Taxonomy & naming
Sarotherodon nigripinnis was described by the French zoologist Alphone Guichenot in 1861, in a paper that appeared under Auguste Duméril's editorship in the Archives du Muséum d'Histoire Naturelle. Guichenot placed it in the broad nineteenth-century genus Tilapia, as Tilapia nigripinnis, working from two syntypes collected in Gabon (now held at the Muséum national d'Histoire naturelle in Paris, register MNHN A-9396). The name moved into Sarotherodon — Rüppell's 1852 genus for the brush-toothed, mouthbrooding African tilapias — as part of the twentieth-century untangling of the old catch-all Tilapia into the modern genera Tilapia/Coptodon (substrate spawners), Oreochromis (maternal mouthbrooders) and Sarotherodon (paternal and biparental mouthbrooders). For a long stretch the fish was treated not as a full species but as a subspecies or synonym of the wide-ranging black-chinned tilapia Sarotherodon melanotheron: Trewavas and Teugels (1991) and the morphometric, allozyme and mtDNA revisions of Falk and colleagues (2000, 2003) recognised it as a valid subspecies within that complex. Eschmeyer's Catalog of Fishes and recent regional treatments (Stiassny and co-workers in the IRD/MRAC Lower Guinea fish volume, 2007; Skelton 2019) now list it as the valid species Sarotherodon nigripinnis. Two named forms are usually recognised: the nominate S. n. nigripinnis of Gabon and Equatorial Guinea, and S. n. dolloi (Boulenger, 1899) — honouring the Belgian palaeontologist Louis Dollo — which runs from the lower Kouilou in the Republic of the Congo to the Congo River estuary in the Democratic Republic of the Congo.
Morphology
This is a moderately deep-bodied, laterally compressed tilapia reaching about 7 in in standard length, with the short, deep profile typical of the genus. The fin counts run to 14–17 dorsal spines and 9–12 soft dorsal rays, with three anal spines and 8–9 anal soft rays; there are 27–30 scales along the lateral line. The single most useful internal character separating it from its relatives is the gill-raker count, with roughly 12–17 rakers on the lower limb of the first arch. The common-name clue is in the epithet: nigripinnis means 'black-finned', and Guichenot's specimens showed dark, blackish-brown fins. Live and preserved fish are generally marked with scattered black spots and blotches across the head and body, a peppered pattern rather than the bold vertical bars of many Coptodon. Sexual dichromatism is weak — FishBase records no marked colour difference between the sexes even when they are reproductively active, which is consistent with the genus's tendency toward monomorphism and the temporary, rather than permanent, pairings these fish form at spawning time. As in other Sarotherodon, the jaw teeth are fine and brush-like and yield slightly to the touch, the feature that gives the genus its name.
Habitat
Sarotherodon nigripinnis is a Lower Guinea coastal species, occupying the tropical belt roughly between 3°N and 7°S along the Atlantic seaboard of west-central Africa. The nominate subspecies holds the coastal zone of Gabon and Equatorial Guinea; the southern dolloi form occurs from the lower Kouilou in the Republic of the Congo down to the Congo estuary. Across this range it is fundamentally an estuarine fish. FishBase characterises it as a demersal, freshwater-and-brackish species that prefers brackish water but is regularly found in fresh water at low tide, when the salt wedge retreats and the tidal river reaches freshen — a daily oscillation between salinities that the fish moves through rather than avoids. Its preferred habitats are the lagoons, mangrove-fringed estuaries and lower river courses of the region, the kind of warm, soft, often tea-coloured coastal waters that characterise the Lower Guinea drainages. The lower Kouilou catchment that anchors the southern populations sits within the Ogooué–Nyanga–Kouilou–Niari freshwater ecoregion, a coastal-rivers province known for its high endemism. No precise in-situ chemistry has been published specifically for this species, but the brackish-to-fresh estuarine setting implies a wide, fluctuating salinity envelope and the warm, low-mineral, mildly acidic-to-neutral fresh water typical of equatorial coastal Africa; depth is shallow, the fish living in the few metres of water of lagoons and tidal channels.
Feeding
Like the rest of the Sarotherodon line, Sarotherodon nigripinnis is a low-trophic-level omnivore that grazes and filters rather than hunts. FishBase places its trophic level at about 2.3, near the bottom of the food web, and the genus's fine, flexible brush-like dentition is the dental signature of a fish that works over soft, fine material — algae, detritus, diatoms, plant fragments and the small invertebrates entrained in them — rather than seizing larger prey. Detailed gut-content work has not been published for this species specifically, but its better-studied sister, the black-chinned tilapia Sarotherodon melanotheron, is documented as a microphagous feeder taking diatoms, detritus, phytoplankton and fine organic matter in West African estuaries, and Sarotherodon nigripinnis can reasonably be read as filling the same detritivore-grazer guild in the Lower Guinea coastal systems. In the estuarine community it is one of the resident herbivore-detritivores that convert mangrove and algal production into fish biomass, a role that also makes the genus important to local subsistence and brackish-water aquaculture across the region.
