Corydoras in Miniature

Fish Medication

Author: Mike Hellweg

An accomplished fishkeeper and breeder extraordinaire looks at the three dwarf/pygmy cories—Corydoras habrosus, C. hastatus, and C. pygmaeus—with notes on their proper care.

What’s Not to Like About Corydoras?

Corydoras catfishes are undoubtedly the most popular group of catfishes in the hobby and have been for decades. I don’t think there is a hobbyist out there who hasn’t kept them at one point or another. They are cute, and most are not at all shy. They go about their business without bothering any other fishes and are harmless to other community tank members. Most of them will even “wink” at you! This occurs after they dart to the surface and gulp a mouthful of air, which is actually part of their capacity to extract oxygen from the air. It is believed they are working the air down into their highly vascularized guts when they wink. To the hobbyist, this behavior just adds to their appeal.

Looking for Food

While they are often sold as “workers” or even “scavengers,” the truth is that they are just like any other members of your community tank and should be fed and treated as well as any other fish. That being said, they are constantly on the lookout for food and will poke into every nook and cranny searching for every morsel, but they won’t eat waste products or rotten food and they won’t make up for a hobbyist’s poor maintenance practices.

Group Travel

Most Corydoras are schooling fishes and should be kept in moderate to large groups of a half dozen or more. With many species, that means adding a lot of biomass to a tank, but with the three miniature cories we’re going to look at now a school of a dozen will add only a small amount to the total biomass of the tank, which won’t put much strain at all on the filtration system. While nano tanks and nano fishes have become very popular, these nano-Corydoras should be provided with a decent-sized tank and some room to move around and do what comes naturally.

Miniature Species

The three miniature Corydoras species are the checker cory (C. habrosus), the dwarf cory (C. hastatus), and the pygmy cory (C. pygmaeus). All are truly tiny, reaching maturity at just about an inch (2.5 cm) for females and about threequarters of an inch (19 mm) for males. A really large female may top an inch and an eighth (28 mm), but that’s about it. C. hastatus and C. pygmaeus are schooling fishes and spend the day exploring the mid-water level of the tank in a loose, evermoving group. C. habrosus individuals seem to like being in the company of just one or two conspecifics and can often be found poking about on their own. Unlike the other two species, C. habrosus spends most of its time on the bottom.

Clearing up the Confusion

Corydoras hastatus was the first of the three miniature cories known to science, having been described in the 1880s. It is a grayish brown fish with a large black caudal spot. There are two small but bright white spots in the caudal, one above and one below the black spot. Looking at some of the old literature from the 1920s to 1950s, you can see that what is often pictured is not C. hastatus but C. pygmaeus instead.

Corydoras pygmaeus was not described until the 1960s but apparently was being imported decades earlier. In the older literature pictures of C. pygmaeus were labeled as C. hastatus because that was the only miniature cory known at the time, and in old backlit black-and-white photos they do appear very similar. With the advent of color photography and better lighting, the photographic differences become clear. To this day, importers and wholesalers using older books to identify their fishes still often label C. pygmaeus as C. hastatus. I have ordered boxes of C. hastatus several times only to get a box of C. pygmaeus, and I know other dealers have had similar experiences. It’s not because our suppliers are trying to cheat us; it’s just that the old literature is still widely available. Fortunately, C. habrosus is very different in appearance, though I have seen some folks confuse C. habrosus with young C. paleatus.

Corydoras In the Aquarium

All three species are found in a variety of habitats from blackwater to whitewater over a fairly wide area from Venezuela and Colombia (C. habrosus) through Peru, Ecuador, and western Brazil (C. pygmaeus) to southern Brazil, Paraguay, and the Pantanal (C. hastatus); the habitats fluctuate widely over the wet and dry seasons. They are found mostly in gravel or sandy bottom areas, but also in the leaf litter of the flooded forests and over muddy bottoms in others. This means these diminutive Corydoras are very undemanding and adaptable. All three species like to move around a lot, so they need a large open area for swimming. They can be kept in smaller tanks, but they really shine in a 20-gallon (76-liter) long or larger tank. Plant the tank around the sides and back and add a large piece of driftwood or similar dÉcor to finish off the tank. I prefer using fine sand on the bottom.

Best Sand for Corydoras

Since Corydoras love to root about in the sand, often burying their face up to their eyeballs in search of tasty food morsels, I use oolitic or glacial sand that is almost rounded, with no sharp edges. Some types of construction and blasting sand have sharp edges to make them more appropriate for their specific tasks. Oolitic or glacial sand has been rounded by glacial activity, wave activity, or even by the activity of animals over millennia. It is often used by tile installers when mixing grout to avoid scratching porcelain tile. Be sure to find a type that is inert so it doesn’t cause the pH and hardness of the water to increase dramatically.

