Not only are the Corydoras pygmaeus interesting fish to watch, but their small size, easy care requirements, and peaceful demeanor make them a good fish for beginners and experienced fishkeepers alike.
While there are a number of corydoras in the aquarium hobby, the pygmy cory is one of the smallest fish available; on average, the females typically reach a little over an inch in length and the males usually reach just under an inch long.
In their natural habitat, pygmy cories reside in a wide range of environments - small tributaries, creeks, pools, and areas of flooded forest. This variety makes them flexible with their aquarium setup, as long as extremes and sudden changes are avoided and regular water changes are performed.
Recommended water parameters are as follows:
pH: 6.2 - 7.4. They are flexible slightly outside of this range as long as sudden changes are avoided, but softer water is preferred.
Hardness: 2-15 dKH (but below 8 is perferable)
Tank Size: A minimum of 10 gallons is usually recommended, with tank length generally being more emphasized than height because these fish are fairly active. However, they will utilize all layers of the aquarium.
Pygmy cory cats prefer dim light since that's what mimics their natural environment. For this reason, it may be best to keep plants (if you choose to keep live plants) that can tolerate lower light levels, such as java fern, and/or to use floating plants that will cover the water's surface, such as frogbit.
Another thing to keep in mind is that the pygmy cory will occassionaly swim to the top of the tank and gulp a quick breath of air by using a labrynth organ, making it necessary for them to have a little access to air above the water line. However, a lid is highly advised as they are also known to be good jumpers.
It is often recommended to keep these either in a species only tank or with other small, peaceful fish. If kept with fish that are too large or aggressive, the pygmy cory cat may be outcompeted for food, or could possibly become food for some fish. Examples of good tankmates for the pygmy cory are neon tetras, cherry barbs, dwarf gouramis, and other fish of similar size and temperament.
Additionally, only sand or very fine gravel should be used as a substrate since they can be sensitive to gravel and potentially severe health problems could be caused over time.
And one last thing - water flow should remain gentle, as the pygmy cories are too small to fight off a hard current. Sponge filters are often the filter of choice with these fish, with some owners placing additional air stones in the tank.
When it comes to feeding, a varied diet will be the most beneficial. Though the pygmy cory is an omnivorous species, they tend to favor the carnivourous foods, in spite of the myth that they are primarily algae eaters. Brine shrimp, blood worms, and insect larvae are all welcomed food sources, as well as sinking pellets and wafers. At times, some people will add a little spinach or kale to the diet as well as blanched peas.
The mouths of pygmy cory cats are quite small, so you'll want to make sure the food is small enough for them to eat.
A healthy diet, along with regular aquarium maintenance, will not only help your fish be happy and healthy, but these things are also important factors when it comes to breeding. With these two conditions being met, they mate relatively easily on their own.
When breeding begins, one male will compete with other males (if multiple males are present) when a female is ready to breed. If you see two fish intertwined in a ""T"" position, they are breeding. The male will release his milt and the female will release an individual egg into her ventral fins. At this point, they will break the ""T"" formation. She will then clean a spot somewhere in the aquarium to deposit the eggs, with the male following along and keeping the other males away. They will rest there for a few minutes and may continue repeating this process a few more times.
Unlike some other fish species, once they lay all the eggs, their jobs are finished. The eggs hatch in approximately 3 days and the fry will look for plants in which to hide. Java moss is a great plant to use for this purpose; it's also very easy to maintain.
There is some conflicting information on whether the adults will try to eat the eggs and fry, so it up to the individual fishkeeper to choose what to do at this point. Because pygmy cories are somewhat carnivorous, it doesn't hurt to play it safe and remove the eggs or the place the adults in a different tank once the fish are done breeding.
You can remove the eggs and place them in a small container to hatch them. If you choose to do so, you will want to use an air stone to keep oxygen flowing in the water to help prevent fungus from forming on the eggs. If any eggs begin to show signs of fungus, they can be discarded. Alternatively, if using this method to hatch the eggs, you can use Methylene Blue, which is used in aquariums as an antifungal and antiparasitic disinfectant, and is commonly used to treat fish eggs to ensure they are not lost to fungal overgrowth. There are other products that can be used as well, such as Fritz Mardel Maracyn Oxy Remedy for Sick Fish.
Some cory cat breeders have reported that the adults don't bother the eggs or the fry, so you could also try your luck by just leaving the eggs alone and seeing what happens.
Fry appear as little black dots moving in the tank when they first hatch. The babies don't resemble the adults entirely, looking a little at first like tadpoles with barbels. Within 6 weeks, they typically will begin showing adult coloration.
A main concern with raising fry is feeding them; pygmy cory cat fry can be fed infusoria or crushed flakes (such as Hikari First Bites) until they are large enough to eat other fish foods. An easy way to grow your own infusoria (tiny organisms in the water) is to place a leaf of lettuce in the aquarium when the adult fish spawn. The leaf will decompose and produce infusoria in the process. After a week, replace that piece of lettuce with a new one to continue the infusoria presence in the tank. Repeat this process as long as necessary. Microworms or vinegar eels also are good feeders for both the adults and fry.
As the fry grow, you can also make a paste of egg yolk and water and place it near the fry. Later on, you may want to add crushed tubifex worms or flake food to their diet.
Overall, whether you try breeding them or not, the Corydoras pygmyaeus is an easy and fascinating species to observe. For your aquatic supply needs, feel free to visit Josh's Frogs aquatics page here.