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Spawning Corydoras Catfishes

Hello, Frank Indiviglio here. Among the 150+ species of catfish classified in the genus Corydoras, all native to Central and South America, we find some of the most beloved of all aquarium fishes. Yet despite their willingness to breed in captivity, not many aquarists make the effort. As we will see, however, the droll cory cats employ one of the fish world’s most unusual breeding strategies…they are definitely worth a closer look!

Startling Reproductive Behavior

Female cory cats are larger than males, and their body has a thicker, more rounded appearance. In some species, the male’s dorsal fin is thinner and higher than the female’s and is held in a noticeably more erect position.

Bronze CoryCorys may breed in either pair or group situations. Males chase gravid females, with the pair eventually lying motionless and perpendicular to one another (this is known to aquarists as the ‘T-Position”). The male lies on his side, and, amazingly, the female then uses her mouth to withdraw sperm from his vent.

Fertilization – Internal or External?

How fertilization actually occurs is still open to some discussion. Most ichthyologists believe that the sperm exits the female’s gills, and is shunted to a unique cup that she forms with her pelvic fins.

Upon obtaining the sperm, the female lays 1-5 eggs into this cup. She then moves off to a pre-cleaned site, usually a plant or the aquarium glass, where she glues each egg individually. She repeats this process with the same or another male until her clutch of 10-25 eggs is laid, an ordeal that may last 3-6 hours.

Some researchers have suggested that the sperm passes through the female’s digestive tract, to be released along with the eggs, or that the female expels the retained sperm upon the eggs. In any event, a most extraordinary means of fertilization…why such a strategy would evolve has not, to my knowledge, been explained.

Breeding Corydoras

While Corydoras cats may spawn spontaneously, the most consistent results will be obtained if cool, highly oxygenated water is added to the aquarium, simulating the drop in temperature and rise in water levels that accompanies the start of the rainy season in most Corydoras habitat. Dropping the aquarium’s water level beforehand may also help.

While various species differ in their requirements, the formula that I have used for bronze corys (C. aeneus) seems to work well in general. After dropping the water level for 2-3 weeks and maintaining it at 76 F, I add water of 60 F in an amount equal to 1/3 the volume of the tank.

Caring for Eggs and Fry

The eggs can be left in place and the adults removed (some are egg predators), or they can be carefully transferred to a rearing aquarium (they are fairly large and sticky for a day or so after deposition).

The fry should be housed in shallow water (3-4 inches) at first, as constantly rising to the surface for air will weaken them significantly.

Cory cats are, despite their “scavenger” reputation, highly specialized predators on tiny invertebrates. Their fry are best reared on live blackworms, brine shrimp and Daphnia, with animal-based flakes and pellets being added as they grow.

Plan to be in it for the long haul…a bronze cory in my collection is nearing 21 years of age!

Further Reading

Panda CoryPeru’s popular panda cory (Corydoras panda), described in 1969, favors cool, fast moving streams. To read more, please see


Please write in with your questions and comments. Thanks, until next time, Frank Indiviglio.

About Frank Indiviglio

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Being born with a deep interest in animals might seem unfortunate for a native Bronxite , but my family encouraged my interest and the menagerie that sprung from it. Jobs with pet stores and importers had me caring for a fantastic assortment of reptiles and amphibians. After a detour as a lawyer, I was hired as a Bronx Zoo animal keeper and was soon caring for gharials, goliath frogs, king cobras and everything in-between. Research has taken me in pursuit of anacondas, Orinoco crocodiles and other animals in locales ranging from Venezuela’s llanos to Tortuguero’s beaches. Now, after 20+ years with the Bronx Zoo, I am a consultant for several zoos and museums. I have spent time in Japan, and often exchange ideas with zoologists there. I have written books on salamanders, geckos and other “herps”, discussed reptile-keeping on television and presented papers at conferences. A Master’s Degree in biology has led to teaching opportunities. My work puts me in contact with thousands of hobbyists keeping an array of pets. Without fail, I have learned much from them and hope, dear readers, that you will be generous in sharing your thoughts on this blog and web site. For a complete biography of my experience click here.