Delphax Cory

Quick Summary

The Delphax Cory is a gentle, sociable catfish that thrives in groups of six or more on a soft sand substrate – an excellent bottom-dwelling addition for community tanks kept by beginners and experienced aquarists alike, provided the water is kept clean and slightly soft.

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In this guide:

• Introduction
• Quick Stats
• Appearance
• Natural Habitat
• Tank Size and Setup
• Water Parameters
• Diet and Feeding
• Behaviour and Temperament
• Tank Mates
• Breeding

Introduction

Corydoras delphax, commonly known as the Delphax Cory, is a small armoured catfish belonging to the family Callichthyidae. Native to the river systems of Colombia in South America, this species has steadily gained a following among freshwater hobbyists who appreciate its peaceful disposition, attractive patterning, and engaging group behaviour. Like all members of the Corydoras genus, the Delphax Cory is a bottom-dweller that spends much of its time sifting through the substrate in search of food, making it an invaluable part of a well-balanced community aquarium.

Historically, some references and retailers have listed this species under the older genus placement Brochis delphax. While you may still encounter that name on older websites or in legacy stock lists, the currently accepted scientific name is Corydoras delphax, and that is the designation used throughout this guide. The distinction matters primarily for taxonomic accuracy; care requirements are consistent regardless of which label you find attached to the fish at your local shop.

One of the most appealing aspects of keeping Delphax Corys is their strong shoaling instinct. These fish are genuinely happier – and healthier – when kept in groups. A solitary Corydoras often becomes reclusive and stressed, whereas a group of six or more will confidently explore every corner of the tank floor, displaying natural foraging behaviours and the characteristic “winking” eye movement that Corydoras enthusiasts find so endearing. If you are looking for a low-aggression, easy-to-feed bottom-dweller that adds both activity and charm to the lower reaches of your aquarium, the Delphax Cory is well worth considering.

Appearance

The Delphax Cory is a compact, somewhat laterally compressed catfish with the typical Corydoras body plan: a broad, rounded head tapering to a slightly narrower caudal peduncle, covered in two rows of overlapping bony scutes rather than conventional scales. These armoured plates give the fish a subtly ridged texture along its flanks and provide a degree of protection against predators in the wild.

The base body colour ranges from pale silvery-grey to a warm cream, overlaid with a bold pattern of dark blotches and spots. A prominent dark saddle-like marking typically extends across the dorsal region just behind the head, and a large blotch is present on the dorsal fin itself, which is one of the most reliable visual identifiers for the species. The flanks display an irregular arrangement of smaller dark spots or dashes that can vary in density between individuals. The ventral surface is generally unmarked and lighter in colour.

The fins are largely transparent to pale yellow, though the dorsal fin carries the distinctive dark blotch already mentioned, and the caudal fin may show faint vertical barring. The pectoral fins bear a stout, serrated leading spine – a defensive adaptation common across the Corydoras genus that is worth bearing in mind when netting the fish, as the spines can become entangled in fine mesh.

Like all Corydoras, the Delphax Cory possesses three pairs of barbels around the mouth. These sensory organs are essential for locating food in the substrate and are easily damaged by sharp or coarse gravel, which is why a soft sand substrate is strongly recommended. Healthy barbels should be long and intact; eroded or shortened barbels are a clear sign of substrate-related injury or bacterial infection.

Males and females are broadly similar in appearance. When viewed from above, mature females tend to be slightly wider and rounder in the body, particularly when carrying eggs. Males are typically a touch slimmer and may appear marginally smaller overall, though these differences are subtle and most reliably observed in a well-conditioned group.

Natural Habitat

Corydoras delphax originates from the Orinoco River basin in Colombia, with collections documented primarily from the Rio Inirida and Rio Meta drainages. These waterways flow through tropical lowland regions characterised by warm temperatures, moderate to soft water chemistry, and substrates composed predominantly of fine sand, silt, and leaf litter.

In their natural environment, Delphax Corys inhabit relatively slow-moving stretches of rivers and streams, as well as flooded forest margins during the wet season. The water tends to be slightly acidic to neutral, stained to varying degrees by tannins released from decomposing plant matter. The substrate is typically soft and silty, which allows the fish to forage freely without damaging their delicate barbels.

