• Species: Corydoras ambiacus

  • Species: Corydoras arcuatus

  • Species: Corydoras caudimaculatus

  • Species: Corydoras duplicareus

  • Species: Corydoras melanistius

  • Species: Corydoras melini

  • Species: Corydoras robinae

  • Species: Corydoras schwartzi

  • Species: Corydoras septentrionalis

  • Species: Corydoras virginae

  • Species: Corydoras eques

Focus on Corydoras

18 August 2017


Many aquarists spend a lot of their time hunting through shops for unusual catfish, rare plecs and predatory catfish. But for aquarists after something a bit more manageable, there are also a wide selection of Corydoras catfish. These schooling catfish generally only get to about 5-7 cm in length and are completely peaceful towards other fish, even livebearer fry. Even better, they are generally very easy to keep and adapt to a wide range of water chemistry conditions, making them just about the best bottom feeding fish for most aquaria.

Most aquarium stores carry two Corydoras species, the peppered Corydoras and the bronze Corydoras. A few other species, notably the Corydoras panda and Corydoras trilineatus, are also quite widely sold (the latter species most often under the Corydoras julii name). But for the aquarist after some of the less commonly traded species, finding the right Corydoras for their tank can be difficult. Fortunately, many shops regularly keeps a selection of unusual Corydoras in stock alongside the popular bread-and-butter species.

Because Corydoras are air-breathers and naturally come from habitats where the water temperature can be quite variable, they generally ship well. So if you aren’t able to visit a shop in person, consider visiting their online store. For online purchases you need look no further than Wildwoods which carry a comprehensive range of Corydoras species. To see the full selection of Corydoras available, look in the “Catfish - Callichthyidae” section within their Tropicalfish2yourdoor shop. Corydoras are invariably best kept in groups, and to make this easier on your pocket, Wildwoods are currently offering a 5% discount on mail order purchases of five or more specimens of many of their Corydoras species.

Basic care

Most Corydoras need to be kept in the same sort of way. All are gregarious, and should be kept in groups of six specimens per species. While different species will get along together just fine, they don’t necessarily view one another as companions, so if you want two different species, then get at least six of each.

All Corydoras feed by ploughing through the sediment looking for algae, small invertebrates, and any other edible organic matter they can find. Under aquarium conditions they prefer tanks with a sand rather than gravel substrate, and the aquarist will certainly find their fish more fun to watch when kept that way.

Although it is doubtful gravel actually wears down their barbels, it is certainly true that dirty gravel can host bacteria that cause catfish barbels to become infected and degraded over time. Corydoras find it much easier to keep sand clean and well turned over that specimens kept in tanks with a sandy substrate often have much longer barbels than identical species kept in tanks with gravel. That said, not all sand is safe for use with catfish, and you should always use sand known to be safe with burrowing fish. Some popular aquarium sands are not, being too sharp and abrasive; Tahitian Moon Sand is one example of a sand not suitable for use with burrowing fish including Corydoras. A cheap and safe choice is smooth silica sand, sometimes called smooth silver sand, a product widely sold in garden centres; a 25 kg bag of the stuff will only cost £3-4.

Feeding Corydoras will push their heads into the sediment, spewing sand out through their gills as they sift out food particles. Providing the right foods is easy, as most anything will be accepted. Frozen bloodworms and small crustaceans are favourites, but standard flakes, pellets and algae wafers work well too.

Water chemistry is not critical, and most species thrive across a broad range of values. Aim for a water hardness level between 5-20 degrees dH and a pH between 6 and 8. In the short term Corydoras tend to be tolerant of occasional water quality problems, but like any other fish you should try to ensure good water quality all the time. Proper filtration and regular water changes are essential.

Water temperature requirements vary between species. Most prefer water a little cooler than normal, and do best between 22-25 degrees C (72-77 degrees F). As such, they’re ideal companions for other fish that like relatively cool conditions including neons, platies, swordtails, barbs and danios. Only a few genuinely enjoy water temperatures above 25 degrees C (77 degrees F), and when exposed to consistently high water temperatures these fish will exhibit signs of stress such as skittishness and unusually rapid breathing.

Corydoras are facultative air breathers, meaning that they can adjust to water that doesn’t contain enough oxygen by swimming to the top of the tank to breathe air. The warmer water becomes, the less dissolved oxygen it can hold, so the frequency with which these catfish gulp air is closely related to water temperature. In very deep tanks Corydoras may have trouble reaching the surface comfortably, and it should be remembered that these are fish of shallow streams, not rivers. All species do best in tanks less than 60 cm (2 feet) in depth, and the smaller species, those around 5 cm (2 inches) in length, would be better kept in tanks under 45 cm (18 inches) in depth.

