Taxonomy & naming
The species was described by the American naturalist Edward Drinker Cope in 1872, in his account 'On the Fishes of the Ambyiacu River' published in the Proceedings of the Academy of Natural Sciences of Philadelphia. The original combination was Saxatilia anthurus, and the type locality is the Río Ambyiacu — modern Ampiyacu, a left-bank tributary of the Amazon in northeastern Peru near Pebas. Three syntypes survive in the Academy of Natural Sciences of Philadelphia (ANSP 9074–76); Böhlke catalogued the types in 1984 and Sven Kullander discussed them in his 1986 monograph on the cichlids of the Peruvian Amazon, which redescribed the species with a full diagnosis, distribution and illustrations. Within the large genus Crenicichla the species belongs to the saxatilis group, the assemblage of small to medium pike cichlids that share the characteristic juvenile longitudinal stripe and an ocellated caudal spot; in the older literature it sits alongside lucius, proteus and semicincta as the western-Amazon members of that complex, and its morphometric separation from neighbours such as proteus is famously slight. In 2023 Varella, Kullander, Menezes, Oliveira and López-Fernández published an integrative phylogenetic revision of the pike cichlids that split Crenicichla into several genera and resurrected the genus Saxatilia for the saxatilis group; under that classification the fish becomes Saxatilia anthurus (Cope, 1872), the arrangement now followed by Eschmeyer's Catalog of Fishes and the Cichlid Room Companion. Both names refer to the same animal, and major databases including FishBase and the IUCN Red List still list it as Saxatilia anthurus.
Morphology
Saxatilia anthurus is a typical pike cichlid in shape: an elongate, nearly cylindrical, slightly compressed body with a long head, a large oblique mouth and the dorsal and anal fins set well back to drive the short, darting lunge of an ambush hunter. FishBase gives a maximum size of 9 in standard length, putting it among the smaller-to-medium members of the genus; most aquarium and wild specimens are considerably shorter. Ground colour is an olive to greyish brown over the back, paler below, overlaid in the saxatilis-group pattern by a dark lateral band that runs from the snout through the eye to the tail and a dark ocellated humeral (shoulder) spot. The most distinctive feature is the one Cope chose for the name: the caudal fin is richly coloured — his account described it as deep crimson fading to purple at the base, crossed by a dark central shade and stippled with small oval pink spots set between the rays — and carries an ocellus. Juveniles wear the bold black longitudinal stripe shared across the group, which breaks up into mottling and barring as the fish matures. Sexual dimorphism follows the genus pattern: females are rounder-bellied when in condition and, as in close relatives of the saxatilis group, develop ocelli (eyespots) in the dorsal fin, while males grow larger, are more slender and intensely coloured, and tend to bear the longest fin extensions.
Habitat
The species is restricted to the western Amazon, with records spanning the Ucayali, Huallaga, Putumayo, Napo and upper Amazon (Marañón–Solimões) drainages. Eschmeyer's Catalog of Fishes gives its distribution as the Amazon and Orinoco basins of Colombia, Ecuador and Peru; FishBase confines it to the Amazon basin. It is, in Kullander's and FishBase's words, a fish of small forest streams — the shaded, slow-to-moderate creeks and igarapés of the lowland rainforest rather than the open main rivers — where it lives among submerged wood, leaf litter and bankside roots that suit an ambush predator. In-situ chemistry has not been published as a dedicated study, but the species belongs to the soft, warm, often tea-stained waters of the upper Amazon lowlands; FishBase's compiled tolerances give a pH range of about 6.0–8.0, hardness around 5–19 dH, and a tropical temperature band of roughly 75–82 °F. As a forest-stream fish it occupies shallow water, generally within the top metre or two of these small channels rather than deep river habitat.
Feeding
Like all pike cichlids, Saxatilia anthurus is a predatory ambush feeder built around a large mouth and an explosive forward lunge, hunting from cover among wood and leaf litter. Its diet is broader than the term piscivore implies: FishBase records it feeding on plant debris, insect debris and larvae, and fish larvae, which places it as a small generalist carnivore that takes whatever invertebrates and small fish its forest-stream habitat offers, with an estimated trophic level near 2.8. Aquatic insect larvae and other benthic invertebrates make up the bulk of the diet, supplemented by small fishes and incidental plant and organic material picked up while foraging over the substrate. In the stream community it is a mid-level predator of the smaller fishes and invertebrates rather than a top piscivore — a reflection of its modest adult size compared with the metre-long Crenicichla and Lugubria of the main rivers.
