Taxonomy & naming
Salminus affinis was described by the Austrian ichthyologist Franz Steindachner in 1880. It belongs to the genus Salminus, a small group of large-bodied, fast-swimming predatory characins historically placed in Characidae and today generally referred to the family Bryconidae, sister lineages to the tetras and closer in build and habit to the Paraná golden dorado, Salminus brasiliensis, than to any of the small aquarium characins that share the order Characiformes. The genus name itself nods to that resemblance to the Old World salmon (Salmo), a comparison early European naturalists reached for repeatedly when they encountered these deep-bodied, golden, strongly migratory South American predators.
The species epithet affinis is Latin for "related" or "neighbouring," reflecting its close resemblance to other Salminus species described earlier, most obviously S. brasiliensis. Salminus affinis is the only member of the genus native to Colombia's Caribbean-draining river systems; the Catalog of Fishes (Eschmeyer, California Academy of Sciences) treats it as a distinct, valid species restricted to that country, and it should not be confused with the golden dorado of the Paraná-La Plata system further south, which is a separate species with an overlapping common name.
Morphology
Salminus affinis has the classic dorado build: a robust, laterally compressed but deep-bodied and muscular frame, a large terminal mouth armed with strong conical teeth suited to seizing and holding prey fish, and a deeply forked tail built for bursts of speed. FishBase records a maximum published length of 18.5 in standard length for typical adults, with an exceptional record of 31.5 in total length and 2.3 kg documented from the Rio Nare in the Magdalena basin — figures that place this species firmly among the larger predatory characins rather than anything resembling a typical community aquarium fish.
Colouration follows the dorado pattern shared across the genus: bright silver-to-golden flanks that give the group its Spanish common name, with darker fins, a streamlined, powerful profile and the deep body typical of an ambush-and-pursuit predator adapted to fast-flowing river channels rather than still water.
Habitat
Salminus affinis is endemic to Colombia, restricted to the Magdalena-Cauca, Sinú and Rancheria river drainage systems — all Caribbean-draining basins on the country's Andean and coastal lowlands. FishBase describes it as benthic-pelagic, meaning it ranges through the water column from open mid-water to near the bottom, consistent with an active predator patrolling river channels rather than a fish tied to a single microhabitat.
As a large-river predator in Andean-fed drainages, S. affinis experiences the strong seasonal flow and flood-pulse dynamics typical of the Magdalena basin, and its movements are closely tied to that hydrology — the cache notes breeding activity peaking in the rainy season, which is characteristic of migratory characins timing their reproduction to rising water levels. Specific temperature and pH data for this species were not found in the available sources; broadly, Magdalena-basin lowland rivers run warm and are not blackwater-extreme, but precise figures should be treated as data sparse rather than assumed.
Feeding
Salminus affinis is piscivorous, a predator that takes other fish and insects as its primary diet — consistent with its large mouth, strong dentition and powerful, fast-swimming build. This puts it at the predatory end of the characin spectrum shared with its genus relative, the Paraná golden dorado, rather than with the omnivorous, detritus-grazing habits typical of many of its smaller relatives among the hemiodontids and curimatids.
In the wild it is an important target of both commercial and recreational fisheries across its Colombian range, which speaks to both its predatory habits and its size — a fish substantial enough to be worth targeting by anglers is a fish that needs a diet of real prey to reach that size, not incidental foraging.
Mating
Little detailed reproductive biology has been documented for Salminus affinis specifically, but hobby and angling accounts describe breeding activity concentrated in the rainy season, with peak gonadal development reported around November. That timing is consistent with the broader pattern among large Neotropical river characins, where reproduction is cued to rising water and the onset of the flood pulse rather than occurring year-round.
No reliable external sexual dimorphism has been documented for this species in the available sources; this should be treated as data sparse rather than confirmed absence.
Breeding
Salminus affinis should be understood as a migratory food fish, not an aquarium-breedable species. Like its genus relative the golden dorado and the large Prochilodus and Semaprochilodus migrators it shares its rivers with, it is a long-distance spawning migrator whose reproduction is tied to seasonal flooding in large Andean-fed river systems — behaviour that cannot be replicated in a home aquarium. Available accounts describe breeding activity concentrated in the rainy season with gonadal development peaking around November, but do not document a home-aquarium spawning.
Captive breeding of S. affinis is not well documented, and it is almost unknown in the aquarium hobby. Where large-bodied dorado species are propagated at all, it is typically through hormone-induced spawning at hatchery or conservation-stocking scale rather than natural pairing in captivity — this is a fish to admire and, where legal, angle for in its native rivers, not one to plan a breeding project around at home.
In the aquarium
Salminus affinis is almost unknown in the aquarium trade, and the scattered hobby accounts that exist are unambiguous about why: this is a large, fast, predatory river fish, not a tank fish. One aquarium care discussion cites a size of roughly 18 inches (17.5 in) and a tank footprint of 8 x 3 feet as the realistic minimum for a specimen approaching adult size — well beyond what all but the most dedicated large-fish keepers can provide, and consistent with FishBase's maximum length figures for the species.
Any keeper considering S. affinis needs to plan for a genuinely enormous, heavily filtered system, a piscivorous diet of appropriately sized whole prey items and fish, and a solitary or very carefully chosen tankmate list given its predatory build and jaw. Given how poorly documented captive husbandry is for this species, and its Vulnerable conservation status in the wild, there is little practical case for keeping it outside large public-aquarium or specialist large-fish setups — this is fundamentally a river gamefish, not a community or even a typical large-tank species.
Conservation
Salminus affinis is assessed as Vulnerable by the IUCN Red List. Populations are decreasing across its restricted Colombian range as a result of hydroelectric dam construction, overfishing and water pollution — pressures documented in the academic literature on threatened fishes of the Magdalena-Cauca system, one of Colombia's most heavily dammed and industrialised river basins. The species is targeted by both commercial and recreational fisheries throughout its range, adding direct harvest pressure on top of habitat degradation.
Because S. affinis is endemic to a small number of Colombian drainages rather than distributed across a continental river system, it has far less range to absorb these pressures than a widespread Amazonian species would. Its status is a clear example of a large-river migratory predator whose survival is tied directly to free-flowing river connectivity — exactly the kind of habitat that hydroelectric development fragments — and it stands as a conservation-priority species within Colombia rather than a hobby or trade species of any consequence.