Mating
Sarotherodon nigripinnis forms only temporary pair-bonds at spawning time; outside the brief reproductive episode the sexes are not strongly differentiated and there is no marked breeding dress. FishBase notes that the species shows no marked sexual dichromatism even when sexually active and that the pairings established during reproduction are transient. This fits the genus's reproductive grammar, which sits between the lek-and-leave maternal mouthbrooding of Oreochromis and the durable substrate-guarding pairs of Coptodon: Sarotherodon males do much or all of the brood care, and the bond between a male and female lasts only as long as it takes to get the clutch fertilised and into the incubating parent's mouth. In the southern dolloi populations the male's pre-spawning behaviour is more elaborate than simple courtship — he prepares a nest on the bottom (see Breeding) and defends it, so that pair formation is organised around a male-held nest site rather than a neutral arena. Courtship and the precise spawning sequence of the nominate Gabonese form have not been described in detail in the literature, and what is reliably documented is mostly the post-spawning incubation behaviour.
Breeding
Sarotherodon nigripinnis is a mouthbrooder, and the brooding is performed by the male — FishBase records simply that 'males carry eggs', the diagnostic Sarotherodon trait that separates the genus from the maternal Oreochromis. In the southern subspecies dolloi the sequence is unusually two-staged: the male first constructs a nest and the eggs are laid and fertilised there, after which he takes them up to incubate orally. The incubation period lasts about 14 days, after which the newly released young are retrieved in the mouth — a detail recorded for the species in which the female gathers up the just-emerged fry — and the juveniles become independent at roughly four weeks. Published clutch sizes for this species are not available; among Sarotherodon and the related estuarine tilapias, paternal and biparental mouthbrooders typically carry comparatively modest broods of a few dozen to a few hundred relatively large eggs, the trade-off of mouthbrooding being fewer but better-protected offspring than the thousands a substrate-spawning Coptodon may lay. The nest-build-then-brood pattern and the male's central role in care make this one of the more behaviourally interesting of the coastal tilapias, and a useful illustration of how the Sarotherodon genus bridges substrate nesting and oral incubation.
In the aquarium
Sarotherodon nigripinnis is essentially never seen in the ornamental hobby. It is a coastal, estuarine food-fish of west-central Africa with no established place in the aquarium trade, and there is no body of hobbyist husbandry literature for it; what keeping experience exists comes from fisheries and aquaculture work on the genus rather than from home aquaria. Anyone who did encounter it would be dealing with a brackish-water tilapia, not a soft-water blackwater cichlid: the right setup would be a large tank — this is an 7 in fish that needs swimming room and grows territorial when spawning — with a sand or fine substrate, salt added to give brackish conditions (the fish naturally moves between brackish and fresh, so it tolerates a range, but it does best with some salinity), warm tropical temperatures in the mid-to-upper 20s °C, and strong filtration to cope with a hearty omnivore's appetite. Diet is undemanding: as a detritus-and-algae grazer it would take vegetable-based and spirulina foods, sinking pellets and the usual frozen fare. Tankmates would need to be robust brackish-tolerant species rather than delicate community fish, and tilapia-typical digging and breeding-season aggression should be expected. In short, it is a fish to admire for its biology rather than one to seek out for a display tank, and the honest summary is that it is a fisheries species kept, if at all, only in a research or food-production context.
Conservation
Sarotherodon nigripinnis has not been assessed by the IUCN: a live check of the Red List returns no published assessment, and FishBase likewise carries its status as Not Evaluated, with no CITES or CMS listing. That absence reflects how little dedicated study the species has received rather than any evidence of either security or decline. The general outlook for the genus is reassuring — FishBase rates the species' resilience as high, with a minimum population doubling time under fifteen months and a low fishing-vulnerability score — and as a salinity-tolerant estuarine generalist it is less exposed than the narrow-range freshwater endemics of the same rivers. The real pressures on its range are habitat-level rather than species-specific: the Lower Guinea and Congo-estuary coastal systems face mangrove clearance, port and oil-industry development, pollution and sedimentation, and growing fishing effort, all of which bear on the brackish lagoons and tidal reaches this tilapia depends on. Until a formal assessment is made, the species is best regarded as presumably secure but genuinely under-studied, and its status should be read against the broader degradation of west-central African coastal wetlands.