Mating
Reproductive behaviour has not been documented in the wild for this particular species, and what is known is inferred from the well-studied saxatilis-group pike cichlids it most resembles. These fish form monogamous pairs that hold a defended territory, with courtship centred on a chosen cave or sheltered crevice; pair formation involves mutual display, lateral spreading of the brightly coloured fins, and the gradual establishment of a bond before spawning. The dorsal-fin ocelli that females of the group develop are thought to function as signalling marks during this courtship and brood care. Territoriality intensifies sharply around breeding, when the pair will drive off conspecifics and other fish from the immediate area of the nest. As in the genus generally, pair bonds can be tense, and an unready or mismatched fish may be harried by its partner.
Breeding
No wild spawning of Saxatilia anthurus has been described in the literature, and FishBase carries no fecundity figures for the species; the account here is drawn from its close relatives in the saxatilis group, which are the standard model for small western-Amazon pike cichlids. These are biparental cave (substrate) spawners: the female attaches a clutch of adhesive eggs to the roof or wall of a sheltered cavity — a rock crevice, a hollow under wood, or a length of submerged tube — and tends and fans the eggs while the male patrols and defends the surrounding territory. Reported clutches for comparably sized congeners typically run from roughly 100 to several hundred eggs. After hatching, the wrigglers are moved to pits and the free-swimming fry are guarded by both parents as a tight school, herded back to cover at any disturbance, with care continuing for some weeks. Soft, warm water and a rise in temperature with the onset of the rainy season are the usual triggers in this group. Until the species itself is bred and documented, these figures should be read as genus-typical inferences rather than measured values for anthurus.
In the aquarium
Saxatilia anthurus reaches Peruvian exporters under the local name añashua and turns up in the trade only occasionally, usually as a mixed or misidentified member of the saxatilis/proteus group rather than as a named import — the morphometric overlap among these western-Amazon pikes means trade fish are routinely confused. It is, by pike-cichlid standards, a manageable species: at a maximum of around 8.5 in it is far smaller than the large-river Crenicichla, and a single adult or a settled pair can be kept in a tank of roughly 47 in length (about 65 US gal), with more room strongly preferred for a pair so a harried fish can escape.
The tank should recreate a shaded forest stream — a sand or fine-gravel bottom, generous driftwood and root tangles, leaf litter, and several caves or lengths of pipe to serve as territories and potential spawning sites. Dim lighting and cover bring out the fish's colour and reduce its natural shyness. Water should be soft to moderately hard and warm, in the range FishBase reports for the species: pH around 6.0–7.5, temperature about 75–82 °F, with clean, well-filtered, gently moving water and regular partial changes, as pike cichlids are sensitive to accumulated waste.
Feeding is straightforward for a predator: it takes live and frozen foods — bloodworm, other insect larvae, small earthworms, river shrimp and the like — and most specimens can be weaned onto good-quality sinking carnivore pellets, though it should not be kept on dried food alone. Live or frozen meaty foods produce the best colour and condition.
Temperament is the usual pike-cichlid caution rather than alarm: it is predatory and will eat any tankmate small enough to swallow, and it is territorial, especially when paired or spawning, but it is not the tank-wrecking brawler that the giant species can be. Suitable companions are robust, similarly-sized or larger characins, larger catfish and other fish too big to be prey and not so aggressive as to bully it. Keeping two unsexed adults together in a small tank is the common mistake — without space and cover, intraspecific aggression can be lethal. It is a rewarding fish for a keeper who wants the pike-cichlid character without a six-foot tank, provided its identity and modest needs are understood.
Conservation
The IUCN Red List assesses Saxatilia anthurus as Least Concern (assessed 9 October 2014, published 2016; assessors H. Ortega Torres, P. Jimenez-Prado, F. Villa-Navarro and P. Arguello). The assessment reflects a relatively wide distribution across several western-Amazon drainages in Peru, Ecuador and Colombia and the absence of any identified major threat to the species as a whole; it carries no CITES listing and is regarded as harmless to people. It is taken in small numbers for the ornamental trade but not at a level flagged as a population concern. Like all fishes of the upper Amazon lowlands, it lives against a backdrop of accelerating pressure on the basin's freshwaters — deforestation of the headwater forests it depends on, road-building, mining and its associated pollution, and the damming and hydrological alteration of Andean-foothill rivers — none of which is documented as a present danger to this particular species but all of which bear on the small forest streams it inhabits.