The evolution of dwarf fish forms has taken place independently in many different regions of the world. Among the armored catfishes (Corydoradinae), there is a small group of species that are believed to have evolved millions of years ago. These dwarf Corydoras live in the great clearwater rivers of the 500-million-year-old Brazilian Shield.
The South American continent is comprised of very different geographical regions. Large mountain ranges created by tectonic plate shifts, such as the still-young Andes or the 1.9-billion-year-old formations of the Guiana Shield, frame the three major river basins of South America. Between the Guiana Shield and the ancient Brazilian Shield lies the largest and most famous: the Amazon Basin. Further east, between the Atlantic Shield and the Brazilian Shield, are the Maranhao Basin to the north and the huge Parana Basin to the southeast.
The major rivers that flow down from the mountain ranges (serras) of the Brazilian Shield and drain northward into the Amazon Basin have still not been fully explored ichthyologically, particularly the headwaters. The ancient, eroded rocks through which the spring waters flow effectively filter out any sediments, ensuring that the water in the tributaries—and, outside the rainy season (January to April), in the great rivers—is very clear.
The major river basins of the Rio Tapajos in the west, the central Rio Xingu, and the Rio Araguaia and Rio Tocantins further east are separated by the Serra do Cachimbo, the Serra do Roncador, and other, smaller mountain ranges. Driving along the few roads in the mountain ranges that act as watersheds and separate the river systems, you can clearly see what river system the water belongs to based on the collected fish species.Many endemic species
I drove through the area of the Serra do Roncador twice and could clearly see that very different species of fish occur in the headwaters of the Rio Xingu (catchment of the Rio Sete do Setembro, Suia Missu, and other rivers) than further east, beyond the serra, in the drainage of the middle Rio Araguaia basin.
Separated over millions of years, many endemic species have evolved in the three major clearwater rivers of the Brazilian Shield. Some are limited in their distribution to only a few square kilometers.
The loricariids that have colonized the numerous rapids and waterfalls of the Rio Xingu are a prime example. The armored catfishes (Corydoradinae) of these three river basins are distinct as well.
So far, most aquaristically known species from these rivers have not been scientifically studied and are still awaiting description. Hence, we use a code system for the armored catfishes exactly like the L-number system used for the loricariids. Most Corydoradinae from the Rio Araguaia, Rio Xingu, and Rio Tapajos are therefore only known by a C-number (C stands for Corydoradinae).
In discussing my experiences with these three species, I will start from the east and go west, because the only scientifically described species lives in the drainage of the Rio Araguaia and has been the subject of taxonomic discussions among aquarists in the past.
Corydoras cochui, Barredtail Cory
In 1954, Myers and Weitzman described a small catfish as Corydoras cochui in honor of its discoverer. Fred Cochui, the owner of the New York importer Paramount Aquarium, had caught the species on one of his trips to Central Brazil, in the Rio Araguaia near Santa Maria Nova. Cochui, who was very active, and his friend Stegemann established the collection of tropical fishes in the small town of Aru-ana, on the middle Rio Araguaia in the state of Goias.
After he received additional specimens from Fred Cochui, Weitzman added to the sparse data on C. cochui in a subsequent paper (1956). He clearly stated that C.cochui is a dwarf species. However, in the trade of the 1970s and 1980s, Corydoras habrosus, regularly imported from Colombia, was incorrectly referred to as C. cochui (e.g. Franke, 1985). This was later corrected, thanks to the knowledge about the country of origin and evidence of the genuine C. cochui occurring in the drainage of the Rio Araguaia.
The collectors that caught fishes for Paramount Aquarium, and later for other companies, all lived in the small town of Aruana. In the 1950s and 1960s, many fish species were collected in the area and served as material for scientific descriptions. One of the collectors, Savio Valerio da Silva, later worked for the company Trop Rio, based in Rio de Janeiro. I have a longstanding friendship with the manager, Marco Tulio Lacerda, and thanks to his connections, I have been able to make numerous collecting expeditions to Brazil.
Together with Savio’s son Paulo, who later took over his father’s business, I made many collecting trips in the 1990s. Paulo showed me all the places along the Rio Araguaia where his father had collected armored catfishes. In the nearby Rio do Peixe, and, during high-water season, in the mighty Rio Araguaia, C. cochui lives in huge schools of several thousand fish.
In the low-water season, from May to September, C. cochui lives in smaller groups in the small streams called igarapes, along the sandy banks and among fallen leaves in the shaded gallery forest of the shore region. There, the groups spawn with the onset of heavier rainfalls and the young fish dine at a richly laid table in the now-flooded shore region at the beginning of the high-water period.Later, the adolescents migrate in huge schools into the Rio Araguaia, and they can be collected there by the thousands with a net.
On March 20, 1998, during the high-water season in the Rio do Peixe, I measured a water temperature of 87°F (30.7°C), 42 S/cm, and a pH of 6.7 on the banks of a sandbar. There, we caught hundreds of C. cochui with a single draw of the 50-foot (15m) seine.
