Julii Cory Catfish Care: An Expert’s Guide

The Julii cory catfish or Corydoras julii is a peaceful, beautiful, and relatively easy to care for fish. In this guide, you’ll learn about the confusing background of this species and how to take care of this unique cory catfish.

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Quick overview

Wild habitat	North-East Brazil, small rivers and streams
Size	<2 inches (5cm) Females get up to 0.2 inches bigger than males.
Temperament	Calm, peaceful
Tank Size	>20 gallons (75 liters)
Diet	Carnivorous, feed a variety of sinking pellets and live/frozen foods
Water	73-79°F (23-26°C) pH: 6.0-7.5
Difficulty	Some experience needed
Etymology	‘Cory’: Derived from the Greek word ‘Korus’, meaning helmet ‘dora’: meaning skin. ‘julii’: a mysterious identity

About the author: Thijs is an aquarium enthusiast that writes at his blog KeepingCatfish.com, where he writes on the care of aquarium catfish such as cory catfish and pleco catfish. He is also the writer at one of his hobby projects, Wild Betta Blog where he promotes the little known wild betta fish.

In the wild

This cory catfish species can be found in North-East Brazil, in the province of Piauí. Corydoras julii inhabits small to medium-sized rivers, with a sand-gravel substrate.

Their light skin color and dots camouflage them perfectly in these habitats. Their nickname ‘Leopard cory’ also comes from this unique pattern.

They live in shoals that range from a couple of specimens to hundreds or even thousands of fish as a way to protect themselves from predators.

Appearance

Corydoras julii is easily distinguishable by the spots all over its body. It has a mid-body stripe that reaches around halfway across the body. The Julii cory catfish reaches around 2 inches full length, males stay smaller than females.

The dorsal fin of Corydoras julii is transparent, with a black dot covering around ½ of it.

Julii Cory catfish are part of the armored catfish genus (Corydoras). These fish got their name because they don’t have scales, but armored plates across their body.

Corydoras julii vs Corydoras trilineatus.

If you’re reading this article, chances are you don’t actually have Corydoras julii in your tank, but Corydoras trilineatus or the three-stripe cory catfish. These two fish are very similar, especially for starting hobbyists. Another nickname hobbyists like to give to C. trilineatus is the ‘False julii cory catfish’, because of this confusion.

There are some clear differences between both species though:

Midbody stripe – C. trilineatus, also called the three-lined cory, has a clearly visible black line that covers the entire body length up to the tail base. In the case of C. julii, this line is shorter and paler.

Spot pattern – Corydoras julii didn’t steal its name ‘the leopard cory’. As opposed to C. trilineatus, C. julii has more, usually smaller, distinct spots across its body. Around the head area, these spots become more present and brighter. The three-lined cory on the other hand shows a more reticulated net-like pattern.

Size – C. julii stays smaller than the C. trilineatus, getting respectively 2 inches and 2.5 inches.

Pet stores often use the name ‘Julii cory catfish’ to sell Corydoras trilineatus, because this sells better. The real julii cory catfish is thus actually a very rare sight in the hobby because it isn’t bred that often and is rarely collected.

On top of that, Corydoras julii species can be crossbred with Corydoras trilineatus, since they are both parts of lineage 9. This unfortunately decreases the pool of pure Corydoras julii, which brings even more confusion into the hobby.

Tank

The Julii cory catfish has similar requirements to other cory catfish in terms of tank requirements.

Most cory catfish species need a tank that’s at least 20 gallons, including C. julii. Only a select few small cory catfish like pygmy cory catfish can live in a 10-gallon tank.

Filtration

Since cory catfish don’t produce a lot of waste themselves, the recommended filtration depends on the tank mates you want to keep with your cory catfish.

If you decide to set up a dedicated breeding tank, a sponge filter is one of the best choices: it filters biologically, it’s cheap and low-tech.

If you keep them with a lot of other fish or big polluters like pleco catfish, a stronger filter is recommended. I recommend a filter that does a minimum of 6x the volume of the tank per hour.

Plants and decoration

Live plants are a great addition and I’d almost say a necessity for your cory catfish. They drastically improve the water quality and provide natural cover for your fish. What species you use doesn’t matter, but you can read the guide on beginner aquarium plants for more.

Wild-caught cory catfish are known to prefer live plants over glass or spawning mobs, and sometimes they only deposit their eggs on these plants.

If you want to know more about the best plants for cory catfish, there’s a full guide on this blog about it. You can read it here.

Substrate

We’ve arrived at a quite controversial part of keeping cory catfish: picking a gravel kind.

The best gravel kind for cory catfish is sand, but a rounded gravel kind is fine, too. The reason for this is that cory catfish have sensitive barbels that can be damaged by sharp gravel.

Although it might look like nothing, in the beginning, continuous exposure causes micro erosions that eventually cause the barbels to die off.

These barbels are crucial for finding food and if your cory catfish doesn’t have them, this can cause diseases and possibly even death.

Where’s the controversy, you ask? Well, some experts have pointed out, including Cory from Aquarium Co-Op, that cory catfish have been known to live in habitats with sharp gravel. This substrate consists of a mixture of sand, stones, and sharper pebbles.