The surrounding vegetation in these habitats includes marginal plants, submerged roots, and fallen branches, all of which provide shelter and create the shaded conditions that Corydoras species generally prefer. Leaf litter on the stream bed serves both as a food source – hosting biofilm, microorganisms, and small invertebrates – and as cover from aerial and aquatic predators.

Understanding this natural setting is key to replicating appropriate conditions in captivity. The Delphax Cory does not come from fast-flowing, highly oxygenated rapids, nor from stagnant, oxygen-poor pools. Instead, it thrives in gently flowing water with good but not excessive current, moderate lighting, and plenty of cover at the substrate level. Recreating even a simplified version of this environment will help the fish feel secure and encourage natural behaviours.

Tank Size and Setup

A minimum tank size of 80 litres is recommended for a group of six Delphax Corys. While these are not large fish, they are active foragers that benefit from a generous footprint of open substrate. A tank measuring approximately 80 cm in length provides a suitable base area. If you plan to keep a larger group – which is always encouraged with Corydoras – or to house them in a community setting with other species, a tank of 120 litres or more is preferable.

Substrate choice is critical. Delphax Corys, like all Corydoras, feed by plunging their barbels into the substrate and sifting through particles to locate food. Sharp or rough gravel can abrade and erode these sensitive sensory organs, leading to infection and reduced feeding efficiency. Fine, smooth sand – such as play sand, pool filter sand, or purpose-sold aquarium sand – is the only appropriate substrate. Avoid crushed coral, sharp-edged gravels, or any substrate with angular particles.

Aquascaping should aim to provide a mix of open foraging areas and sheltered resting spots. Driftwood, smooth rocks, and hardy plants such as Anubias, Java Fern, and Cryptocoryne species all work well. Floating plants are a useful addition, as they diffuse overhead light and create the shaded conditions that make Corydoras feel more comfortable. Dried Indian almond leaves or other botanicals placed on the substrate add a naturalistic touch and release beneficial tannins as they decompose.

Ensure that there are no sharp decorations or ornaments with narrow openings where a Corydoras could become trapped. These fish sometimes wedge themselves into tight spaces and, with their pectoral spines locked, can struggle to reverse out. Smooth, rounded decor is always the safest option.

Lighting should be moderate. While the Delphax Cory does not have specific lighting needs, intense overhead illumination can make these bottom-dwellers feel exposed and encourage them to remain hidden. A planted tank with moderate lighting and some floating cover tends to bring out the most confident behaviour.

Water Parameters

Maintaining stable, clean water is arguably more important than hitting exact numbers on a test kit. That said, the Delphax Cory does best within the following ranges, which reflect the soft, slightly acidic to neutral conditions of its natural habitat.

Corydoras are sometimes described as hardy, and while there is truth to this, they are notably sensitive to poor water quality – particularly elevated nitrate levels and dissolved organic waste. Ammonia and nitrite must always read zero in an established tank. Regular partial water changes of 20 to 30 per cent weekly are recommended to keep nitrate levels in check and maintain overall water quality.

Temperature stability is important. Sudden swings of more than a couple of degrees can stress the fish and weaken their immune response. When performing water changes, match the replacement water’s temperature as closely as possible to the tank water. Using a thermometer to check incoming water is a simple habit that prevents unnecessary thermal shock.

If your tap water is particularly hard or alkaline, consider blending it with reverse osmosis (RO) water to bring the parameters closer to the species’ preferred range. However, most Delphax Corys bred in captivity or acclimatised by importers will tolerate moderately hard water without issue, provided the pH does not climb significantly above 7.5 and the water remains clean.

Filtration and Equipment

A reliable filter rated for the tank’s volume is essential. Corydoras are sensitive to ammonia and nitrite, so robust biological filtration should be the priority. Hang-on-back filters, internal power filters, and canister filters all work well. Sponge filters are another excellent option, particularly in breeding setups, as they provide gentle flow and pose no risk of trapping fry.

Flow rate should be moderate. The Delphax Cory does not come from torrential rapids, and excessive current directed along the substrate can make foraging difficult and stress the fish. If your filter produces a strong output, angle the flow towards the surface or use a spray bar to disperse it. A gentle circulation throughout the tank is ideal – enough to prevent dead spots and ensure even oxygen distribution without buffeting the fish.