Corydoras acutus

One of the few Corydoras that genuinely prefers warmer water conditions, Corydoras acutus is a species that gets to about 7 cm (2.75 cm) in length and is distinguished by its elegantly marked tail fin and the big black patch on its dorsal fin. It comes from the Upper Amazon region and does well between 25-28 degrees C (77-82 degrees F). As such, it’s a particularly good species to keep in tanks where above-average water temperature is required, for example for the maintenance of species such as discus, cardinal tetras or gouramis.

Corydoras agassizii

At up to 7 cm (2.75 inches) this is one of the larger Corydoras and in groups can work particularly well in community tanks that contain boisterous (rather than downright aggressive) tankmates such as swordtails, angelfish, large tetras and so on. It is attractively marked, with black spots against a silvery-pink body. A vague black patch is present around the base of the dorsal fin, and a bolder black band passes through the eye. Between these black markings is a shimmering yellow or orange band.

Corydoras ambiacus

A very infrequently traded catfish, this species has an attractive pattern of black spots across its otherwise silvery body. There are black patches cross the face and the base of the dorsal fin, and between them a bright yellow or orange saddle that crosses the dorsal surface and runs down the sides of the head onto the gill covers. Maximum length is about 6.5 cm (2.75 inches). Overall care similar to most other Corydoras, with relatively cool conditions between 20-25 degrees C (68-77 degrees F) being essential for long term success.

Corydoras arcuatus

A great favourite, this catfish has a thick black band that arcs upwards from the snout through the eye, underneath the dorsal fin, and then down the flank towards the lower lobe of the tail fin. The body colour is more or less silvery-pink, but with a distinctive metallic sheen that varies from copper to gold depending on the light. Healthy and happy groups of these catfish are stunning, but this is one of the more sensitive catfish, or at least one of the species that does poorly in immature or badly maintained aquaria. So while newcomers to the hobby are often desperate to keep a few, this Corydoras is best purchased after their tank has been properly established and allowed to settle down for a few months. There are two sorts of Corydoras arcuatus on the market, the standard variety that gets to about 5 cm (2 inches) in length and the so-called “Super Arcuatus” that is bigger, getting to as much as 7 cm (2.75 cm) in length. This latter variety may turn out to be a true species in its own right. Both varieties are maintained in the same way, and do well in any mature aquarium that isn’t too warm.

Corydoras caudimaculatus

This very attractive species gets it scientific name from the big black patch on the caudal peduncle. Otherwise the fish is pinkish-brown with faint brown spots on the head and fins. There is usually a certain amount of golden colouration across the cheeks and the base of the pectoral fins. Maximum length is less than 5 cm (2 inches) but the overall build is quite stocky. A good community fish, though as with most other members of the genus Corydoras, these catfish do best when kept at moderate temperatures, between 22-25 degrees C (72-77 degrees F) being recommended.

Corydoras duplicareus

This is a small but beautifully marked species, rarely traded and often expensive, but definitely worth keeping. Body colour is essentially silvery-pink, with a thick vertical band on the head and a black horizontal band running along the top half of the flank from below the dorsal fin towards the upper lobe of the tail fin. Between these two black bands is a bright lemon yellow band that passes from the dorsal surface right the way down to just in front of the pectoral fins. Despite its exotic colours, this species isn’t difficult to keep provided the water is fairly cool, ideally between 20-25 degrees C (68-77 degrees F). Maximum length is about 5 cm (2 inches).

Corydoras eques

Resembling the more widely traded bronze catfish Corydoras aeneus in overall colouration, Corydoras eques can be distinguished by the bright orange band between the head and the flanks. This species is also a little smaller at just over 5 cm (2 inches) or so in length, and also a little more stocky in build. An excellent community tank resident when kept along species that do not need high temperatures.

Corydoras melanistius

These strikingly marked catfish have a pinkish body covered with tiny brown spots. A thick dark band passes obliquely across the head and through the eye, and a big black patch covers part of the dorsal fin and the adjacent region of the flank. Between these two black markings is bright coppery or golden band running from the top of the head almost to the base of the pectoral fin. This is quite a small species, getting to a little over 5 cm (2 inches) in length, but stockily built, and very attractive when kept in decent sized groups. Not difficult to keep, but like most other Corydoras prefers water that is not too warm. The tail fin of this species is unmarked, but for a time a subspecies with spots on its tail fin was recognised, known as Corydoras melanistius brevirostris. That fish is now treated as a distinct species in its own right, Corydoras brevirostris, though in terms of care the two fish are very similar.

