Taxonomy & naming
Crenicichla cyanonotus was described by the American naturalist Edward Drinker Cope in 1870, in the Proceedings of the American Philosophical Society, from a single specimen collected in the upper Marañón River near Pebas, Peru. That holotype — ANSP 9078, held at the Academy of Natural Sciences in Philadelphia — remains the unique name-bearing specimen. Cope placed the fish directly in Crenicichla, the genus Johann Jakob Heckel had erected in 1840 for these pike-like cichlids. For a time the species was shuffled into Batrachops, a genus several authors used for pike cichlids with blunter heads and certain dentition differences; Ortega and Vari (1986) listed it as Batrachops cyanonotus. That arrangement did not last: Sven Kullander folded Batrachops back into Crenicichla and redescribed cyanonotus in his 1986 monograph on the cichlids of the Peruvian Amazon, and the Catalog of Fishes recognizes it today as a valid species, Crenicichla cyanonotus Cope 1870. It sits within the Crenicichla saxatilis group, by far the largest division of the genus, which now holds more than two dozen described species spread across lowland South America. The species' boundaries are not fully settled. A mitochondrial-DNA phylogeny by Chuctaya and colleagues (2022) found that material currently called Crenicichla cyanonotus carries a very wide distribution across the southwestern Amazon, including the upper Madeira, and cautioned that the specimens they sequenced may not represent Cope's nominotypical western-Amazon fish — so the true composition of the species awaits a modern revision.
Morphology
Crenicichla cyanonotus is a comparatively modest pike by the standards of a genus whose giants exceed 15.5 in. FishBase records a maximum of about 6 in standard length, placing it among the medium-small members of the saxatilis group rather than the dwarf pikes or the large strigata-group fish. The body plan is the familiar pike-cichlid template: long, cylindrical and laterally compressed toward the rear, with the dorsal and anal fins set far back and a head drawn out into a broad, deeply cleft mouth — the protrusible, tooth-studded jaws of an animal that swallows prey whole. Coloration in life is poorly documented for this particular species; preserved material is dominated by browns and greys with the dark lateral markings typical of the group. The epithet itself preserves the one feature Cope singled out: a blue tint at the base of the dorsal fin in his single specimen. As in most saxatilis-group pikes, sexual dimorphism is expected to follow the genus pattern — ripening females developing a swollen, reddish belly during the breeding season and, in many group members, a distinctively ocellated or boldly marked dorsal fin, while males grow somewhat larger and may carry longer fin extensions. The exact dimorphic signals of Crenicichla cyanonotus have not been described in detail, so these are inferred from its close relatives rather than recorded from the species itself.
Habitat
The species is a fish of the western Amazon lowlands. The type locality lies on the upper Marañón near Pebas in northeastern Peru, and the recorded range extends through the southwestern parts of the basin: Peru, the Brazilian states of Acre, Amazonas, Mato Grosso, Pará and Rondônia, and into Bolivia. This places it largely within the Amazonas Lowlands freshwater ecoregion, which gathers the Amazon floodplain together with the Marañón, Ucayali and parts of the Madeira drainage. Like other saxatilis-group pikes it is a benthopelagic fish of warm lowland waters, favouring the kind of structured, slower habitats the genus prefers — vegetated margins, backwaters and the edges of streams and rivers rather than open current, with brooding adults tending to retreat to quiet bays and side-arms. FishBase gives a preferred temperature window of roughly 75–81 °F and a pH range spanning about 5.5 to 8.0, with very soft to moderately hard water (from around 1 °dH upward); these figures reflect the broad chemical tolerance pike cichlids show across the three Amazonian water types — black, white and clear. No precise in-situ chemistry or a documented depth band has been published for Crenicichla cyanonotus specifically; as a shallow-water river fish it occupies the upper few metres of its habitat, but the exact figures are not on record.
Feeding
Crenicichla cyanonotus is a predator. The entire genus is built around ambush piscivory and invertivory: an elongate body for acceleration from cover, a large protrusible mouth, and the patience to lie among roots, leaf litter or PVC-tube-like crevices and dart out at passing prey. Gut analyses of Amazonian pike cichlids by Knöppel (1970) found their diet dominated by insects and insect larvae, shrimp and small fish, with the larger species taking proportionally more fish; intriguingly, a notable fraction of plant material also turns up in some stomachs. FishBase estimates a trophic level around 3.3 for Crenicichla cyanonotus, consistent with a mid-sized predator that takes a mix of aquatic invertebrates and small vertebrates rather than a pure fish-eater. At under 6 in it is too small to be a specialist piscivore on the scale of its giant congeners; in its community it functions as a lurking generalist carnivore of the marginal and benthic zones, snapping up invertebrates and any fish small enough to fit the gape.
