Order Siluriformes
Family Callichthyidae (Armored Catfishes)
Subfamily Corydoradinae
Genus Corydoras
The genus Corydoras includes many species of small catfishes native to the rivers of South America. A characteristic feature of these fish is a short, high body with flanks densely covered by two oblique rows of bony scutes, creating the impression that the fish are dressed in a hard armor shell, providing reliable protection against predators. Hence, they are commonly called armored catfishes. Sometimes, if a catfish swims into a narrow crevice, it may become trapped and die, so it is very important to consider this feature when setting up the aquarium.
They are small in size, ranging from 2.5 to 12 cm. Corydoras possess an adipose fin, and the larger dorsal and pectoral fins are equipped with stiff spines. There are two pairs of barbels on both the upper and lower jaws. A unique feature of these catfishes is their ability to breathe atmospheric air by swallowing it at the water surface, which they reach by swimming upwards. Therefore, the aquarium must provide free access to the water surface so the fish can gulp air.
Sexing Corydoras is quite easy. Adult females look more rounded compared to males, a difference easily noticeable when viewed from above. In females, the pelvic fins resemble a fan, while in males, they look like a spear. The upper margin of the dorsal fin is pointed in males and rounded in females. When purchasing, carefully inspect the fish for any unusual growths or spots. These could be fungus, external parasites, or other diseases.
Also, pay attention to reddish spots on the body of the Corydoras, especially on the belly. Most of the time, this is a sign of a bacterial infection, and there is almost no chance of saving the fish. It is very important that their barbels are intact. Damaged barbels can indicate a weakened fish or illness. Sometimes, Corydoras with damaged barbels stop eating and die. A good indicator of the health of these fish is the body sheen, which is clearly pronounced in healthy specimens.
Keeping Corydoras is simple. Most species are bottom-dwellers and love to dig and stir up the substrate, so try to avoid very fine sand; rounded gravel of 2-3 mm is best. Unrounded sand and sharp-edged gravel should not be used as substrate, as the fish can injure their mouths and barbels on them.
Corydoras are schooling fish and feel much better and more confident in a group of 4-5 individuals. Often, even Corydoras of different species will school together. These fish love to hide, so providing various hiding spots is necessary for their well-being. Place several small driftwood pieces mimicking branching roots or cave-like shelters (flower pots, tubes, flat stones stacked in a checkerboard pattern; bamboo also looks great in the aquarium). They love shelters and readily rest on stones.
Filtration and regular partial water changes are mandatory. They prefer slightly acidic and soft water, but adapt well to hard and slightly alkaline water. They accept all kinds of foods, including live, frozen, and dry foods. The main condition is that the food must reach the bottom, as they feed exclusively from the substrate. Corydoras poorly tolerate heavy metal salts in the water, especially copper, as well as common table salt. It is important to remember this when medicating the fish. They thrive in water hardness up to 20°dGH, pH 6.0–7.5, and temperatures ranging from 17 to 32°C.
As the largest genus, Corydoras includes over 100 species, all with similar body shapes. Some species do not grow large and are referred to as “dwarf” armored catfishes. These include C. habrosus, C. hastatus, and C. pygmaeus (around 3 cm). The most well-known standard-sized species (5-7 cm) include C. aeneus, C. agassizii, C. atbiacus, C. arcuatus, C. elegans, C. melanistius, C. metae, C. nattereri, C. paleatus, C. punctatus, C. rabauti, C. reticulatus, C. schwartzi, C. trilineatus, and C. undulatus. Even more desirable for aquarists (though harder to find) are C. bondi, C. delphax, C. guapore, C. haraldschultzi, C. leucomelas, C. melini, and C. ornatus.
According to Sterba, Corydoras can be conditionally divided into 4 groups for purely practical purposes:
1. — C. aeneus, C. elegans, C. eques, C. macropterus, C. nattereri, C. paleatus, etc. Modest coloration, mostly greenish (with a metallic sheen) with indistinct spots or patterns, and plain greyish fins. Maintenance water temperature 20–24°C (extreme limits 15–18 and 30°C). Breeding is uncomplicated.
2. — C. agassizii, C. caquetae, C. caudimaculatus, C. haraldschultzi, C. julii, C. melanistius, C. punctatus, C. reticulatus, C. sterbai, C. trilineatus, etc. They feature distinct dark spots, stripes, or both on a silvery background. Fins are usually colorless and transparent, with a large dark spot on the dorsal fin; the adipose, anal, and especially caudal fins are covered with several dark vertical rows of spots. Water temperature 25–28°C. Breeding is moderately successful with low productivity.