Although this might be the case in some wild habitats, it’s still a far safer choice to pick a rounded or sand substrate. After all, this has the lowest possible risk of harming the barbels.

If you do use sharper gravel, don’t feed food that falls into pieces fast or gets into the gravel easily. This food will cause the cory catfish to have to dig into the substrate. The same goes for most live foods, as larvae like bloodworms will dig into the substrate.

Although sharp gravel can have a negative effect on the barbels, bad water quality and bacterial infections in the substrate are also a big reason why cory catfish barbels erode. Regularly cleaning the filter and performing regular water changes are thus a must.

Tank mates

Overall, Julii cory catfish is a very peaceful fish species that can live with a lot of other fish. C. julii doesn’t do well with overly competitive species like cichlids or barb species. Even though it can certainly be done with some preparation, it’s not recommended for beginners.

Here are some examples of suitable tank mates for cory catfish:

Betta fish
Shrimp
Snails
Tetras
Rasboras

Cory catfish should always be housed in groups of the same species. This means that Corydoras julii should always be housed in a group of 6 or more fish. Otherwise, these fish get stressed and will not show their full potential.

Mixing cory catfish is possible, but then the same rule goes: keep at least 6 specimens of the same species. Another thing to look out for is interbreeding. Julii cory catfish can interbreed with other species of lineage 9, so avoid putting these species with Corydoras julii.

Water parameters

Most cory catfish are pretty tolerant in terms of water parameters and they can live in a wide variety of conditions. The Julii cory catfish is also not picky when it comes to water parameters, although it does prefer slightly acidic water.

The ideal water temperature for Julii cory catfish is 73-79°F (23-26°C), unlike some cory catfish that don’t need a heater this species certainly does. Julii cory catfish do well in a pH of 6-7.5. The ideal GH and KH values are between 4-8, but softer water is more similar to their natural environment

Wild-caught Corydoras julii tend to be more sensitive towards water parameters and like a lower pH (more acidic) and overall softer water. This can be achieved by adding RO water or (well-filtered) rainwater. Another natural alternative are Indian almond leaves, which add a natural touch to your aquarium.

Diet

It’s important to note that cory catfish don’t eat algae and can’t survive on only leftovers from other fish. Since they are not competitive and can only eat food that’s on the bottom, all the other fish will eat the food before they get a chance.

Julii cory catfish are omnivorous fish, but they do best on a high-protein diet. In the wild, they eat a variety of insect larvae, worms, and other small invertebrates.

Cory catfish should be fed their own diet, preferably a varied diet consisting of different pellets. Cory catfish also love live foods such as bloodworms, blackworms and mosquito larvae.

Because not everyone has access to live foods, a great alternative are Hikari pellets. I’ve found Hikari Carnivore Pellets and Hikari Sinking Wafers to be great. I also love Repashy foods. Additionally, you can feed some algae wafers or spirulina wafers to feed them some extra nutrients.

Breeding

Breeding Corydoras julii is similar to breeding other cory catfish species. Breeding cory catfish can usually be split into three phases:

Conditioning
Simulating the dry season
Simulating the rainy season

Sexing julii cory catfish

Female Corydoras julii are fuller and plumper than males. They also tend to be a little bigger. Especially after conditioning these fish well, you will be able to clearly see a difference (if your cory catfish have reached maturity, at around 9 months of age).

The ideal ratio for breeding Julii cory catfish is one female to two males because this increases the chances of fertilization.

It’s important to know that it highly depends on the specimens, your water parameters, and many other conditions on whether cory catfish spawn. Having success with breeding can be either very easy or require extensive efforts, sometimes unexplainable.

However, in most cases breeding Corydoras julii is fairly simple with this three-step process. You can take this process as far as you want, depending on how easy your cory catfish breed.

Conditioning Julii cory catfish

During two-three weeks, you should increase feeding and switch to live foods (or frozen foods if you can’t find this). Preferably feed small portions two to three times a day. Good live foods are blackworms, bloodworms, grindal worms, and mosquito larvae.

During this time, the goal is to make the female gain weight and produce eggs. This extra food will bring incentivize breeding behavior and start the natural breeding cycle.

Simulating the dry season

This is the season in the Amazon where food becomes scarce and the temperature rises. The water levels also drop and cory catfish go into “survival” mode.

You can simulate this on a small scale by increasing the water temperature by a few degrees (gradually, don’t boil your fish!) and lowering the water level of your tank to 50%.

I recommend doing this for three to seven days. Stagnate or decrease feeding during this time for optimal results.

Simulating the rainy season

In this season cory catfish naturally spawn. Fresh and cooler water flows into the rivers with heavy rainfall filling up the streams, while more food is available.

This can be recreated on a small scale by filling back up the tank of your aquarium with slightly cooler water. If this isn’t enough, you can keep changing the aquarium water

If your breeding attempt has been successful, you will see the cory catfish depositing their eggs against the glass. Place the eggs in a separate container for optimal success rate. After this, the fry can be fed baby brine shrimp.