Finding Fish Friends

Any small mid-water or surface fishes can complete the scene. Small rasboras, danios, pencilfishes, hatchetfishes, and the blue-eye rainbowfish and lamp-eye killifish are all peaceful and perfect. Many small characins that are found in the same habitat as the Corydoras would do well, too. Serrapinnus kriegi (also found under its older names of Odontostilbe kriegi and Cheirodon kriegi), is not easy to find but is a similarly patterned small tetra that schools with Corydoras hastatus in the wild and is sometimes imported as by-catch in a group of wild-caught C. hastatus.

Spots

Interestingly, a grayish or silver body with a black-and-white spot pattern on the caudal peduncle similar to the C. hastatus pattern is often repeated in small characins found in the cory habitat. It is also found in the three-spot or Paraguay tetra (Aphyocharax paraguayensis) and in the featherfin tetra (Hemigrammus elachys).

Separation

As a side note, I would not suggest keeping the three-spot or Paraguay tetra with C. hastatus or any other small, peaceful fish for that matter. It appears to be a fin or scale eater and likely mixes in with schools of the other fishes to feed on them without causing a panic. Hemigrammus elachys has developed huge extensions on the fins, and I wonder whether these extensions are to serve as a distraction for these fin-predators.

Water Parameters

As would be expected for fishes with a diverse distribution, the miniature Corydoras do not seem to be too demanding when it comes to water parameters. They are equally happy in soft, acidic water and in harder, more basic and alkaline water. Instead of shooting for a specific number, it’s a better idea to try to keep dissolved solids under control by doing regular large water changes. I like to do a 50 percent or even larger water change at least once a week. In smaller breeding tanks I try to do water changes even more frequently, as the population can grow rather quickly. Temperature should be maintained in the low to mid 70s F (22º to 25ºC). Again, an exact number is not that important as long as the water doesn’t get too warm.

All three species seem to appreciate a decent current in the tank; while I use sponge filters, other hobbyists have had great success with canister and waterfall-type filters that create a much stronger flow in the tank. Whichever you choose, make sure to maintain it regularly as per the manufacturer’s instructions. The most fancy and expensive filter in the world will do no good if it becomes clogged and the water can’t flow through it. With most catfishes, lighting isn’t needed. In fact, some catfish hobbyists don’t even have lights over their tanks. It’s just the opposite with the miniature cories. They all seem to enjoy the light and are usually found out in the open all day long. At night all three species are found sitting quietly in small groups on the bottom.

Feeding

All three miniature cories will eat just about anything that fits into their mouths—commercial diets like flakes, wafers, and tablets; many smaller frozen foods like frozen baby brine, frozen copepods, and similar sized items; and small live foods. It’s a good idea to feed a variety instead of just a single food every day. I feed mine newly hatched brine shrimp, microworms of various types, Grindal worms, and young redworms. When conditioning them for spawning, I convert over

to almost 100 percent live foods. When just feeding a maintenance diet, they get flakes or pellets and baby brine or microworms very day.

Miniature Cory Breeding

The pygmy cory is the easiest of the three species to induce to spawn. The checker cory is almost as easy, while the dwarf cory is by far the most challenging. All three can be set up in pretty much the same way. I use a semi-permanent setup and move the breeders back to the main tank after fry and juvenile populations begin to get too large.

Selecting a Breeding Tank

My favorite tank for breeding the smaller cories is a 5½-gallon (21-liter) tank. I set it up with a mature sponge filter, a big mass of Java fern (Microsorum sp.), and a small amount of Java moss (Taxiphyllum sp.) attached to a piece of rock or driftwood. I cover the bottom with a thin layer of fine sand and add a pile of boiled or soaked oak leaves. The boiling or soaking is to make sure they sink. I then add a group of mature adults—fish that are at least 10 to 12 months old. It’s a good idea to add more males than females to the tank, something like two or three females and up to six males. Initially I’ll start out with water from the main tank, but as I do each water change I’ll start adding more and more soft, acidic water to the tank. Again, I’m not looking for a specific number. What I’m doing is simulating the start of the rainy season by adding softer, more acidic water to the tank.

Proper Water Conditions

Spawning time is the only time when the water parameters become important. I’ve found that using softer, more acidic water with a low alkalinity results in fewer infertile eggs. That being said, since they are so adaptable, in many parts of the USA the miniature cories will spawn successfully without any modification of the water at all.

If you have really hard, alkaline water you might be best off adding reverse osmosis (R/O) water. If you don’t want to buy an R/O unit, you can buy R/O water at most grocery stores as well as many better pet stores. As you do water changes, add mostly R/O water with just a small amount of dechlorinated tap water mixed in. I would shoot for about a cup of tap water to a gallon of R/O water. This will add some minerals and some buffering capacity (alkalinity) so the pH doesn’t suddenly crash and stress or kill the fish. Adding peat extract to the water also seems to help prevent unfertilized eggs from becoming covered in fungus, which can spread to and kill healthy eggs. I feed the breeders heavily with live foods as described earlier, sometimes three or four times a day. While the fish will often spawn with no further intervention on the part of the hobbyist, the best time to try for a spawn is when a storm front is coming through. There is plenty of anecdotal evidence that the sudden change in barometric pressure is a trigger for spawning in many Corydoras species, including the miniatures. I’ve tried it. It works every time.