3. — C. arcuatus, C. axelrodi, C. boesemani, C. metae, C. panda, C. rabauti, C. schwartzi, etc. They have one or more longitudinal stripes along the upper body on silvery-white, yellowish, or orange flanks, while fins are mostly plain and unpatterned.
4. — C. cochui, C. hastatus, C. habrosus, C. pygmaeus, C. gracilis. Small-sized species.
There is also an informal classification based on groupings of similar coloration or body shape:
— Vertically oriented black stripe passing through the eye, speckled body pattern (C. atropersonatus; C. agassizii; C. melanistius; C. schwartzi).
— Speckled body without a black stripe through the eye (C. julii; C. leopardus; C. sterbai; C. maculifer). Single black stripes (spots) of varying width and length on the body (C. arcuatus; C. adolfoi; C. narcissus; C. metae; C. panda).
— Relatively large, irregularly shaped dark spots scattered randomly on the body (C. sarareensis; C. elisae; C. paleatus).
— Black horizontal stripe down the middle of the body from the gill cover to the end of the caudal peduncle (C. bondi; C. nattereri).
— Black vertical stripe through the eye, two horizontal black stripes on the body (C. axelrodi; C. loxozonus).
— Primary body color black (C. barbatus; C. lacerdai).
— Several alternating horizontal light and dark bands (dashed lines) on the body (C. elegans; C. latus; C. napoensis; C. undulatus).
— Metallic sheen across the entire body (C. aeneus; C. bolivianus; C. concolor).
— Dark back (C. zygatus; C. rabauti; C. goessei).
— Large dark spot on the caudal peduncle (C. caudimaculatus; C. guapore; C. hastatus).
It is important for aquarists to know maintenance and breeding conditions. Neither classification based solely on external features helps much in this regard, as species with very different care requirements and breeding difficulties end up in the same group. A more useful division for aquarists is grouping Corydoras into short-snouted and long-snouted types. As a rule, long-snouted Corydoras are much more challenging to keep and breed.
Other species kept in aquariums include: — Corydoras acutus [Cope, 1872] – Blacktop Cory. Peru, Ecuador. 6 cm. Body color is olive-brown with a white belly, a faint pale lateral stripe, and a large black spot on the upper dorsal fin (geographic variants without this spot exist). Sides of the head and gill covers have a blue sheen. Forked caudal fin with four vertical stripes; — Corydoras albolineatus [Knaack, 2004] – (C 056). Bolivia. 4 cm. Body features a wide white longitudinal stripe and numerous small brown spots on the top of the head and snout; all fins are unspotted; — Corydoras ambiacus [Cope, 1872] – Spotted Corydoras. Peru. 6 cm. Elongated snout. Straw-colored body with numerous irregular dark brown spots on the flanks. Cheeks with a blue sheen. Dorsal fin has a large black spot on the anterior half, extending onto the back around the fin base. Spots are also present on the anal fin. Four vertical brown spot-stripes on the caudal fin. More active at night and should be fed late in the evening; — Corydoras davidsandsi [Black, 1987] – Sand Cory. Rio Negro basin. 7 cm. Peaceful, schooling fish. Lifespan up to 6 years.
Identification: Genus Corydoras — Corydoras ambiacus, davidsandsi.
— Corydoras pastazensis [Weitzman, 1963]. Pastaza Cory. Ecuador. 6 cm. Snout slightly more elongated than in relatives, with 2 pairs of barbels on the upper lip. Light grey body background with a slight amber tint. Temperature increases make the color yellowish-brown, while decreases shift it to lighter, violet-toned hues. Small black spots—more prominent depending on sexual activity and diet—cover the flanks, back, head, and entire caudal fin. Two vertical black stripes: the first passes through the eye down to the throat, the second from the first dorsal fin rays down to the belly. Pectoral, pelvic, anal, and adipose fins are nearly transparent. First rays of the dorsal fin are black. Females have rounded pelvic fins, unlike males which have slightly narrower ones. Diet mainly protein-based, live and frozen foods; — Corydoras semiaquilus [Weitzman, 1964] – Peru Black Cory. Peru, Brazil, western Amazon basin. 6 cm. Dark grey to brown body with black scales on the upper part and a lighter belly. Highly variable species. Fish from different small tributaries of the same river often have different colorations. Specimens from Peru are darker than those from Brazil. Similar to C. fowleri. These fish can be quite aggressive; provide plenty of hiding spots. Most active at night. Lifespan up to 4 years.
Corydoras adolfoi, aeneus, agassizii, arcuatus.
Scleromystax barbatus, macropterus, prionotos. 
