Night and Day Cory CW217 (Hoplisoma sp. CW217)

Choose Corydoras CW217, the Night and Day Cory

Corydoras CW217 is one of the newest coded cory catfish in the hobby. Corydoras World issued the number in 2025, and Planet Catfish lists it as the Night and Day Cory, a fitting name for a fish whose head and front half are dark charcoal and whose rear half and fins glow orange. Its current label is Hoplisoma sp. CW217; many sellers still use the older Corydoras sp. CW217.

It is a peaceful, sociable bottom-dweller of about 6 cm from the Orinoco drainage, kept like other short-snouted corys: a group of six or more, soft sand, clean water and sinking foods. Because it is new to science and to the trade, some things about it are still unknown, and we set those out plainly below.

Separate what is known from what is not

Recognise the two-tone pattern

Photographs on ScotCat, Planet Catfish and Corydoras World show a deep-bodied, short-snouted cory with a large eye. The head and the front of the body, back to about the dorsal fin, are dark slate-grey to near black. Behind that the body turns orange-amber, and the dorsal, anal and tail fins carry the same warm orange. The change from dark to light is fairly abrupt, which gives the "night and day" effect.

ScotCat notes that CW217 could turn out to be a colour variation of Hoplisoma concolor, the slate cory. Seriously Fish describes H. concolor as restricted to parts of the Orinoco system in western Venezuela, uniformly greyish, deep-bodied, with a large eye and a relatively long dorsal-fin spine, and says mature males develop an extended dorsal fin. Planet Catfish's sexing note for CW217 is the general one for the genus: females grow larger and fuller, and males have more pointed fins.

Compare it with the slate cory

We also sell the Concolor Cory, so you can compare the two side by side.

Select a group of six and plan the cost

One purchase supplies one live Corydoras CW217 in the standard size we receive. Sex is not specified, and the price is for one fish. ScotCat advises buying six or more because they are happier in a group, and OATA advises at least five for corydoras. With a rare fish that is a real outlay, so plan the whole group before you order rather than starting with one or two. The gallery images are representative of the species; the exact boundary between dark and orange varies from fish to fish.

As a newly coded fish, CW217 is likely to be wild-caught, although we cannot always confirm the origin of a batch. Treat new arrivals as wild imports: a mature tank, gentle introduction and a quiet first week.

Work from the group you intend to keep

• Six fish: the minimum ScotCat suggests for a settled group.
• Eight or more: more natural behaviour and a better chance of both sexes if you hope to breed them.
• A species tank: ScotCat suggests one for breeding, and it is the best way to see this fish's colour against plain sand.

See our delivery information before you order. More uncommon fish are in our rare and collector fish range, and other species in our corydoras range.

Give the group enough floor

OATA recommends at least 80 litres for a shoal of corydoras, and Seriously Fish gives an 80 × 30 cm base for the similarly sized H. concolor. Corys live on the floor, so the base area is what counts. Our tank volume calculator works out the litres from your tank's dimensions.

Use a three-step space check

1. Check the base: at least 80 × 30 cm of open sand for a group of six.
2. Count the floor-dwellers: add every other cory, loach and pleco to the same floor budget.
3. Keep the front open: a clear patch of sand at the front is where the group feeds and where you will see it best.

Furnish with soft sand, wood and shade

Planet Catfish describes sand as close to mandatory, with rounded gravel as an imperfect alternative and sharp or chipped gravel to be avoided, as it damages barbels. It suggests bordering the sand with driftwood and plants and giving shade from overhanging wood or floating plants. ScotCat records CW217 from a clear-water stream, so aim for clear, clean water rather than a heavily stained blackwater tank.

Divide the floor by function

Set water values and keep them stable

ScotCat gives water values for CW217. Planet Catfish gives none. Seriously Fish gives values for H. concolor, and OATA gives broad values for catfish as a group. The target column stays inside the ranges for CW217 and its possible relative.

Water from UK taps varies by region, and in many areas it is hard with a pH above 7. Test before the fish arrive and, if needed, blend in reverse osmosis water to bring hardness and pH down gradually. Our water matcher tool and water chemistry guide explain how.

Separate habitat values from waste readings

The table above describes the habitat. Waste is a separate measure: OATA's targets are zero ammonia, zero nitrite and nitrate no more than 20 mg per litre above tap water. Only add a group of corys to a tank that has finished cycling; our nitrogen cycle guide explains how to tell.

Filter well and clean little and often

Corys need well-oxygenated water without a strong current. Choose a filter rated for the whole tank and set the outlet to ripple the surface. Rinse sponges in removed tank water rather than under the tap, as OATA advises, so the bacteria that keep ammonia at zero survive.

Follow a weekly maintenance sequence

1. Test ammonia, nitrite, nitrate and pH and record them.
2. Gently siphon the open sand and lift out decaying leaves.
3. Replace about a quarter of the water with dechlorinated, temperature-matched water.
4. Top up leaf litter if you use it, a few leaves at a time.
5. Count the group at feeding time and check every fish is eating.

