View Full Version : Corydorus Catfish: A Primer

07-04-2008, 06:46 AM
Corydoras catfish are one of the bread and butter fishes of the aquarium hobby, and have been since the 1930's. Bewhiskered charmers, Corydoras cats are, in many minds, THE catfish to buy for your tank.
It's the winking charm and droll attitude that makes Corys so popular. In this post, I'll demystify keeping these fish, as properly kept, Corys offer years of enjoyment. Keeping Corys in groups is the thing to do, for their security and your enjoyment. A dozen of the smaller species in a 55 gallon is not too many. Double or triple that for the tiny dwarf species.

First, nomenclature. The Genus name - Corydoras, was erected in 1803 by the French naturalist Bernard Germain de Lacιpθde with the first discovered and described species; Corydoras geoffroy. At the time he thought the head of the fish was covered by bony plates (it isn't), so he called it Cory for a cuirass (a helmet) and doras for skin, which in this case was on the head. He anglicized the Greek 'Kory' for the Genus name. So Corys are literally 'helmet headed'.

Since that time over 350 species of Corydoras have been discovered, with more discovered almost monthly. Around 150 have been named to science; the others must wait their turn. Until then, they receive a 'C' number, such as C-153, meaning the 153rd discovered that does not have a scientific name.

Corys are native to leaf-strewn streams of the Amazon basin, where they hunt aquatic worms, insect larvae and small crustaceans among the leaves. In the vast majority of the time their stream mates are Apistogramma species Cichlids and swarms of small, colorful tetras. Lurking predators like the Genus Crenicichla and in some waters, Hoplias, mean that both the Cichlids and the Corydoras key on the tetras. If the tetras are acting cool and unconcerned, so then are the Apistos and Corys. If the tetras scatter en masse, the Apistos and Corys take cover. That dynamic is a clue on what to keep with your Corys to see natural behavior.

For Corys to be at their best, keep them in groups, with the more you have the better and more entertaining they'll be. They are perfect for the planted aquarium as long as they have swimming room at the front, and they are perfectly peaceful fish.; even the smallest tetra species is safe with them. Corys all prefer soft neutral to acidic water, down to pH 6.5 or lower, but are adaptable; but don't go over 7.5 and moderate hardness if you wish to keep your Corys for years instead of weeks or months. Almost all the common Cory species are farmed, thus can adapt to different water parameters, but wild caught examples MUST have soft, acidic water to live, much less thrive.

As for feeding, Corydoras never met a worm they didn't like. Frozen or live, if they are suitable size, they'll very happily eat them, and do best if they have them. Small frozen shrimp, like Mysis, are good, as well as high-quality small sinking pellets. Mine adore frozen black mosquito larvae, and live California black worms.

Another clue is the leaves; Corys must have a softer substrate. Poor water circulation and sharp stone gravel can abrade whiskers, and since Corys use them to detect food, makes them crippled for life. Rounded pea gravel is OK, but make sure your tank is well filtered. It's strongly indicated that higher levels of Nitrate sink and hug the substrate, which most cory species spend the vast majority of their time, and can also lead to whisker degradation.

Thus sandy substrates are best, or even better, covered with suitable leaves. I use the original formulae of Eco-Complete with my Corys, as it's quite sandy. All of them look best over darker substrates, especially the lighter-colored species. All will be more richly colored on a dark substrate.

So, in a well-planted, well-filtered, soft water aquarium with tetras and dwarf Cichlids, Corys feel right at home. Many, many species are available, but you can keep them all just the same.

Now, some species.


Perhaps my favorite of the family is Corydoras guapore, of the Guapore River drainage in Brazil. I see them the most, as I have a dozen of them in the 75 to my right as I write this.

Topping out a shade over two inches, C. guapore is a very yellowish, brown-speckled bronze with a black blotch on the base of the tail, reaching up to the back of the adipose fin. The yellow bronze are on the top and bottom rays of the tail, which is otherwise clear, and on the lead rays of the other fins. Eyes are a silvery yellow. The snout is petite and points rather out, instead of down like most corys.

C. guapore spend a lot of their time up in the plants cruising the leaves for tidbits, and often rest on the leaves, even rolling over on them in their sleep. Sinking food brings them down. Agile little fellows, mine pursue live Daphnia with gusto, just as fast if not faster than the tetras do.