Corydoras melini

An old favourite, though less frequently traded than some of the other popular Corydoras species. Body colour is silvery-pink with two thick black bands, one running obliquely through the eye, and the other L-shaped, running first down the dorsal fin, and then bending backwards to run along the flank and onto the lower lobe of the tail fin. It is a relatively small species at a mere 4.5 cm (1.75 inches) in length, though stocky, and with its bright markings certainly not a fish that lacks presence. In a reasonably large group this catfish will be a delightful addition to any small community aquarium kept at no more than 26 degrees C (79 degrees F).

Corydoras metae

Sometimes called the “bandit catfish” on account of the black band across its face, this is an attractive species frequently confused with the very similar Corydoras melini. The big difference between the two species is the oblique black band on the flank. On Corydoras melini, this band runs onto the lower lobe of the tail fin, whereas on Corydoras metae, the black band stops at the caudal peduncle and does not carry onto the tail fin itself. Otherwise the two species are very similar in terms of care.

Corydoras nattereri

This is a relatively cool climate species that does best between 20-22 degrees C (68-72 degree F) and as such is ideally suited to life alongside hillstream and subtropical fish including danios, minnows and some of the barbs and gobies. Although not brilliantly coloured, it has a neat black horizontal marking set against its essentially silvery body. Groups are attractive, and under the right conditions this species is hardy and easy to maintain. Very rarely traded, this may be a species for the connoisseur, but a worthy aquarium fish nonetheless.

Corydoras robinae

One of the most distinctive of all the Corydoras available, this little catfish has bold black and white horizontal bands on its tail fin that blend into the horizontal banding on the flanks. The body is essentially silvery, except for the more coppery-coloured head. Healthy specimens are stunning fish, comfortably earn pride of place in whatever community tank they’re added to. In common with most Corydoras, they do best in tanks that are a little on the cool side, and should not be kept above 25 degrees C (77 degrees F). Otherwise undemanding and generally easy to keep. Maximum length is about 6.5 cm (2.75 inches).

Corydoras schwartzi

This uncommonly traded species with particularly interesting markings that consist of a bold vertical black band on the head and a series of horizontal bands and rows of spots along the flanks. The tail fin is marked with vertical arrangements of small black spots. Separating the black band on the head and the markings on the flanks is a vertical yellowy patch that shimmers depending on the ambient lighting. A fairly large species, getting to about 7 cm (2.75 inches) in length. Maintenance similar to the majority of other Corydoras, with this species doing best in relatively cool conditions not above 25 degrees C (77 degrees F).

Corydoras septentrionalis

This species is very infrequently traded but well worth looking out for. It is highly distinctive, having a relatively long and streamlined body and a very long snout with equally well developed whiskers. Colouration is variable, but typically sandy-coloured with a dark band through the eye, a dark patch across the base of the dorsal fin, and a dark patch on the caudal peduncle. There are several vertical dark stripes on the tail fin. Some smudgy dark patches will be apparent on the adipose fin and on the flank just above and behind the pectoral fins. The gill covers and the region around the pectoral fin base is golden. Corydoras septentrionalis is medium sized species at about 6 cm (2.5 inches) in length. It needs an aquarium with clean water, a decent current, and not too much heat.

Corydoras similis

This decorative species is known as the “smudge-spot catfish” thanks to the indistinct greenish-black patch that covers the caudal peduncle. Otherwise it is basically pinkish-brown in colour with a coppery-coloured head covered with neat brown speckles. Maximum size is only 5 cm (2 inches) and consequently this species is best kept with small, gentle tankmates. It isn’t shy though, and a school of these catfish will work well in any suitable community tank. A versatile species that does well across a broad temperature range, from 21-28 degrees C (70-82 degrees F).

Corydoras virginiae

A bold and robust catfish that works well in community tanks alongside any fish that isn’t overly aggressive or predatory. It is essentially pinkish-brown in colour, with a slight silvery sheen, but with two vertical black bands, one on the head and another running from the base of the dorsal fin about two-thirds of the way down the flank. Between these bands is a bright yellow-orange vertical band. At about 6 cm (2.5 inches) this is a medium-sized species in terms of length, but has a distinctly stocky build. Not a commonly traded species, but an excellent all-around bottom feeder for any community tank kept at middling temperatures around 23-27 degrees C (73-81 degrees F).