Feed a varied sinking diet

ScotCat says CW217 readily accepts a mixed diet of granular foods, tablets, frozen bloodworm and good flake. Planet Catfish adds live and frozen white worm, grindal worm, Daphnia and tubifex as good conditioning foods. OATA's guidance is to feed sinking foods once a day, only as much as is eaten in a few minutes.

Build one measured meal

New, wild-caught corys can be slow to feed in daylight. Feed just after lights-out for the first week or two.

Introduce the group with care

OATA's floating-bag method is to switch the aquarium lights off, float the bag for about 10 minutes to equalise temperature, then add small amounts of tank water over about 20 minutes before moving the fish across with as little bag water as possible. For sensitive or wild-caught fish, OATA describes a slower drip acclimation, which suits a valuable new import like this. Our acclimatisation guide covers both.

Use a first-week checkpoint plan

Choose peaceful company for a rare cory

Planet Catfish calls it a peaceful, shoaling community fish, and ScotCat suggests small to medium tank mates such as tetras, rasboras and danios, or a species tank. With a fish this rare, choose companions that are calm, never compete hard for food on the floor, and like the same soft, clean water. Our tank mates tool checks a combination before you buy.

Screen tank mates before mixing

Our corydoras care guide covers group living and community planning, and the South American catfish category and bottom dwellers range show other floor fish.

Watch for health changes early

OATA describes a healthy fish as having clear eyes, undamaged fins, no ulcers or bumps, normal swimming and steady breathing. In corys, also look at the barbels, which wear down on sharp or dirty substrates. The dorsal and pectoral spines catch in net mesh, so move these fish with a fine, soft net or a small container.

Pair each observation with an action

Record any breeding you see

There is no breeding report for CW217 on Planet Catfish, and the full Corydoras World record is for members only. ScotCat suggests a species tank for breeding, as with other corys. If your group spawns, OATA notes that cory eggs stuck to glass and décor seldom survive in the main tank unless they are moved and raised separately. An aquarium spawning of a newly coded fish is worth recording and sharing with Planet Catfish or Corydoras World.

Answer Corydoras CW217 buying questions

What is Corydoras CW217?

It is an undescribed cory catfish, coded CW217 by Corydoras World in 2025 and now labelled Hoplisoma sp. CW217. Planet Catfish lists the common name Night and Day Cory, after its dark front half and orange rear half.

Is CW217 a form of the slate cory, Hoplisoma concolor?

Possibly. ScotCat says it could turn out to be a colour variation of H. concolor, which comes from the same Orinoco river system. Until someone studies it properly, it keeps its CW code.

Where does it come from?

ScotCat records a clear-water tributary of the Río Tomo and also lists Bolívar State in Venezuela and the Río Meta basin in Colombia. All of these drain to the Orinoco. The exact locality is not settled in the published sources.

How big does it grow?

ScotCat gives about 6.0 cm for males and 6.5 cm for females.

How many should I keep?

ScotCat advises buying six or more, as they are happier in a group, and OATA advises groups of at least five for corydoras.

What water does it need?

ScotCat gives 22–25°C and pH 6.0–7.5. Clean, soft to moderately hard water at 23–25°C, with zero ammonia and nitrite, suits it well.

What does it eat?

A varied diet of sinking granules and tablets, quality flake, and frozen bloodworm, as ScotCat recommends, with occasional live foods such as Daphnia or white worm.

Why is it more expensive than common corys?

It is a newly coded fish that reaches the UK only in small numbers. The price is for one fish, so plan the cost of a group of six before you order.

Consult the care references

• Planet Catfish: Hoplisoma sp. (CW217): names, genus, sexing, feeding, substrate, décor and compatibility.
• ScotCat: Hoplisoma sp. (CW217) factsheet: when the number was issued, possible link to H. concolor, lineage, distribution, adult sizes, water values and diet.
• Corydoras World: Hoplisoma sp. CW217: the Corydoras World species record and photographs for Hoplisoma sp. CW217.
• Seriously Fish: Hoplisoma concolor (slate cory): size, aquarium base, water values and colour of Hoplisoma concolor, the slate cory.
• ScotCat: "What the heck is a CW number?" (Rob McLure): what C and CW numbers are, and the story of how CW127 was separated from C. parallelus.
• Dias et al. 2024, Zoological Journal of the Linnean Society: the 2024 classification that moved most species out of Corydoras into Hoplisoma, Brochis and other genera.
• OATA: How to look after freshwater catfish: UK guidance for catfish on water quality, sand, introduction, handling, feeding and health signs.
• OATA: How to look after wild caught freshwater fish: UK guidance on acclimatising sensitive or wild-caught fish, including drip acclimation.
• Tropical Fish Co delivery policy: current dispatch days and Live Arrival Guarantee terms.