Since they are small, live, frozen and prepared must be suitably sized. A vegetable-based pellet is strongly recommended, as it intensifies their colors.

As they are quite small, very passive fish are the rule. Mine are tanked with Lemon and Rosy tetras, marbled Hatchet fish and a dwarf Ancistrus species. They have proven to be quite durable at 77 degrees, but from my research, that's the upper limit for this species.

In breeding, the school does it en masse and the vast majority of the eggs are on fine and broad-leaved plants. The fry grow rapidly on a diet of live microworms, followed by baby brine shrimp and sifted Daphnia. Mixing the microworms with small, pelleted foods toward the end of the time with the worms usually gets the little Corys to accept prepared foods.
A cooling, perhaps five degrees below tank temperature, twenty percent water change, when there's a thunderstorm in your area about half the time triggers breeding. Filtered rainwater is best for the partial change, but distilled or reverse osmosis water can work.

The school does very little roaming at night, and most of the time sleeps in the nooks and crannies of a large piece of driftwood in the tank.

A very cute, rather colorful little fish. May take you some time to find them, and they aren't cheap since they are still mostly wild caught and in demand, but well worth seeking out if you have a suitable tank for them.


The first Cory widespread in the hobby and first commercially bred is Corydoras aeneus, the Bronze Catfish of Trinidad; an island off the coast of Venezuela.

This fish was introduced freely into the US hobby in 1933, making it the grand potentiate Cory of the aquarium. Simply a green-yellow bronze on top and on the head, with a pinky-white lower half in it's native self, the Bronze Catfish has been around long enough several man-made variations have appeared. Most common is the albino form, where the fish is a pinkish white, and a long- finned form, which hinders the fish's ability to swim.

Wild caught examples are glittering little fish, though the more naturally-colored farmed form does shine a bit in the light when properly kept.

C. aeneus tops out at 3 inches, making it one of the larger species. They are very omnivorous, and will even eat soft algae if they find it while prowling the bottom realm. Thus, adding blanched fresh vegetables and fresh fruit will result in the best color and health for your fish. Frozen shrimp, insect larvae, worms, and live worms if available and clean, are very avidly eaten. Mine liked peach halves a lot.

Males are a touch smaller and slimmer than the females, which are wider when viewed from the top and visibly heavier-bodied than the males. Best temps for C. aeneus are 75 to 79 degrees. They do best in moderately soft water with a pH between 6.5 to 7.5.

Planted tanks with driftwood and stones are perfect for a group of Bronze Catfish. They hide somewhat under the bright light necessary for planted tanks, so floating plants over the swimming area are very helpful for proper viewing of this species.

In such tanks, Corydoras aeneus are almost ridiculously easy to breed. A cooling (perhaps five degrees below tank temperature) with filtered rainwater, distilled water or reverse osmosis water when a low pressure system is in your area will nearly always result in eggs all over your tank in the morning.

It's very worthwhile to home breed your fish, as the offspring will be healthier and much more colorful than the parents. In my culture manual section of foods for egg-laying fry, microworms are the perfect first food for your baby Corys. It's here (http://www.aquaticcommunity.com/aquariumforum/showthread.php?t=17459)

There are several variations in colors of wild C. aeneus, so keep your eyes out for them.

On to Part 2

07-04-2008, 06:50 AM
A stunning silver-white with black and yellow-orange accents is Corydoras adolfoi, of small black-water tributaries of the Rio Negro of Brazil.

The flanks of this two and a quarter-inch fish are a shiny silvery white. A mask of black is over the eyes, and behind it, is a bright orange stripe that changes to a lemon yellow as it goes down Adolfo's Cory. A broad black stripe starts at the dorsal fin on the back of the fish, and ends at the base of the tail. Fins are accented a bit with the silver-white, but are basically clear.

On a very dark, even black substrate, C. adolfoi has no equal in looks in the Corydoras clan. They are libel to blush unseen, unless you keep them with a large school of smaller tetras, like Neons. I keep 18 of these Corys with 12 dozen Hyphessobrycon heterorhabdus, as the red, gold and black stripe of the tetras complement the Corys' markedly, and keeps these little catfish in view all the time.