An adjustable heater is necessary to maintain the temperature within the recommended 22 to 26 C range. Choose a heater appropriate for the tank’s volume and position it near the filter outflow to aid even heat distribution. A separate thermometer – digital or glass – provides an independent check on the heater’s accuracy and should be considered standard equipment.

Lighting, as mentioned, should be moderate. A standard LED unit suitable for low to medium light plants is more than adequate. If your fixture is particularly bright, floating plants or a dimmer function will help soften the light reaching the substrate level.

An air pump is not strictly required if the filter provides adequate surface agitation, but Corydoras do periodically dart to the surface to gulp atmospheric air. This is a normal supplementary breathing behaviour and not a sign of distress, provided it occurs only occasionally. If you observe constant, frantic surface breathing, check your dissolved oxygen levels and increase surface agitation.

Diet and Feeding

The Delphax Cory is an unfussy omnivore that readily accepts a wide variety of foods. In the wild, its diet consists of small invertebrates, insect larvae, detritus, and biofilm grazed from surfaces and sifted from the substrate. In captivity, replicating this dietary breadth is straightforward and important for long-term health.

A high-quality sinking pellet or wafer designed for bottom-feeding catfish should form the staple diet. These foods are formulated to sink quickly and soften on the substrate, allowing the Corydoras to forage naturally. Avoid relying on flake food alone, as much of it is consumed by mid-water and surface-dwelling tank mates before it ever reaches the bottom.

Supplement the staple diet with frozen or live foods such as bloodworm, daphnia, brine shrimp, and tubifex. These protein-rich additions are particularly valuable for conditioning fish prior to breeding, but they also contribute to overall vitality and colour. Blanched vegetables – courgette rounds, cucumber slices, and shelled peas – are accepted by some individuals and add variety to the diet.

Feed once or twice daily, offering only as much food as the group can consume within a few minutes. Uneaten food left on the substrate will decompose and degrade water quality, which is particularly problematic in the low-flow zones near the bottom of the tank where Corydoras spend their time. Remove any uneaten portions promptly.

It is a common misconception that Corydoras can survive solely on leftover food that falls from above. While they do scavenge, they cannot be relied upon as a tank cleaning crew, and they require targeted feeding to meet their nutritional needs. Always ensure food reaches the substrate for them.

Behaviour and Temperament

The Delphax Cory is a quintessentially peaceful species. It shows no aggression towards tank mates, does not defend territory, and has no inclination to nip fins. Its interactions with other fish are limited to occasionally being startled by sudden movements nearby, at which point it may dart away briefly before settling back into its foraging routine.

Shoaling behaviour is central to the Delphax Cory’s wellbeing. A minimum group of six is essential, and larger groups of eight to twelve or more will produce even more confident, active fish. In a well-sized group, individuals will forage together, rest in clusters, and periodically engage in synchronised swimming along the tank floor. Solitary or paired Corydoras tend to hide, eat less, and show signs of chronic stress.

Like other Corydoras species, the Delphax Cory is primarily crepuscular – most active during dawn and dusk. In a home aquarium, feeding times typically stimulate the most visible activity. During the middle of the day, particularly under bright lighting, groups may rest together in a favoured shaded spot. This is normal behaviour and not a cause for concern.

The characteristic surface dash – in which the fish rockets to the water surface, takes a gulp of air, and descends again – is a perfectly normal behaviour in all Corydoras. These catfish possess a modified intestinal lining that can absorb atmospheric oxygen, supplementing their gill respiration. Occasional surface dashes are nothing to worry about, though frequent, sustained gulping can indicate low dissolved oxygen or poor water quality.

Corydoras are also known for their “eye blinking” or “winking” behaviour, in which they rapidly rotate their eyes downward and back. This is a unique trait of the genus and is thought to be related to adjusting the position of the eye within the socket. It is completely harmless and, for many keepers, one of the most charming aspects of the fish.

Tank Mates

The Delphax Cory’s gentle nature makes it compatible with a broad range of similarly peaceful community fish. The primary considerations when selecting tank mates are temperament, size, and environmental preferences. Avoid any species that is aggressive, territorial at the substrate level, or large enough to view a Corydoras as food. Similarly, very boisterous or fast-feeding species can outcompete Corydoras at feeding time, leading to malnutrition if the keeper does not take steps to ensure food reaches the bottom.