Mating
Reproductive behaviour has not been documented for Crenicichla cyanonotus directly, but the saxatilis group to which it belongs is reproductively well studied in aquaria and the pattern is consistent. Pike cichlids form monogamous pairs, and pair formation is the delicate phase: aquarists describe a near-instant mutual acceptance — "love at first sight" — when two ripe, healthy, well-matched fish are introduced, or violent rejection when they are not, since in a tank the loser cannot simply swim away. Courtship is female-led and strikingly convergent with West African kribs (Pelvicachromis): the ripening female develops a swollen cherry-red belly and performs a head-down shaking dance, swinging her body first one way then the other to display the swollen abdomen to the male, who plays a more passive role. The female establishes and runs the show around a chosen spawning cavity while the male patrols the territory. Pikes are territorial and can be severely aggressive toward conspecifics outside an accepted pair bond, which is why captive pairings are managed so carefully; once a bond settles, the pair is typically devoted and comparatively peaceful with each other.
Breeding
No wild or captive spawning of Crenicichla cyanonotus has been published, so its breeding is described from the well-documented behaviour of its saxatilis-group relatives, which it can be expected to follow closely. These pikes are biparental cave spawners. The female attaches eggs inside a secluded cavity — under reports for related species, an upturned flowerpot with an enlarged entrance, a length of PVC pipe, a coconut shell or the recess of a bogwood tangle — and the eggs are hung from the surface by short adhesive filaments, an attachment style unusual among Neotropical cichlids and reminiscent, again, of the West African dwarf cichlids. Clutch size in the medium-sized group members runs widely with the size of the pair: for the closely comparable Crenicichla proteus, Kerson recorded spawns of roughly 50 to 500 eggs, a figure that brackets the genus-typical expectation for a pike of this size. The female tends and fans the eggs while the male defends the perimeter. In related species the eggs hatch in about three days and the fry become free-swimming roughly two days later, after which both parents guard the brood diligently — pike cichlids are noted, despite their predatory build, as gentle and attentive parents that may shepherd their young for weeks to months. The fry are large enough to take newly hatched brine shrimp from the outset and grow quickly.
In the aquarium
Crenicichla cyanonotus is not a commonly traded fish in its own right; most saxatilis-group pikes reach hobbyists as mixed wild imports, and husbandry advice for it rests on the broad, well-established body of pike-cichlid keeping rather than species-specific experience. At under 6 in it is one of the more manageable pikes, but the genus rules still apply. A single fish or a settled pair can be kept in a tank of around 47 in length; the decisive feature is not raw volume but cover. Pike cichlids feel secure — and are far less aggressive — when given abundant hiding places: lengths of PVC pipe, driftwood tangles and dense planting that break sightlines. The classic recommendation is to start with a group of similarly sized juveniles and grow them out together with one tube or cave per fish, then let a pair form, because mismatched or crowded adults can quickly turn lethal toward one another. Water should be warm (the mid-to-upper 20s °C) and, above all, clean: these are heavy eaters with a correspondingly heavy waste load, so powerful filtration and regular substantial water changes (25–50%) are standard, and good aeration matters because pikes demand well-oxygenated water. Chemistry is forgiving — somewhere in the soft-to-moderately-hard, mildly acidic to slightly alkaline range mirroring FishBase's pH 5.5–8.0 — though soft, acidic blackwater conditions are wise for any breeding attempt. Some pikes are prone to head-and-lateral-line erosion linked to poor water quality, a further argument for diligent maintenance. Feeding is straightforward for a fish acquired young: juveniles take frozen and dried foods (bloodworms, krill, sinking pellets, prawn) readily, whereas large wild adults can be stubbornly fixed on live food and harder to wean. Tankmates should be robust, too large to be swallowed, and not delicate fin-nippers; the real incompatibility, as always with pikes, is intraspecific. Keep a divider or spare tank on hand when introducing potential pairs.
Conservation
The IUCN Red List assesses Crenicichla cyanonotus as Least Concern (assessed 30 November 2020 by R.G. Frederico, published 2023), with the population trend listed as unknown. The assessment reflects a wide distribution across the southwestern Amazon — Peru, Bolivia and several Brazilian states — and the absence of any identified species-level threat; the fish carries no CITES or CMS listing and is considered harmless to humans. As a widespread, adaptable predator of lowland waters it is far less exposed than the basin's many narrow-range endemics. The backdrop, however, is the broad and accelerating pressure on Amazonian freshwater systems: hydropower dams that fragment river connectivity from the Andes to the lowlands, deforestation, mining and altered flood-pulse regimes are documented as degrading aquatic habitats across the basin even where freshwater conservation remains comparatively neglected. None of these is recorded as a present danger to this particular pike, but they frame how its long-term status should be read — and the unresolved question of whether "Crenicichla cyanonotus" is one species or several means that any local form could prove more restricted than the aggregate range suggests.