As much as all Corys like worms, C. adolfoi absolutely LOVES them. No Cory species I have work live Tubifex ensconced the substrate out to eat them the way a troupe of adolfoi can. They are very happy with any live worm you can culture; white, Grindal, small red worms, California black worms - adolfoi adore them all. Even frozen substitutes are avidly eaten, as well as Mysid shrimp, mosquito larvae - anything small, meaty, alive or frozen that's insect larvae or crustacean-based are optimal food for your group of adolfoi. Two or three different small pelleted foods can be part of their diet, but for optimum health, live and/or frozen foods must be a large part of the menu.

They really need a soft, slightly to moderately acidic planted tank to thrive. Driftwood will be a favorite haunt. Filtering through peat is helpful, since these are black water fish.

About a third of Corydoras adolfoi available in the hobby are farm bred in South America and Europe; the rest are wild caught. They aren't difficult to breed, as a cooling change as described in the breeding procedure for C. aeneus works for adolfoi, though they don't scatter eggs willy-nilly like aeneus does. In this species, the female adolfoi carries four or five fertilized eggs at a time with her anal fins, and very carefully sticks them to my bleheri species sword plant leaves. About 25 to 35 eggs are deposited.

As easy as they are to breed, raising the fry isn't. If you don't know how to or don't want to culture microworms, you'll have no hope of raising the fry.
The fry tank HAS to be soft and acid; pH 6.5 and hardness between 2 and 4 is optimal, and it HAS to be kept VERY clean. Fifty-percent water changes three to five times a day is not too much. The fry will take live microworms readily, but it's the next step in foods that's the problem; they won't eat prepared foods.

To my experience, kept with other Corydoras species fry usually gets the adolfoi fry to learn to eat small prepared foods, but not always. Having live baby brine shrimp and live small Daphnia on hand just in cause is vital.

Perhaps this species, as well as the C. guapore, are the most commercially viable Cory species to breed, as they are always in very high demand.


One of the cutest of the clan are Corydoras panda, the Panda Cory of small, leaf-strewn tributaries of the Pachitea and Ucayali River systems in Peru. For reasons only known by the scientist who named them, the Panda species name refers to the Chinese mammal.

This 2-inch catfish is a pinky orange with a mask of black over the eyes, black in the dorsal fin and a black blotch at the base of the tail. These are rotund little fellows; rather high bodied; a tiny chunk of cute Cory. Though they aren't inexpensive, Panda Corys in groups of more than a dozen are a very pleasant sight. They school together more tightly than any Cory species I've kept, save for the dwarf species.

The planted aquarium is ideal for your Panda Cory group. Though they will tolerate water up to pH 7.4 and very moderate hardness, they do best and are most disease resistant in the soft and acidic water; down to pH 6.0. Plants along the back and sides, allowing a good deal of swimming room in front, and with driftwood, is the best setup for these catfish. They will retire in the evenings to the plants and wood, as they would in their native waters. Temperatures between 72 and 77 are best. Dark sandy substrates really set off the colors of these Corys.

As they do come from mountain streams, one must keep dissolved Oxygen levels at no less that 8 mg/l for the Pandas' continual health. Given sympathetic surroundings and good, varied frozen, live and prepared foods, Pandas live more than five years. My group of 25 has been with me since early 2003 and are still going strong and still breed with vigor. They breed like other Corys; a cooling change when a thunderstorm nears the area.

I've found them very hardy in my pH 6.8 softwater planted tanks, and their color is outstanding with occasional live foods.


Perhaps the second-most common species of Corys after C. aeneus is Corydoras paleatus, the Peppered Cory of all over the Amazon Basin, and is also one of the largest, at nearly four inches long.

One of the two species available in a man-made albino form, the Peppered Cory is farmed in huge numbers in Asia and Florida. I'd strongly suggest getting your Peppered Corys that were bred in Florida farms, as the Asian examples have appeared over the last five or six years with a number of mysterious ailments that makes Peppered Corys die in a few days to a few weeks after introduction.

Healthy examples have pleasing grey and black markings on a pinky-silver ground. In exceptional fish, the dorsal sprouts to flowing magnificence in the males. As to feeding; the same as other Corys in this list, though the size of food sources will have to scale up as the fish grow. Live worms are of great benefit with Peppered Corys, as it tends to make them more active and vital.

