Corydoras acutus

Corydoras: from the Ancient Greek κόρυς (korus), meaning ‘helmet’, and δορά (dora), meaning ‘skin, hide of an animal’, in allusion to the rows of bony plates on the flanks of genus members.

acutus: from the Latin acutus, meaning sharpened, in allusion to the shape of the species' snout.

Type locality is 'Río Ambiyacu, Shansho Caño, Loreto, Peru', with 'Ambiyacu' an apparent misspelling of 'Ampiyacu', a small river running into the Amazon west of the town of Pebas.

It's currently understood to occur throughout parts of the upper Amazon basin in Brazil, Peru, Ecuador, and possibly Bolivia, including the rios Yavarí, Abunã (rio Madeira system), Nueva Rocafuerte (Río Napo system), and Huitoyacu (Río Marañón system).

Unsurprisingly given this relatively large range, it can vary somewhat in appearance depending on collection locality with some specimens lacking a dark marking in the dorsal-fin, for example.

Ideally use a substrate of fine sand, although rounded gravel is an acceptable alternative provided it's kept scrupulously clean.

Other décor is largely down to personal choice, but some cover should be provided to give the fish security.

Corydoras spp. are foraging omnivores and will accept most sinking dried foods, as well as small live and frozen varieties such as bloodworm, Tubifex, etc.

Feeding a varied diet will ensure the fish are in optimum condition.

Under no circumstances should they be expected to survive on 'left-overs' from other inhabitants of the aquarium or relied on to 'clean' the aquarium.

Females tend to grow larger, and sexually mature individuals are noticeably rounder and broader-bodied than males, especially when gravid.

This species can be confused with three similar-looking fishes of uncertain taxonomic status which have been assigned the C numbers C024, C077, and C109 in the aquarium hobby.

C024 and C109 are unlikely to be conspecific in that they occur in Pará state, Brazil, several thousand kilometers outside the range of C. acutus, in the rio Guamá (Tocantins drainage), and lower rio Xingu, respectively.

However in the rio Abunã, a tributary of the Madeira in Acre state, Brazil, C077 occurs sympatrically with C. acutus and a similarly-patterned, short-snouted form known to hobbyists as C076.

C. acutus apparently grows larger than C077, but additional diagnostic characters are lacking at this time.

The original description by Cope is very short and reproduced here:

'A stout species, differing from the others, especially in the attenuation of the muzzle, which viewed from above is narrow, and contracted abruptly from the general outline. Mouth inferior, lower lip wanting or not reverted. Head 3.1 times in length without caudal, 1.33 times in depth. Orbit three times in head, 1.33 times in the nearly flat interorbital space. Lateral scuta 22-21; no azygus plates. Radii D. I. 7; A. I. 6; V. 6; P. I. 5, the spines serrate on the inner side. Dorsal spine serrate posteriorly on the distal half. Adipose spine without fin, stouter than anal spine. Caudal fin furcate.

Color olive (faded), a faint pale band on each side; a large black spot on distal part of dorsal rays. Caudal with four vertical bars; clavicle and operculum with blue reflections. Length .051 m., depth .0155 m.'

The genus Corydoras held over 150 valid species until Dias et al. (2024) divided it into five genera.

It is included in the family Callichthyidae, of which members are often referred to collectively as 'armoured' or 'mailed' catfishes group due to the presence of bony plates in place of scales on the body.

Their taxonomy can be confusing, and numerous undescribed species are also thought to exist.

Fish of unconfirmed identification entering the aquarium hobby are therefore typically assigned a 'C' or 'CW' number for purposes of reference and organisation.

They are facultative air breathers and possess a modified, highly vascularised intestine which has evolved to facilitate uptake of atmospheric oxygen and aid survival in oxygen-deprived environments. In the aquarium you'll occasionally see them rising to the surface to take in gulps of air.

The stiffened pectoral-fin spines are capable of piercing human skin and a 'sting' can be very painful indeed, so care should be exercised when handling them.

It is thought that secretions from the axillary glands at the base of each spine may even be mildly toxic or venomous.