I was breeding C. cochui by the mid-1990s. The fish came to me from the Rio do Peixe via Trop Rio and Aquarium Dietzenbach. The species is easy to reproduce and raise. A few weeks of conditioning with good food and regular water changes after a six-week break quickly trigger the whole group to spawn. Like C. sp. C22 from the Rio Xingu,
C. cochui always deposit a single, relatively large egg per mating.
The eggs of all three species presented here are significantly larger than the eggs of C. hastatus or C. pygmaeus. Unfortunately, I was unable to document the development of the juveniles in photographs. I regret this, because photos would be very helpful in determining to what extent the development of C. cochui differs from that of the very similar C. sp. C22 discussed next. Unfortunately, tropical fish collecting in the state of Goias has been outlawed for several years, so it looks as if the true C. cochui may never return to our aquariums.
Corydoras sp. C22
Almost 20 years ago, I introduced a new dwarf catfish under the code number C22 (Evers, 1994). I received the fish from Transfish in Altamira, which was still active at that time. Later I considered the species as belonging to C. cochui (Fuller & Evers, 2005). Today, however, after studying the facts and comparing the two species, I am of the opinion that C. sp. C22 is an undescribed dwarf armored catfish from the Rio Xingu.
In 2006, I was able to collect the species in the area of Altamira. Since then, I have maintained and reproduced it in the aquarium. In 1994, I had only a few specimens of C22, which I failed to breed. However, I can confirm now that the two species differ in coloration.
The true C. cochui, particularly the males, clearly show four elongated rectangular blotches along the side of the body. This pattern is not present in C. sp. C22. These fish have only a few irregular blotches and spots along the side of the body. In addition, C. sp. C22 appears more elongated in the rear third of the body than C. cochui. Fortunately, C. sp. C22 is exported every now and then from Brazil. We should keep these fish under the code designation C. sp. C22.
In July 2006, I visited the small town of Altamira on the lower Rio Xingu with my friend Marcos Wanderley from D’Agua (Recife). This time, in addition to the almost obligatory loricariids, I wanted to study the armored catfishes of the area. Together with Marcos’s supplier,
Tim Ne of Aquario Xingu, we went to the Rio Ituna and Rio Itata, two direct tributaries of the Rio Xingu. Across from Altamira, they can be reached via an unpaved laterite road.
We easily caught a few dozen C22 over fine sand in the Rio Itata. During low water, the very slow-flowing, clear river had a pH of 5.8, 32 ^S/cm, and a temperature of 86°F (30°C) near the shore. Large schools of the species were observed moving along the shoreline over the fine sand and nosing through it for food. Just as they do in the aquarium, the small catfish stuck their heads into the fine sand down to their big eyes. Like their counterparts from the Rio Araguaia, this species lives on the sandy banks and can even be observed in the daytime.
Corydoras sp. C22 is relatively easy to spawn. For the other two species, the most important water parameter is a higher minimum temperature of 79°F (26°C). Especially the juveniles of these dwarfs are very sensitive, and at low temperatures the animals develop poorly. Juveniles sexually mature within four to five months at 82°F (28°C). Only the next species, C. sp. C144, requires considerably longer; it is also the most difficult of the three from the Brazilian Shield to keep and breed. However, in my opinion it is also the most interesting.
Corydoras sp. C144
In 2005, I published an article presenting the armored catfishes of the lower Rio Tapajos and assigned a few new C-numbers. Among them was a new dwarf catfish that I collected in the Igarape Pimental and in the Rio Tapajos near the small town of Pimental. Again, this dwarf cory lived in large groups over sandy shore areas and was easy to catch during the day. The night before, we had desperately struggled in the igarape to capture even a single animal. In the Rio Tapajos and the Igarape Pimental, the water was very soft and slightly acidic (pH 5.0—5.5 and conductivity of 20 ^S/cm or less). In the main river, the temperature was 84-87°F (29.0-30.5°), and in the igarape it was slightly lower at 82°F (27.5°C).
Corydoras sp. C144 has the most elongated shape of the three species. The distance between the dorsal and adipose fins is remarkably long. Even at the young age of about two weeks, the long body is noticeable.
The species has its own unusual form of locomotion. Especially during courtship, the males literally hop around the females. Even outside the reproductive phase, the animals often sit slightly propped up on their pectoral fins, aligned in one direction. They escape with little hops if you get too close. In that regard, they resemble the darter tetras (Characidiinae).
Unfortunately, C144 has not been commercially imported so far. I could barely maintain the few specimens that I brought back from my trip in 2003. No catfish friends to whom I had given juveniles were able to breed them. The animals are very delicate during breeding, and even in pure reverse-osmosis water the fertilization rate is poor. Breeding is difficult and the animals are very vulnerable to the stresses of shipping.
Based on the three species from the Brazilian Shield presented here, I hope that I have shown how interesting it can be to work closely with armored catfishes. These three species inhabit exactly the same type of habitat in the three mighty clearwater rivers of the Brazilian Shield. It would certainly be worthwhile to examine this subject scientifically in more detail. Do the three have the same ancestor, or are they the result of convergent evolution?
These species are indeed more suited for the advanced aquarist, but well worth the time. I have been fortunate to observe all three species in nature and in the aquarium, and have been more or less successful in breeding them. Perhaps this article will motivate some other catfish friends and enthusiasts to try these dwarfs.