Despite their adult size, Peppered Corys are just as fond of, and happy with, a group of their fellows as other Corys. A group of at least eight in a larger container, say a 75 gallon, is an endlessly entertaining show as they roll and tumble around.

On to Part 3

07-04-2008, 06:51 AM
Nearly bulletproof hardy when established, Peppered Corys prefer bright water with a near-neutral pH and moderately soft. They are ideal catfish for the large planted aquarium, as they are more in scale in such surroundings with their adult size, and seem to enjoy the tanks. Peppered Corys are adaptable, since they are commercially bred, but extremes in hardness and pH should be avoided. They do best in temps between 75-78, to my experience.

As an aside, none other than the famed Naturalist Charles Darwin himself discovered Peppered Corys during his voyage on the 'Beagle' in the 1830's.


By far the smallest Cory species are the two dwarves - Corydoras pygmaeus and C. habrosus - of Brazil and Columbia, respectively.

Both top out at just over an inch in total length, and their propensity to school en masse in the middle third of a tank caused them to be called 'Tetra Corys' for many decades. Being so small, tankmates must be chosen with great care, lest they be eaten. Small neon-tetra-size fish are ideal, but most barb species are out, save for Cherry Barbs, as they tend to pick on the little Corys.

Like all Corys, they prefer a soft substrate, driftwood and live plants. If you scatter clean Oak leaves on top of a layer of sand, these little Corys will breed almost constantly, and as the parents eat neither eggs nor fry, a tank can quickly become filled with fry, if the parents are the only fish in the tank. They also like to breed in Java fern.

It is vitally important to keep these Corys in as large a group as you can house, as they will slowly waste away if you keep them in numbers under 8.

You can feed them just like their larger cousins, but make sure the food is small enough for them to eat. Filtering though peat moss is recommended.


C. habrosus

C. habrosus does far better in tanks with soft, acidic water and temperatures not over 77 degrees, with 74 degrees optimal for this species. The pH can not be over 7.2. A steady, moderate linear current really helps this species, as they come from swift streams and are likely to be rather lethargic without the current. They look most attractive hanging all together in the current, especially when feeding on live food like Daphnia.

They look like miniature versions of C. paleatus; black and grey markings on a silvery pink ground. Bands of medium brown are on all unpaired fins. They are a touch larger than pygmaeus at 1.25 inches and spend more time on the substrate than that species does. They do, however, rise in a school together on occasion, usually when sinking food is in the offing.

Given sympathetic surroundings and varied, good food, C. habrosus are quite hardy, and rather charming in their manner.


C. pygmaeus

This species is smaller but just as hardy, if kept in the soft-water tank at 72 to 78 degrees.

Just a skosh over an inch in total length, C. pygmaeus are distinctive by the long, black line that bisects the fish. The back is a rather translucent olive, with amber overtones. Body is a light green, and a black line traces from the pectoral fins to the anal fin. Like the former, the head is small and the eyes large.

This species must be acclimated in a soft, acidic tank, say pH 6.5 and general hardness under 4. Given proper conditions, that is a planted aquaria with soft, slightly acid water, C. pygmaeus are deceptively hardy. Far more than the former, the Pygmy Cory spends a lot of time up in the lower water column, occasionally schooling with the small tetras one must keep them with. Pygmy Corys can take water up to 7.4 in pH, but it must be soft.

They breed as a school often, and raising the fry is a delight. They can take microworms right off, despite their tiny size, and will often feed off the sponge filter in the spawning tank. Vinegar eels and Rotifers are also excellent foods for your baby Pygmy Corys. They will join their parents' school when just half grown.


One of the more common species in shops is Corydoras trilineatus, which is also common in the streams in Peru, Brazil. Ecuador. and Columbia.

Since this fish is so common in nature, the majority available are still wild caught. Thus, inducing them to spawn is more difficult than other Corys. One must have patience for their Three-Line Corys to mature to their adult size of just over 2 inches before making an attempt to breed these fish. A cooling change as described above only works about a third of the time, and that's in their preferred soft, slightly acidic water. The fry aren't difficult to raise, but as this fish is common in shops, nothing is financially gained by breeding them except the sense of accomplishment by the fish keeper and a chance to add quality fish to the aquarium.

