Breeding cories is in general fairly easy, and these are probably the easiest of cories to breed and raise.
While the parents of some members of this team had to make due with a 20 high, these fellows are set up in a 55, heavily planted, some driftwood. Over the lat two years, they have shared space with a breeding pair of Ancistrus; Black Neon, Flame (Von Rio), Glowlight, Black, and Diamond tetras; a pair of Laetacara curviceps, some young Festivms, some lesbian Angelfish (an amusing story for some other time), Siamese Algae Eaters, Otocinculus, and two other species of cories (C. metae and C. sterbae). Currently, the tank population is 6 C. aeneus, 2 Ancistrus, 4 High Finned Black tetra, 6 Diamond Tetras, and 1 Siamese Algae eater (making good inroads on a serious Black Brush Algae outbreak). The substrate is partitioned into two zones of mixed fluorite, black gravel, and ecocomplete, well mixed, to the rear right and left, and a long strip of sand across the front and extending to the back just off center. There is a largish piece of driftwood covered in Java Fern arcing over the sand toward the back forming a low cave (which the male Ancistrus has claimed for his own), and another branchy driftwood covered in Java Moss. There are Radicans, Amazon, and Uruguay swords and a grove of rooted Water Sprite. Light is a pair of 48" fluorescents on 12 hours daily. Heat is provided by a pair of 75 watt heaters, maintaining 75° in the winter, about 80° in the summer. There is an Eheim 2215 generateing a current the length of the tank, and an Emperor 400 creating a transverse current at the far end. I do not service these anywhere near enough. The tank gets bi-weekly 50% water change, direct from the tap. I am told that my water is quite hard and alkaline, however, the water treatment regimen that I use (Amquel+ and NovAqua+, pond concentration, added directly to the tank as the water is pumped in from the tap) drops nearly all of the hardness out and crashes the pH to about 6.8. I aim to have the change water about 10° cooler than the tank water, as this is a nigh unto irresistible spawning trigger (particularly if done in conjunction with a cold front and the consequent air pressure drop).
The breeding team consists of 2 females and 4 males. One of the females is one of the original fish as is one of the males. One of the females was purchased, as was one of the males. The remaining males are the what is left of my initial spawn (I sold the rest).
In order to condition this tank for breeding (and it also induced the Diamond tetras to spawn), I followed a regimen of daily feedings: 3 days dry (including 3 flakes, 2 pellets, and 2 tablets, one algae); 2 days frozen (bloodworms, spirulina brine, freshwater frenzy, krill, daphnia), one day live (Brine shrimp and Blackworms), and one day of fasting. While preparing them for breeding, water changes were weekly, about 30%. The cories reliably spawned after ever other water change.
When spawning, the female rockets around the tank in arcs, hotly pursued by one or more of the males. Ever so often, she will pause on the sand and one of the males will position himself at right angles to her with his vent directly in front of her mouth. This is the classic Cory "T" position. It has been theorize that he discharges his milt into her mouth and it then passes through her digestive tract and out her vent onto her eggs. There are some flaws with the research leading to this conclusion, but I like to believe it. It's suitably filthy. Regardless, she then clamps her ventral fins together and into the pocket formed lays a number of eggs, usually around a half dozen. She then swims off to a suitable surface (a tank wall, a swordplant or java fern leaf, a filter intake, a heater), cleans it with her mouth, and sticks the eggs to it. The process is then repeated until she is spent. With two large females, the tank looks spackled afterwards, with perhaps 2 or 3 hundred or more eggs laid in large sprays.
For the original spawn, I had removed a number of java fern leaves to a sand bottomed 10 gallon tank. I had fungus problems. The 10 gallon tank still figures in this though. I took 50 or so eggs, scraping them from the tank walls with a credit card, and put them in a pint betta cup, which I then placed on the middle shelf of my fishroom stand where it is reliably 82°. Into this I put the recommended dosage of Betta Fix (a dilute methylene blue solution). (For the subsequent spawn, I put the eggs into a livebearer breeding trap in the grow out tank, described below, and added enough betta fix for 5 gallons to the trap). I did not have any fungus problems this time, though the eggs slowly turned milky over the course of a few days (predictable with albino embryos inside). The eggs hatched on the third and fourth day, at which time I dumped the fry into the grow out tank.
For growing out the fry, I used a tank in which I was also growing out spawns of Corydoras metae and Rineloricaria eigenmanni (see the spawning summaries thereof), and fed the entire tank the same regimen. Briefly: 10 gallons, thin sand substrate, lots of Java Moss, floating cover (Pennywort then Water Sprite) , Hydro1 Sponge Filter set medium high, 50 watt HOB heater, set to 78, but unplugged as the lights in the fishroom bring the temperature up to 90° on the top shelf in the summer. Twice daily feedings: frozen baby brine/Cyclops/rotifer mix, cyclopeze powder, brine shrimp pellets, and spirulina tablets. Weekly water change with aged water, medium soft, pH around 6.8. Cory fry larger than a half inch are moved to various other tanks to complete their growout.
What's to say? If you treat them well and feed them right, they will spawn if you change the water regularly with cooler water. This was an excellent learning experience for getting a handle on breeding egg laying fish.
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