Good tank mates

• Cardinal Tetra – A classic peaceful mid-water schooler that shares a preference for soft, slightly acidic water.
• Ember Tetra – Tiny and completely non-threatening, these tetras occupy the mid-water column and complement Corydoras beautifully.
• Harlequin Rasbora – A calm, hardy rasbora that thrives in overlapping water parameters and ignores bottom-dwellers entirely.
• Rummy-Nose Tetra – Tight schooling behaviour keeps these tetras in the mid-water zone, well away from the substrate.
• Kuhli Loach – Another peaceful bottom-dweller that coexists without competition, especially in well-planted tanks with ample floor space.
• Otocinclus – Gentle algae grazers that occupy different microhabitats and pose zero threat to Corydoras.
• Honey Gourami – A mild-mannered surface and mid-water species that makes an excellent centrepiece in a Corydoras community tank.
• Cherry Barb – One of the most peaceful barb species, compatible in temperament and water parameter preferences.

Fish to avoid

• Oscar – Far too large and predatory; an adult Oscar would readily consume a Corydoras.
• Jack Dempsey – Highly aggressive and territorial, especially around the substrate where Corydoras forage.
• Red-Bellied Piranha – An obvious predation risk for any small, slow-moving bottom-dweller.
• Common Pleco – Not aggressive per se, but grows extremely large, produces excessive waste, and can inadvertently bully smaller bottom-dwellers as it matures.
• Tiger Barb – Notorious fin nipper that can harass slower species, particularly in insufficiently sized groups.
• African Cichlids (Mbuna) – Require hard, alkaline water incompatible with Corydoras preferences, and are often highly aggressive.
• Red-Tail Catfish – A massive predatory catfish entirely unsuitable for community aquaria.

Breeding

Breeding the Delphax Cory in captivity is achievable for dedicated hobbyists, though it requires some preparation and patience. Like most Corydoras species, spawning can be triggered by simulating the onset of the rainy season – a technique that replicates the natural environmental cues the fish would experience in the wild.

Begin by conditioning a group of healthy adults with generous portions of high-protein live and frozen foods for two to three weeks. Bloodworm, brine shrimp, and daphnia are all excellent conditioning foods. During this period, ensure water quality is impeccable, as stressed or undernourished fish are unlikely to spawn.

To trigger spawning, perform a large water change of around 50 per cent using water that is a few degrees cooler than the tank temperature. This drop in temperature, combined with the influx of fresh water, mimics the arrival of cool rainwater and is often sufficient to stimulate breeding behaviour within 24 to 48 hours. Some breeders also reduce the water level slightly before refilling, or increase aeration to add further environmental cues.

Spawning behaviour in Corydoras follows a distinctive pattern. Males will actively pursue females, nudging them around the body. When a female is receptive, she will assume the characteristic “T-position” with a male, pressing her mouth against his ventral area. It is believed that during this embrace, sperm is taken in and passes through the female’s digestive tract to fertilise the eggs as they are released. The female then cups a small clutch of adhesive eggs between her pelvic fins, swims to a suitable surface – typically a plant leaf, the tank glass, or a smooth piece of decor – and deposits them firmly. This process is repeated many times over several hours, resulting in eggs scattered across multiple locations throughout the tank.

Egg clutches typically number between 50 and 200 in total. The eggs are relatively large for the genus, pale and slightly amber in colour, and quite sticky. Fertile eggs remain translucent or develop a slight amber tint, whereas infertile eggs turn white and opaque within a day or two.

Adult Corydoras may consume their own eggs if given the opportunity, so it is advisable to either remove the adults to a separate tank after spawning or carefully transfer the eggs to a dedicated hatching container. A small, well-aerated container with water drawn from the spawning tank works well. Adding a few drops of methylene blue to the hatching water can help prevent fungal growth on the eggs.

Eggs typically hatch within four to five days at around 24 C. The newly emerged fry are tiny and will initially absorb their yolk sacs over the following day or two. Once free-swimming, they can be fed infusoria, commercially available liquid fry food, or microworms. As they grow, gradually transition them to freshly hatched baby brine shrimp and finely crushed dry foods. Maintain excellent water quality in the fry tank with gentle sponge filtration and frequent small water changes.

Common Diseases

The Delphax Cory is a reasonably robust species when kept in appropriate conditions, but it is susceptible to several common freshwater ailments, particularly when water quality deteriorates or the fish is subjected to chronic stress.