C. trilineatus is a silvery-bodied fish with reticulated black markings on the head, black stripes on the body broken up at the lateral line with a ragged black line. Concentric black stripes are on the tail and on the adipose and anal fins. A black blotch is on the top of the dorsal.

Despite being primarily wild caught, C. trilineatus are very hardy; nearly bulletproof. Frozen and live foods are best, with quality pelleted foods as another component of the menu. Plant-based frozen and prepared foods are recommended. Trilineatus can handle water down to pH 5.8 up to 7.2, and temps down to the mid 60's up to 77 degrees.

This fish is often confused with C. julii, especially since some trilineatus forms are spotted instead of striped. C. julii is smaller, about 1.5 inches, nearly white, and has hundreds of tiny brown dots all over its body, and its center stripe is dotted, brown, not black, and is shorter in length. They are also rarely imported, so if you see a fish identified as C. julii in shops, 9 times out of 10 the actual species C. trilineatus.


There are literally dozens of Corydoras catfish species that show up in shops, so keeping an eye out for the unique of these fish is a pleasant endeavor. All do best in the soft and slightly acid planted aquaria, but many are adaptable as long as extremes of pH and hardness are avoided. I encourage you to research the species you are interested in and consider a school of Corys for your next tank.


07-04-2008, 06:54 AM
Another amazingly awesome primer, Dave! Thanks so much!

07-04-2008, 06:56 AM
thanks again dave i enjoyed readingthumbs2: thumbs2: thumbs2:

Evil Slimy
07-04-2008, 09:03 AM
Great article. The only thing I would question is the substrates section. I'm not sure eco-complete would be fine enough for the cories to sift it through their gills and quite a few species do this regularly or bury their face in the sand. Their feeding behavior really changes drastically over small-grain sand.
Here's an example of what I mean:

07-04-2008, 09:23 AM
The original Eco-Complete of circa eight years ago was very, very sandy. The recent formulae is nothing like the original, as now days its quite corse. I also said that sandy substrates were best in the introductory section - sandy meaning sand, of course :)


07-04-2008, 12:49 PM
Bravo Dave! Another amazing primer!

07-04-2008, 02:45 PM
Great article.... Thanks for writing

07-04-2008, 03:38 PM
Great article, Dave!! I really enjoyed reading it. Aside from all of the great information, it's a really cool tidbit of knowledge that we're keeping a species of Corydora that was discovered by Darwin! :thumb:


Evil Slimy
07-04-2008, 05:21 PM
The original Eco-Complete of circa eight years ago was very, very sandy. The recent formulae is nothing like the original, as now days its quite corse.

Cool thanks. I didn't know it had changed so much. That was the missing info.
I think it should be part of the article though because I definitely wouldn't want anyone putting cories over the current eco-complete. At least the one I have is definitely very coarse and very sharp. Even CaribSea marks it as not burrower friendly.

07-04-2008, 09:52 PM
Great primer Dave!

07-04-2008, 11:40 PM
Great job, I really enjoyed reading it.

07-09-2008, 11:50 AM
Great primer Dave! Very well written, as always! thumbs2:

07-09-2008, 11:59 AM
Great info dave, thanks. :) Could you maybe put an addendum here and go into the issues with the Brochisgenus and how it fits into the picture. I know it is a hotly contested area among ichthyologists right now and the taxonomy is constantly changing.

07-09-2008, 12:47 PM
Thanks GB. I'll talk with Ian as the prevailing though is the Brochis Genus will be dissolved and the species will now be in the Corydoras Genus. But, will check with him and see anything is written in stone, yet.


07-09-2008, 12:52 PM
Sounds great. Thanks Dave. THe poor species of that genus have flopped back and forth, they're having a regular old Identity crisis.

07-09-2008, 01:04 PM
It's that 'clade' stuff again. I know science wants life forms in proper order based on like characteristics and genetic markers, but it's a pain in the rear when you write about fish for a living, and you have a sinking feeling that the scientific names will have changed yet again by the time the book is published.

Now if they try to move Scleromystax into the Corydoras Genus . . . .

Thankfully, the fish don't care what their Genus and Species is.


07-09-2008, 01:25 PM
Thankfully, the fish don't care what their Genus and Species is.

