Taxonomy & naming
Corydoras serratus was described in 1995 by David Sands, in a set of new corys from the upper Rio Negro tributaries of Amazonas, Brazil. The Latin epithet serratus, 'saw-toothed' or 'serrated,' refers to a serrated structural feature of the fish. For decades it sat, like almost every cory, within Lacépède's enormous genus Corydoras (family Callichthyidae).
That genus had become unwieldy — well over 170 species — and molecular work showed it was not a single natural group. In 2024 Dias, Tencatt and colleagues published a large phylogenomic revision (Zoological Journal of the Linnean Society) that split Corydoradinae into several genera, among them Brochis, Hoplisoma, Gastrodermus and Osteogaster. Crucially, not every species was reassigned: Corydoras serratus falls within Lineage 1, the clade that retains the genus name Corydoras Lacépède, 1803 in the strict sense (the lineage of the type species, C. geoffroy). So unlike many of its relatives, the sawtooth cory keeps the name Corydoras serratus under the revised classification — a useful reminder that the revision did not simply rename everything, and that each species' lineage must be checked individually rather than guessed from appearance.
Morphology
This is a small, relatively slender, long-snouted cory reaching roughly 2–2.5 in depending on source and sex, with females growing larger and rounder than males. It has the standard Corydoras armour — a hard, helmet-like head, a downturned mouth fringed with three pairs of sensory barbels, and two overlapping rows of bony scutes down each flank in place of scales — but a more drawn-out, pointed snout than the round-faced 'short-snouted' corys, the longer rostrum being typical of its lineage.
The ground colour is a pale silvery-tan overlaid with fine dark spotting and a dark saddle or blotch markings on the back and through the upper body, with a dark band associated with the eye. As in all corys the first ray of the dorsal, pectoral and adipose fins is a stiff spine — a mildly venomous defence that can jab a careless hand and snag in a net.
Habitat
Corydoras serratus comes from the upper Rio Negro system of Amazonas, Brazil — the type material was collected from a tributary of the upper Negro — within the broader upper Amazon region; in the hobby it is associated with the upper Amazon and Negro drainages spanning into adjacent Peru. The Rio Negro is the archetypal Amazonian black-water river: stained tea-brown by dissolved tannins from flooded forest, very soft, acidic and nutrient-poor.
It is a fish of the shallow, sandy margins — slow stream and river edges over fine sand, with submerged wood and a litter of fallen leaves. Black-water habitats of this kind are warm, soft and markedly acidic. Like other corys it is a facultative air-breather, darting to the surface to gulp air and absorb oxygen across a vascularised hindgut, an adaptation suited to the warm, oxygen-poor shallows it inhabits.
Feeding
The sawtooth cory is a benthic omnivore and detritivore. In the wild it works the sandy bottom continuously, burying its long snout and barbels to taste out small invertebrates, insect larvae, worms, micro-crustaceans and detritus, expelling cleaned sand through the gill openings as it goes. The longer rostrum of the long-snouted corys is well suited to probing deeper into soft substrate. In the aquarium it takes good-quality sinking dried foods alongside small live and frozen items — bloodworm, brine shrimp, chopped earthworm — and should have a varied diet rather than being left to scavenge leftovers.
Mating
Corydoras are egg-laying shoalers with no pair bond and a distinctive, well-studied courtship that the sawtooth cory is expected to share. When a female is ready she cleans a site and the group becomes active; a male positions himself at right angles to her head in the classic 'T-position,' and she appears to take his milt directly. The sperm is thought to pass rapidly through her gut to fertilise the small number of eggs she clasps in a basket formed by her pelvic fins, which she carries to a cleaned surface — a leaf, a stone, the glass — and presses into place, the sequence repeating a few eggs at a time.
Breeding
Little is published on the deliberate captive breeding of Corydoras serratus specifically; it is an uncommon, collector-grade black-water species rather than a commercially farmed cory. It is expected to breed along standard Corydoras lines: a group skewed to more males than females, spawning triggered by a large, cooler, soft water change that mimics the onset of the rains, with adhesive eggs scattered onto plants, wood and glass. The eggs receive no parental care — adults will eat them, so breeders remove either the eggs or the parents — and typically hatch in three to four days, the fry taking microworm and baby brine shrimp once the yolk sac is absorbed.
In the aquarium
The sawtooth cory is a soft-water specialist better suited to keepers who can reproduce its acidic, black-water origins than to absolute beginners. It is a shoaling fish and is genuinely stressed when kept alone or in pairs — keep six or more, and they reward you with constant, confident foraging.
Substrate matters: provide soft sand or very smooth, fine rounded gravel, because corys feed by sifting and sharp or coarse gravel erodes and infects their barbels, leaving the stubby, blunted faces that signal poor husbandry — a particular risk for a long-snouted species that probes deeply. Coming from soft, acidic Negro water, it does best in soft, warm (about 73–81 °F), slightly to moderately acidic water, well-filtered and well-oxygenated with gentle flow and regular changes; tannin-stained 'blackwater' set-ups with leaf litter and wood suit it well. It is utterly peaceful and suits a community of small tetras, pencilfish, rasboras, dwarf cichlids and other calm fish — never anything large enough to bully it. Two standard cautions: the fin spines can catch in nets (a cup is safer), and a distressed cory can release a skin toxin that, in the confined volume of a bag, can kill the whole group, so transport with care.
Conservation
Corydoras serratus has not been assessed by the IUCN Red List, so it carries no formal conservation status. It is a localised black-water species of the upper Rio Negro region, and as with other narrow-range Amazonian endemics that limited distribution is worth noting: the broad pressures on Amazonian freshwaters — deforestation, agricultural and mining run-off, damming and changes to water chemistry — could degrade the soft, acidic, sandy shallows it depends on. There is no evidence the aquarium trade threatens it, but a soft-water specialist with a restricted range is exactly the kind of fish whose status would be worth assessing on its own terms.