Minimum Tank Size: 20 Gallons (75 Liters)
Care Level: Moderately Difficult
Water Conditions: PH 5-5-7.5 Soft to Moderately Hard
Temperature: 68-79°F (20-26°C)
Maximum Size: 2 inches (5 cm)
The Corydoras julii, also known as the julii cory, is one of the most sought-after species of corydoras catfish in the hobby – but tend to be relatively rare in stores. And even when stores claim to have these fish, they are usually other species of corydoras catfish that have been misidentified (like the leopard cory or the three-stripe cory).
Corydoras julii are native to the Amazon River, the coastal rivers of eastern Brazil, and can also be found in Peru. They inhabit small streams, swamps, ponds, and the floodplain forests during the rainy season.
Corydoras julii rank among the smaller of the corydoras catfish and only grow to a maximum length of 2.5 inches (6.4 cm) in the home aquarium. These fish usually live between three to four years in captivity, though it’s not uncommon for some to live as long as ten years.
While these fish can be difficult to find, their stunning coloration makes it worth the search. They are easily among the most attractive of the corydoras catfish, and it’s their unique coloration that allows them to be distinguished from the imposter ‘julii corys’ sold in stores. Real Corydoras julii will have a small spotting pattern and a black mark on their dorsal fin.
Like most other corydoras catfish, these fish are peaceful and make excellent additions to most community tanks. They should always be kept in shoals of at least six, but tend to only thrive in larger groups. While they aren’t particularly demanding, they should always be kept in a fully cycled 20 gallon aquarium (Read The Complete Guide to Cycling an Aquarium).
One of the key ingredients to keeping corydoras catfish happy is to provide them with a non-abrasive substrate that they can easily root through. In the wild, they continuously forage for food, and even when well fed, they will still root in the substrate of an aquarium. If the substrate is abrasive or sharp, it can damage their sensitive barbels. Play sand or aquarium sand are both excellent choices for a substrate, and while not ideal, aquarium grade gravel is also acceptable.
While these fish don’t necessarily require a planted tank, they should still be provided with cover to give them a sense of security. Aquatic plants fill this function quite well, while also having the added benefit of helping to maintain the aquarium water. Ornaments and caves should also be provided, especially if a fish tank is brightly lit.
Any tank containing Corydoras julii should be well-filtered, and a hang-on-back filter is usually more than sufficient. When it comes to choosing a filter, I highly recommend an Aquaclear Power Filter. I have these filters on nearly all my tanks, and they are surprisingly rugged. They have all been running problem free for years, and they go through some really hard use on my fish tanks.
While these fish are constantly on the hunt for food, it’s important to feed them directly when they are kept in a community tank. If they aren’t provided with food specifically for them, their tankmates will often devour all the food before any can reach the corys. In order to make sure the corydoras get fed, I recommend giving them a sinking food like Hikari Tropical Sinking Wafers.
But for them to remain truly healthy, they should be fed a varied diet, and both live and frozen foods should be offered. Blackworms (or Tubifex in Europe) are an excellent choice, and when it comes to frozen foods, bloodworms, daphnia, and brine shrimp are all greedily accepted.
These fish are relatively easy to breed and will often mate on their own if both males and females are kept together. Unfortunately, the fish usually eat their own eggs, so to reliably breed them, a breeding tank should be setup. But prior to setting up a breeding tank, the fish must be sexed. The females are usually rounder than the males, with larger, deeper bodies.
To start with, two males and one female should be placed in a breeding tank. The breeding tank should be heavily planted, with a thin substrate along the bottom. While most breeding tanks avoid a substrate so the tank can be easily cleaned, evidence suggests a substrate aids in fry survival with Corydoras julii.
After a breeding tank is setup and cycled, the male and the female should be conditioned with live and frozen foods for a least a week, until the female is noticeably heavy with eggs. Once the female is egg-laden, a large water change (greater than 50%) should be completed, with the new water being slightly cooler than the tank water. This simulates the yearly rains and normally should trigger breeding. If no breeding occurs, then repeat the water changes until the fish mate.
After a successful mating, the female will lay sticky eggs on the plants, substrate, and sometimes even on the aquarium glass. Once the eggs have been laid, the catfish should be removed from the tank. Alternatively, the eggs can be removed, but this is difficult unless specialized spawning mops were added to the tank.
If the eggs are moved to a new aquarium, then the new fish tank must be fully cycled. Some people recommend using water from the breeding tank to skip this step, but it’s usually a good idea to provide a fully cycled tank instead.
The fry will usually become free swimming after 3-4 days and can be fed commercial fry food, or baby brine shrimp and microworms.
Quirks and Handling Instructions
It’s perfectly normal for corydoras catfish to take breaths of air from the top of the aquarium. They are adapted to survive in low oxygen environments and can draw air into their mouths and absorb it through their intestines. They will do this even in well-oxygenated aquariums, so there’s no need to be concerned if you observe this behavior.
When handling these fish, care should be taken since they have pectoral-fin spines that can easily pierce human skin and deliver a nasty and painful sting. It usually only takes getting stung once to learn to avoid it, but care should also be taken when using nets with these fish, as the spines can get tangled in the mesh. A good way to capture these fish without the use of a net is to use a cup instead.