The genus Scleromystax is a relatively small group , consisting of approximately seven recognized species and six distinct varieties that are not yet formally described. The genus was split from Corydoras in the early 2000s and members are relatively large (compared to cory catfish) and tend to be cryptically colored. They are found primarily in Brazil, along the eastern seaboard of the country.
Scleromystax barbatus has a limited natural distribution around Rio De Janiero, Brazil. While the species has a limited natural distribution, it is likely the most widely distributed species from the genus in the hobby (at least in the US). It is large (by Corydoradinae standards) reaching approximately four inches in length, but it grows and matures slowly.
I purchased a group of six small (approximately one inch) fish from a club auction in 2013. By early 2014 the fish were around 2.5 inches and the females had started laying clusters of eggs, none of which were fertilized. This continued through 2014 and into late 2015, at which time the eggs finally began to be fertilized. I was still several months before I would have more than one or two eggs per clutch hatch, and in mid-2016 I was finally able to produce enough fry (8) for me to consider the breeding a success. My research indicates that this is not the experience of everyone, but most agree that the species matures slowly and is difficult to breed successfully.
I housed my adults together in a 40 gallon (long) aquarium, with a sand substrate. Filtration was provided by a hang-on filter and a large sponge filter, and additional circulation was provided by a powerhead on one end of the tank that directed flow to the other end. The tank was near the floor of my basement and was kept unheated (typical temperatures were around 70 degrees F). I added a heater on two separate occasions and the animals became visibly stressed when temperatures reached around 76 degrees F so the heaters were removed. Water in the tank was Louisville tap water (HARD). Water changes were 40-50% once per week.
The adults greedily accepted virtually any food offered. The maintenance diet was primarily one daily feeding of frozen food (spirulina enhanced brine shrimp, bloodworms, beefheart, or mysis shrimp) and one daily feeding of prepared food (flake, pellet, wafer, or gel). Occasional feedings of live white worms or live black worms were devoured.
Eggs were laid regularly in the main tank but were typically eaten within 3 days. Eggs pulled from the main tank rarely hatched. When eggs started occasionally hatching from the main tank I moved one mature male and two mature females to a 20 gallon long tank. This tank had water matching the main tank at first but was transitioned over a period of two weeks to very soft, acidic water. After the adjustment period the breeding tank was approximately 90% RO water with the PH adjusted to 5.8-6.0. The bottom of the breeding tank had no substrate but was heavily littered with leaves (oak and Indian Almond). It was filtered by a large internal box filter with very high airflow and there was an airstone placed on the opposite side of the tank for additional circulation.
The fish spawned in a typical corydoras fashion. The females laid a few eggs at a time in their pectoral fins while taking on a typical ‘T Position’ with the male to fertilize them. The eggs were then placed on a solid surface (almost always on the aquarium glass). Unlike corydoras however, the eggs were rarely scattered around the tank. Instead they were normally placed in one or two large clusters. At 70 degrees F the eggs hatched in around six days, with the fry becoming free swimming around 24 hours later.
With Scleromystax barbatus, unlike many other species, the difficulty in raising them was in getting fry, not in raising them. Free-swimming fry were able to take baby brine shrimp from the start. In addition to the baby brine shrimp they were also given microworms, receiving a feeding of one of these approximately four times each day. After two weeks the diet was supplemented with ground flakes and ground pellets. After one month small grindal worms were introduced. Small (10%) waterchanges were conducted daily for the first several weeks and the fry grew quickly. Within two weeks they were showing coloration similar to the adult females and within one month they were very similar in appearance. By the time they were two months old they were approximately one inch.
Scleromystax barbatus was a very frustrating species for me to breed. The adults were relatively hardy and produced eggs regularly, but it took many, many tries before I would be able to get a single viable fry, and many more before I would consider the breeding a success. The adults are interesting in appearance and tend to not bother any other fish kept with them. They would go good in many cool water tanks, but breeding them was an enormous challenge for me.