Taxonomy & naming
The coast cory was described in 1980 by Han Nijssen and Isaäc Isbrücker as Corydoras prionotos, from Lagoa Juparaná in the Rio Doce system of Espírito Santo, Brazil — the type locality. For its first decades it was treated as one of the many Corydoras, and that is the name under which it first reached aquarists.
It now sits in Scleromystax Günther, 1864, a small genus resurrected from synonymy by Marcelo Britto's 2003 phylogeny of the Corydoradinae. Scleromystax comprises a tight, monophyletic group of highly sexually dimorphic catfishes that, despite their cory-like appearance, are more closely related to Aspidoras than to Corydoras proper; Britto & Reis (2005) recognised S. barbatus, S. macropterus, S. prionotos and the then-new S. salmacis. The 2024 phylogenomic revision of the Corydoradinae by Dias, Tencatt and colleagues, which split the old grab-bag genus Corydoras into seven lineages each with its own available name, kept Scleromystax intact as a valid genus — so unlike many former corys, prionotos did not change name in that revision; it had already moved years earlier. Eschmeyer's Catalog of Fishes lists it as valid as Scleromystax prionotos (Nijssen & Isbrücker 1980). The species had in fact been seen even earlier: Weitzman (1955) discussed the same fish under the name Corydoras nattereri triseriatus.
Morphology
This is a small, fairly elongate corydoradine, reaching about 2 in in standard length. It has the family's armour of two overlapping rows of bony plates down each flank, a helmeted head and three pairs of barbels around a small, sub-terminal, down-curved mouth. The serrated medial border of the pectoral spine — the feature the species is named for — runs along that stiff leading fin ray.
Its most striking trait is its sexual dimorphism, the hallmark of the genus. Mature males develop patches of stiff bristle-like odontodes on the cheek — the preopercular and opercular region of the head, set in fleshy papillae — and grow elongated dorsal and pectoral fins. In the most extreme Scleromystax (S. barbatus) those male fins can reach back toward the tail and the cheek bristles cover a broad area; in S. prionotos the development is real but more restrained, with cheek odontodes and fin elongation less pronounced, and conspicuous only in larger males. The two sexes also differ in the shape of the genital papilla, lanceolate in males, and in body proportions. Colour is a mottled brown over a paler ground, with darker transverse blotches along the body — cryptic, stream-bottom camouflage rather than the metallic sheen of the emerald corys.
Habitat
Scleromystax prionotos is endemic to the Atlantic-slope coastal river basins of south-eastern Brazil. Britto & Reis (2005) give its range as running from around Trancoso in southern Bahia south to the Rio Ribeira de Iguape basin, taking in the Rio Doce system of the type locality; FishBase frames the same distribution more conservatively as the coastal rivers from Espírito Santo to São Paulo. Either way it is a fish of small, clear, often shaded coastal streams and their associated lagoons and slow reaches, not of the great interior river systems.
These are warm but not hot waters, and reported aquarium parameters reflect that: temperatures of roughly 72–79 °F, a broad pH band around 6.0 to 8.0 and soft to moderately hard water. The fish keeps to the bottom over sand and fine sediment, among leaf litter, roots and marginal vegetation, in the gentle current of forested coastal creeks. The genus as a whole is associated with this band of coastal-stream endemism, several of its members having narrow, partly overlapping ranges along the same stretch of the Brazilian seaboard.
Feeding
Like other corydoradines the coast cory is a benthic omnivore, foraging over the substrate with its barbels for small invertebrates, worms, insect larvae and detritus, and sifting sand to expose buried food. In the aquarium it readily takes all prepared sinking foods — tablets, granules and larger flakes that settle to the bottom — and accepts live or frozen bloodworm, whiteworm, grindal worm, Daphnia and Tubifex, which are also the foods of choice for bringing a group into spawning condition. As with all corys it should be given proper sinking food of its own rather than left to glean leftovers.
Mating
Scleromystax spawn in the egg-laying, shoaling manner shared across the Corydoradinae, with no pair bond, and the genus's pronounced dimorphism makes courtship visibly male-driven. A ripe female cleans a site, and a male adopts the classic 'T-position' at right angles to her head; she is thought to take his milt at the mouth while clasping a few eggs in a pelvic-fin basket, then carries them to the cleaned surface — plant, root or glass — and presses them home, repeating the sequence in small batches. The male's enlarged fins and bristling cheek odontodes, displayed and flared during these bouts, are the secondary sexual characters that make sexing this species straightforward in adults: the bigger-finned, cheek-bristled fish are males, the plainer, fuller-bodied ones females.
Breeding
Scleromystax prionotos has been bred in the aquarium, and breeders report a pattern typical of cooler-water corydoradines: a well-conditioned group, conditioned on live and frozen foods, is induced to spawn by a generous, cooler water change that mimics the seasonal flush of its coastal streams. The adhesive eggs are laid in small batches on firm surfaces — fine-leaved plants, spawning mops or the glass — and, as in all corys, receive no parental care, so the eggs or the parents are separated to prevent the adults eating them. The eggs hatch after a few days, and the fry are raised on microworm, baby brine shrimp and fine powdered foods once their yolk is absorbed. A cooler, well-oxygenated tank and a sex ratio skewed to extra males give the best results.
In the aquarium
The coast cory makes a peaceful, sociable and rewarding aquarium fish, and is genuinely a shoaling species — keep six or more, as it is stressed and reclusive in small numbers. Because it comes from cooler coastal streams rather than warm lowland rivers, it does best in the lower tropical range (around 72–79 °F, and it tolerates the cooler end well); pairing it with similarly cool-tolerant, calm community fish is wiser than mixing it with heat-loving tropicals.
Substrate should ideally be soft sand, with rounded fine gravel an imperfect substitute; sharp or chipped gravel erodes and infects the barbels these fish use to feed, one of the commonest signs of poor cory husbandry, so it is worth getting right. Border the tank with driftwood and plants and leave open foraging areas, with overhanging wood, rockwork or floating plants for shade to settle the fish. Good filtration with a gentle current, clean substrate and regular water changes suit it, and the genus's striking dimorphism — bristle-cheeked, long-finned males alongside plumper females — makes a settled group genuinely interesting to watch. As with all corys, handle with a container rather than a net, since the stiff fin spines snag easily.
Conservation
Scleromystax prionotos is assessed by the IUCN as Least Concern, last evaluated in 2018. It has a reasonably broad distribution across the south-eastern Brazilian coastal basins and is not at present considered threatened. That said, the Atlantic Forest seaboard it inhabits is one of the most heavily settled and altered landscapes in South America: its small coastal streams are under sustained pressure from deforestation, urban and agricultural run-off, water extraction and pollution. Because the species — like its congeners — is tied to particular coastal drainages rather than a vast continental range, the slow degradation of those streams is the relevant long-term concern, even though the species itself remains secure for now. Most fish in the hobby are wild-caught from a modest, specialist trade rather than commercially mass-bred.