Barbel erosion is perhaps the most frequently encountered issue specific to Corydoras. Caused by rough or sharp substrates, bacterial infection, or persistently poor water quality, it manifests as shortened, blunted, or reddened barbels. Prevention is straightforward: use fine, smooth sand and maintain clean water. If erosion is already present, improving substrate and water conditions will often allow the barbels to regenerate over time, though severe cases may require antibiotic treatment.

White spot disease (Ichthyophthirius multifiliis), commonly known as ich, presents as small white cysts on the body and fins. It is highly contagious and often introduced through new, unquarantined fish. Treatment typically involves raising the temperature gradually to around 28 C and administering a suitable white spot medication. Note that Corydoras are sensitive to many medications, particularly those containing copper or malachite green at full strength. Always use medications at half the recommended dose unless the product is specifically labelled as safe for scaleless fish, and monitor the fish closely during treatment.

Fin rot, characterised by fraying, discolouration, or recession of the fin edges, is usually a secondary bacterial infection arising from poor water conditions or physical damage. Improving water quality through more frequent water changes is often sufficient to halt and reverse mild cases. More advanced fin rot may require treatment with a broad-spectrum antibacterial medication.

Corydoras can also be affected by internal parasites, particularly wild-caught specimens. Symptoms may include weight loss despite normal feeding, bloating, or white, stringy faeces. An anti-parasitic food or medication suitable for freshwater catfish can address most common internal parasites.

Preventative care is always preferable to reactive treatment. Quarantine all new fish for a minimum of two weeks before introducing them to an established tank, maintain consistent water quality, and provide an appropriate diet. A healthy, well-maintained Corydoras has a strong immune system and is unlikely to succumb to disease under normal circumstances.

FAQs

How many Delphax Corys should I keep together?

A minimum of six is strongly recommended. Corydoras are obligate shoaling fish, and keeping them in smaller numbers leads to increased stress, reduced activity, and a noticeably less engaging display. Groups of eight to twelve or more are even better if your tank size permits. You will see far more natural behaviour – synchronised foraging, group resting, and confident exploration – in a properly sized shoal.

Can I keep Delphax Corys on gravel instead of sand?

It is not recommended. Corydoras feed by plunging their sensitive barbels into the substrate, and rough or sharp-edged gravel can cause barbel erosion, infection, and pain. Fine, smooth sand is the only truly appropriate substrate for any Corydoras species. If you must use gravel elsewhere in the tank, ensure that at least a significant area of the bottom is covered with sand to provide a safe foraging zone.

Why does my Delphax Cory keep darting to the surface?

Occasional surface dashes are completely normal. Corydoras possess a specialised section of intestinal lining capable of absorbing atmospheric oxygen, and they periodically gulp air at the surface to supplement their gill respiration. However, if you observe constant, frantic surface breathing, it may indicate low dissolved oxygen levels or deteriorating water quality. Check your water parameters and increase surface agitation to improve gas exchange.

Is the Delphax Cory the same as Corydoras blochi?

No. Corydoras delphax is sometimes sold under the trade name “False Blochi Cory” because of its superficial resemblance to Corydoras blochi, but they are distinct species. The Delphax Cory typically shows a bolder, more defined dark blotch on the dorsal fin and a different spotting pattern along the flanks. If in doubt, purchase from a reputable dealer who uses correct scientific names.

Do Delphax Corys eat algae?

Not to any meaningful extent. While Corydoras may incidentally ingest small amounts of algae or biofilm while foraging, they are not effective algae eaters and should not be purchased with that expectation. If you need algae control, consider dedicated algae grazers such as Otocinclus or Nerite snails. Delphax Corys require targeted feeding with sinking pellets, wafers, and supplementary live or frozen foods.

Related Guides

• Bronze Cory – One of the most widely kept Corydoras species, with very similar care requirements and an excellent comparison point for beginners.
• Panda Cory – Another popular small Corydoras species that thrives in identical tank setups and community environments.
• Sterbai Cory – A slightly warmer-water Corydoras often kept alongside discus, useful for understanding the genus’s temperature range.
• Pygmy Cory – A miniature Corydoras species with unique mid-water swimming behaviour, ideal for nano setups.
• Otocinclus – A peaceful bottom-dwelling algae eater that pairs exceptionally well with Corydoras in planted community tanks.