The day before the storm is forecast, I’ll do a very large water change. Many hobbyists use water that is up to 10ºF (5.5ºC) cooler than the regular tank water, but I’ve found that to be unnecessary unless the fish are regularly kept at high temperatures. As long as temps are in the low to mid 70s F (22º to 25ºC), there isn’t a need to lower the temperature further.

The next thing I do to get the fish ready is add two or three airstones to the water, bubbling away at full strength. So you have well-fed, sexually mature fish, relatively cool water, large changes towards softer and more acidic water to simulate rain water, simulation of stormy flow by adding the airstones, and finally a change in barometric pressure. It’s like putting on a Barry White album for them. They almost invariably will spawn.

Spawning

Spawning begins with a chase. The males will chase each other and the females, jockeying for position. Eventually one male will win out and begin to mate with the most ready female, which is also usually the largest. Over the next hour or so they will mate several times, with a single egg or a couple of eggs lain after each spawning event. Sometimes another pair will form up and start spawning simultaneously with the first pair. The “T” position has been well described elsewhere, so the only thing I’ll note here is that both C. pygmaeus and C. habrosus generally do this on a surface (the glass, the bottom, etc.), whereas C. hastatus generally forms the “T” position in mid water.

Adhesive eggs are placed in small clusters on the glass, on the filter, or in the plants. As long as they are well fed, none of the miniature cories will show any interest in the eggs or the resulting fry after spawning. The eggs hatch in about four days, and the fry swim free about four or five days later. They will eat the same foods as the adults—newly hatched brine shrimp, microworms, and finely crushed flakes. In addition, many hobbyists feed them “sponge grunge,” which is gathered by squeezing sponge filters from a healthy tank into a container. The resulting brown gunk is allowed to settle, and the water just above the gunk is collected and poured into the tank. It is full of rotifers, ciliates, and other microscopic critters that the fry will gorge upon. Some hobbyists just squeeze the filter into the tank, but I think that just adds a lot of waste material along with the good stuff. Being patient and allowing the gunk to settle out doesn’t take that long and is much safer for the fry.

Fry

Young cories grow quickly and will reach half an inch (13 mm) in just six to eight weeks. Feed them two to three times a day, and change at least half of the water two or three times a week. If you’ve finished with spawning the parents and you’ve had to modify the water, start adding back regular tap water in larger and larger percentages to the R/O water with each change until you’re back at full tap water.

If you want the adults to continue spawning, keep adding the special breeding R/O water mix. Since well-fed adults don’t prey upon their progeny, it is a good idea to thin out the breeding tank regularly. I generally move the adults back to the main tank or to another spawning tank after three weeks of spawning. That generally results in several dozen to several hundred fry, depending on the age and size of the spawning adults.

Meet the Minis

C. habrosus is called the checker cory and is sometimes called the dainty cory. I’m not sure why, as dainty usually means “delicate and pretty.” Checker cories definitely are cute, but they are not delicate. They are almost bulletproof. They are less active schoolers than the other two species. They prefer spending more time foraging on the bottom on their own or in small, loose groups. There is a similar but slightly larger species that is sometimes sold as the checker cory (C. cochui). I have not seen that fish for sale in many years, but since it was common at one time, it is possible it will be available again. Its care and breeding is very similar to that of C. habrosus.

C. hastatus is known as the dwarf cory. It is most often found in mid water and often schools with small characins in the wild. Individuals will feed at mid-water levels, chasing down daphnia and small brine shrimp. They are more challenging to spawn, requiring softer, more acidic water. Their fry seem to be more delicate and slow-growing and are a bit more challenging to raise than the other miniatures. Added to that, they are not often available in the trade and are much more expensive when they are available.

C. pygmaeus, appropriately enough, gets billed as the pygmy cory. The species is easy to care for and easy to induce to spawn. Pygmy cories are often the first Corydoras species that many breeders have success with. They are awesome schooling fish and will form tight groups of up to several dozen individuals as they forage around the tank. They swim near the bottom of the tank and in mid water for short bursts of time. A friend of mine has a 75-gallon (284-liter) tank with about 200 pygmies in it. It is one of the coolest tanks to watch that I have ever seen.

If you are looking for fish that have a unique charm and are fascinating to watch, give a group of one of the miniature cories a try. Even though they are small and will do well in nano tanks, give them something more like a 20-gallon (76-liter) tank and sit back and enjoy the show. After all, isn’t watching fishes the reason we all got into the hobby in the first place?