Quite true. LOL

08-12-2008, 03:22 AM
Thank you Dave for this article. It is very helpful. I currently have the smooth gravel in my tank. Is that a problem for them?

doug z
08-12-2008, 04:45 AM
Great article, Dave!

Maybe I'll get a dwarf cichlid, rather than dwarf gourami?

08-12-2008, 06:10 AM
Thank you Dave for this article. It is very helpful. I currently have the smooth gravel in my tank. Is that a problem for them?

Will be fine, as long as you have good circulation in your tank via filtration to help keep the substrate top fresh for the Corys, Torque.


mrs fishpatrick
09-23-2008, 08:58 PM
i enjoyed reading this, very usefull info thanks:19:

10-19-2008, 12:49 PM
Nice article~maybe you could post something about common illnesses particular to corys?

10-19-2008, 08:51 PM
Corys are susceptible to the same phalanx of diseases regular fish are. Keep in mind that fish diseases are almost always the fishkeeper's fault. The other is not being aware of the health of a fish you buy.


11-16-2008, 11:32 PM
Will different corys breed together?

01-11-2009, 04:14 PM
What about Albino corys?
I've had mine, 3 of them, for over a year now. But my ph is a natural 8.0 and they are doing great. They are great to watch and one of my favorites :)

01-11-2009, 04:40 PM
Outstanding primer Dave!
I have never seen it but yes Corys are capable of breeding with a different family of corys.I don't think it happens that often but they do mix.This conversation came up a while back.

doug z
01-11-2009, 07:00 PM
But my ph is a natural 8.0 and they are doing great.


8.0 pH is far from ideal, but sounds as if they've adapted admirably..

Goes to show that pH stability is more important than trying to adjust the pH of your tap water constantly to achieve a pH more suited to what the fish are genetically predisposed to..

But I would definitely get more than 3, Holbriter, if your tank's not fully stocked as is..

They love to be in groups of at least 6..

08-25-2009, 09:29 AM
you deserve an Honoris laurea in fishkeeping:22: !!! Can I ask u a question? Can I add a school of dwarf cories to my 135 litres ? Now I got only 1 betta male + 15 happy neons. and if answer is yes how many of them ? can they be introduced all in one go ? Water chemicals indicator are all ok, just in the average values, ph is around 7, and water is crystal clear , I mean no tannine and i suppose water is not particularly soft either.
again well done , bravo !

Catfish Hunter
12-19-2010, 05:04 AM
Terrific article! Thanks Dave.

I'm new here and new to keeping fish, but I have three trilineatus (thought they were julii until you got me to look into it a bit more). I'd like to add to this thread that I almost made a huge mistake today. Someone had recommended to me that aquarium salt can be good for fish so I bought some when I was out earlier. Luckily I did some research before I put it in, and learned what I'm sure most of you know: that salt can be extremely harmful to corys.

Anyway, thanks again for all your hard work.

03-13-2012, 07:32 PM
I have two salt-and-pepper cories, one julii (I think), and three pygmaeus. They're SO CUTE!:1luvu:

05-24-2012, 09:39 AM
This is brilliant! I had to run over to my tank after reading the Three-Line Cory section... Now I'm convinced that was I thought were Julii Cories are actually Three-Lines!

07-01-2012, 04:43 AM
Great... This article is just what I needed to read to help me prepare my aquarium for my school of Albino Cory.

-Robert P. Lewis

02-04-2013, 06:09 PM
Thanks for the info, Dave.

I have three (false?) Julii, one bigger than the others, in my 55 gal tank. I bought what I thought were the same corys but they turned out to be Serbai corys and I think these get bigger than the others. Not sure I want a 2.5-3" size cory in my aquarium. Will they intimidate the 2" corys? Take all the food? The LFS says I can exchange for the smaller version if I want, but I've gotten to kind of like these. They are pretty timid in the quarantine tank, though. They stay together all the time. Are you familiar with them?

I would also get at least two more false Julii to have a total of 7. Does this seem ok? I also have 3 Otos and would like to get about 3 more.....and I bought two more Kuhli loaches to have a total of 5 in the 55 gal. Is this too many bottom/scavenger feeders?

02-04-2013, 06:15 PM
sally, please start your own thread to ask your questions. Stickies are there for information, not for asking questions. Besides, Dave has not been on in nearly a year.