac over another two to three days, after which they will accept infusoria, microworms, or powdered fry food such as Hikari First Bites. Graduate to baby brine shrimp within the first week or two as the fry grow.

Common diseases and health

The most common issue with CW049 Black Diamond Corys, and corydoras in general, is barbel erosion. This happens when fish are kept on sharp or dirty substrates. The barbels wear down, become reddened, and may develop secondary bacterial infections. Prevention is simple: use fine, smooth sand and keep the substrate clean with regular vacuuming. If barbel erosion does occur, improving water quality and substrate conditions usually allows the barbels to regenerate over time. In severe cases, a course of antibacterial treatment such as eSHa 2000 or Seachem KanaPlex may be needed.

Ich (white spot disease) can affect the CW049, especially after a stressful event like shipping or a sudden temperature drop. Look for tiny white dots on the body and fins, clamped fins, and flashing (rubbing against objects). Treat with a half-strength dose of a malachite green and formalin medication, as corydoras are sensitive to full-strength treatments. Raising the temperature to 28 °C for the duration of treatment can speed up the parasite’s life cycle and improve results.

Internal parasites are occasionally seen in wild-caught specimens. Symptoms include loss of weight despite eating, white stringy faeces, and general lethargy. A course of praziquantel-based medication (such as NT Labs Anti-Fluke & Wormer) is usually effective. Always quarantine new fish for a minimum of two to four weeks in a separate tank before adding them to an established community. This simple step prevents the introduction of disease and gives you time to observe the fish for any signs of illness.

Frequently asked questions

How many CW049 Black Diamond Corys should I keep together?

A minimum of six is recommended. Corydoras are social fish that rely on the safety of numbers, and keeping fewer than six often results in shy, stressed individuals that hide constantly and lose colour. In a larger tank, groups of eight to twelve are even better and produce more natural, confident behaviour.

Can I keep CW049 Black Diamond Corys on gravel?

Fine, smooth gravel is tolerable in a pinch, but sand is strongly preferred. Their natural foraging behaviour involves sifting sand through their gills, and sharp or coarse substrates can damage their delicate barbels over time. If you already have gravel, consider replacing it or at least creating a sand-bottomed area where the corys spend most of their time.

Why does my CW049 keep swimming to the surface?

Occasional trips to the surface to gulp air are perfectly normal for corydoras. They have a modified intestine that can absorb atmospheric oxygen, and they use this ability even in well-oxygenated water. However, if the fish are doing this constantly and seem frantic, check your water quality immediately, as it can indicate low dissolved oxygen or elevated ammonia or nitrite levels.

Is the CW049 Black Diamond Cory the same as Corydoras schultzei?

No. While both are dark-bodied corydoras from Brazil, they are distinct fish. Corydoras schultzei (now Hoplisoma schultzei) tends to have a more bronze-gold iridescence, while the CW049 is darker with a more silver-to-white sparkle. The CW number system exists specifically for undescribed species that have not yet been formally named, so the CW049 is still awaiting scientific classification.

What is the best temperature for CW049 Black Diamond Corys?

Aim for 24 to 26 °C as your everyday target. They tolerate a range of 23 to 27 °C, but stable temperatures in the middle of that range produce the best colour, activity levels, and long-term health. Avoid sudden fluctuations, as rapid temperature swings are more dangerous than a reading that is slightly high or low.

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