THE COOL CORY OF ARGENTINA
We usually associate Corydoras with warm and acidic waters. Here’s a species that likes things cooler and more alkaline.
We usually associate Corydoras with soft and acidic, tropical waters. Cory expert Ian Fuller introduces and breeds a species that likes things cooler and more alkaline.
CORYDORAS MICRACANTHUS is a relatively small species growing to between 36mm and 38mm (standard length/SL) for adult females, with males a little less at 32 to 34mm. The species comes from the Salta and Jujuy provinces of north western Argentina. The original type specimens were collected from the Rio Mojotoro basin, but the catfish is known to have a wider distribution, which extends to the Rio Grande, Rio Colorado, Rio Blanco and Rio Pescada and its tributaries, all part of the upper Rio Bermejo drainage.
Across these, it inhabits clear and shallow, slow-flowing and algaecovered rocky streams, with abundant marginal vegetation — Watercress and Lugwigia being especially prominent.
Corydoras micracanthus has been found at elevations up to 1463 meters, possibly the highest known elevation of any Corydoradinae species. The natural temperature range is wide, shifting over the course of a year with extremes going from as low as 10°C to as high as 30°C, and possibly even higher.
At peak, the air temperature in the region can reach 40°C. Only Corydoras paleatus, Corydoras undulatus, and Corydoras longipinnis are found to inhabit cooler waters in the lower Río Paraná basin
Like so many fish, in many of its locations the habitat of this species is under serious threat, and we could lose it altogether. It’s important that those we have in the hobby are distributed amongst dedicated hobbyists that will keep and breed it to ensure its survival.
Sourcing and raising
My original group came from fellow Corydoradinae enthusiast HansGeorg Evers from Hamburg. His group was spawning during as I was visiting and so I returned home with a dozen fertile eggs.
The eggs travelled well and once I arrived home, I quickly set them up one of my small hatching containers, using water from my Corydoras pygmaeus breeding tank — this had long been stable at 20°C and 7.1pH. The eggs were placed in the container along with a couple of Alder cones, for protection against fungal attack. An air stone was added to keep the water moving, maximising oxygen levels and helping to stop any particles from settling on them the eggs and causing potential contamination.
In a little over three days, ten fry emerged, and after a further two days all ten were free swimming. At this point they were offered their first food in the form of a small amount of Micro worm. At five weeks the fry were all growing well and were moved from the hatchery container to a small shallow 15 litre, matfiltered grow out tank.
In just over five months they were not only showing signs of maturity, but were also clearly sexable — the youngsters were around 26mm SL with two females being a little larger. The group was moved to its own 30-litre tank, which was also fitted with a full-width, mature mat filter across the back, and two air-driven uplifts to create a waterflow that was more in line with the natural habitat. The tank had a thin layer of fine sand, as well as a scattering of some larger 30-40mm pebbles, and a few pieces of bog wood with Java ferns or Anubias growing on them.
There was also a large clump of Java moss, and the surface was almost completely covered with Indian fern. One floating and one sunken polyester spawning mop were also added.
Ten or twelve weeks later, I spotted what I thought were a couple of tiny fry scurrying around under a small piece of bogwood. After moving some of the tank decoration I discovered nine in total, that looked to be from at least three different spawns — the smallest appeared to only be a few days old at a little over 7mm long total length.
The largest, judging by their size of 12mm SL, and with colours resembling those of the adults looked to be at least four weeks old, which by then were then approaching just nine months of age, making them less than a year old when they first spawned.
Settling the new arrivals
I set up another small 15-litre growing on tank, fitted out with a mature mat filter, a thin layer of fine sand, a few beach twigs, some flat pebbles and a clump of Java moss. The tank was filled with 50/50 mix of water from the parents’ tank and HMA filtered water, and this was given a couple of days to settle before the nine fry were transferred. The original adult group became secretive for a while, but after a couple of weeks they were observed more frequently, especially after the tank lights went off and only the fish house main light was on, leaving them in semi darkness for 30 minutes or so before complete lights out. It was during this 30-minute evening window that the group was often seen going through courtship activity, with two or three males pursuing one of the females. Spawning activity was not observed at this time, but a few weeks later as they became increasingly settled, brief mating clinches were observed. Most of the mating activity seemed to take place in or around the base of the floating spawning mop or deep in the fronds of the large sunken mop. The eggs, fairly large at 1.7mm diameter, were almost always deposited in the sunken mop, though one or two were seen in the floating mop or the fronds of the Java moss. I found that after laying them, the adults did not really bother with the eggs, or with the emerging fry, so I tended to leave them alone and let nature take its course. However, on two occasions and just for my records, after I had determined the spawning activity was over, I did harvest the eggs and counted 12 and 10 respectively. Future spawning activity was recorded, (water parameters and conditions), but the eggs and fry were left to their own devices.
Every three or four months, or when I could see that there were lots of young in the tank, I would remove the furnishings and collect all the youngsters except for the very tiny ones — these were left with the adults. The collected fry were acclimated to the growing on tank and then released. The adults took a few days to settle back down but seemed none the worse for it.
The feeding regime was a little different for the breeding tank. Most of the time there were quite a few varying sized fry in the breeding tank, so I tended to offer crushed Fish Science Corydoras tablets, small size Vitalis Catfish granules and quite a lot of Micro worm, Grindal worm, newly hatched Artemia and finely chopped earthworm.
30% to 40% water changes were made at least three times a week. As stated earlier, in its natural sub-tropical habitat this species is happiest in water that is cooler than would usually be considered normal for a tropical aquarium. I have found the ideal aquarium temperature for breeding this species is around 18°C to 20°C. However, the species can tolerate 26°C to 28°C for short periods of time.
Unlike most Corydoradinae it prefers a pH value slightly above neutral (7.0), with a pH of 7.4 being ideal. If the water is allowed to go below 7.0pH the fish will show signs of distress, will close their fins and will become lethargic and even stop feeding. My mains water is not the best quality, so either HMA or RO water is used, filtered and as necessary it is buffered to maintain the required parameters.