Taxonomy & naming
Crenicichla tesay was described in 2008 by the Argentine ichthyologists Jorge R. Casciotta and Adriana E. Almirón, in the December 2008 issue of the Revue suisse de Zoologie (volume 115, pages 651–660); the binomial is often cited with the volume year 2009, as FishBase and the Catalog of Fishes do. It was the third pike cichlid named from the río Iguazú basin, after Crenicichla iguassuensis Haseman, 1911 and Crenicichla yaha Casciotta, Almirón & Gómez, 2006. The holotype (MACN-ict 9016, a 4.5 in-SL specimen) was taken in arroyo Verde, a stream in the Iguazú basin of Misiones Province, Argentina, with a large type series drawn from neighbouring tributaries. Casciotta and Almirón diagnosed the species within the temperate-southern Crenicichla lacustris species group by a serrated preopercle, a low scale count (48–59 in the E1 row), a conspicuous suborbital stripe, four to six blotches below the upper lateral line with the rearmost running onto the caudal peduncle, and flanks scattered with small irregular dots but no vertical bars. A 2015 reappraisal by Piálek, Dragová, Casciotta, Almirón and Říčan refined the picture considerably: working with fresh field material they showed that the four endemic Iguazú pikes form a small sympatric flock within the Crenicichla mandelburgeri complex, each tuned to a different feeding niche, and that populations earlier reported as Crenicichla yaha from the Iguazú actually belong to Crenicichla tesay — true Crenicichla yaha being restricted to the neighbouring Urugua-í stream. They also placed Crenicichla tesay as the small-mouthed, mollusk-collecting member of the flock. The broader genus Crenicichla has since been the subject of generic revision (Varella and colleagues, 2023) that would partition the South American pike cichlids; this atlas retains the long-established name Crenicichla tesay pending wider adoption.
Morphology
Crenicichla tesay has the elongate, cylindrical, big-eyed build typical of pike cichlids, the body depth going about four to five times into the standard length and the head only slightly deeper than wide. What sets it apart from its Iguazú relatives is the front of the fish: the snout is short and bluntly pointed, the mouth small, and the jaws roughly even (isognathous) or with the lower jaw only faintly projecting — a markedly less predatory profile than the long-jawed, prognathous pikes alongside it. The defining internal feature is the lower pharyngeal (throat) tooth plate, which is heavily built and bears several rounded molariform teeth along its suture and rear edge, a crushing mill for hard-shelled prey. Reported size depends on the source: FishBase lists about 4.5 in standard length, but the type series examined in the original description ran from 2 in up to a 10 in-SL specimen (about 10 in), so well-grown wild fish reach a substantially larger size than the FishBase figure suggests. Colour in life is a grey ground (usually in males) to greenish or yellowish (usually females), thoroughly peppered with small irregular black dots; about six dark midlateral blotches run along the flank, the last continuing onto the tail base, and a black ocellated spot sits high on the caudal-fin base. The signature marking is the suborbital stripe that gives the fish its name — wide, rather short, and broken up into a row of separate black dots that trail down the cheek like a smudged tear-streak. Sexual dimorphism is subtle outside breeding (the original describers noted no obvious dichromatism in preserved fish), but ripe females develop a striking dorsal fin marked by a black band edged in white along its rear portion.
Habitat
The río Iguazú rises in the Serra do Mar of southern Brazil and runs west for some 1,199 mi before joining the Paraná, its final stretch forming the Argentina–Brazil border. About 20 mi above that junction the river drops 256 ft over the Iguazú Falls — a barrier to fish movement since the Oligocene–Miocene and the reason the Iguazú carries a depauperate but highly endemic fauna, roughly 60 percent of it found nowhere else. Crenicichla tesay lives entirely above the falls, in the basin's tributary streams and main channel; the 2015 fieldwork found it common and dominant throughout, from the Argentine province of Misiones upstream into the Brazilian state of Paraná. The original collectors described its streams as fairly shallow, averaging about 31.5 in deep, with clear, rapidly flowing water broken by small falls and pools, bottoms of mud, sand and (mostly) stones, and only scattered submerged plants. As a snail-eater it favours stony bottoms where mollusks live. These are subtropical waters that cool seasonally well below the tropical Amazon norm, and the Iguazú is a soft, clear, near-neutral system; no fine in-situ chemistry was published with the description, so the chemical figures below are reasonable subtropical-stream estimates rather than measured values for this species.
Feeding
Within the small Iguazú pike-cichlid flock the four endemic species divide the available food, and Crenicichla tesay took the mollusk niche. Its short jaws, small mouth and — above all — its massive lower pharyngeal plate studded with rounded molariform teeth are the toolkit of a durophage: a fish that gathers snails and other hard-shelled invertebrates and crushes them in the throat. The 2015 study explicitly identified it from field observation, stomach contents and tooth morphology as a 'picker' taking a substantial amount of hard-shelled mollusks, contrasting it with its long-jawed, fish-and-large-prey-eating relatives in the same streams. This is a notable departure from the pike-cichlid stereotype of a lurking ambush piscivore; Crenicichla tesay instead works the stony substrate methodically for shelled prey, a specialization that lets several closely related pikes coexist in one small, isolated drainage.
Mating
No detailed account of courtship or pair formation in Crenicichla tesay has been published — it is a recently described, range-restricted fish of remote subtropical streams that has attracted study chiefly as a member of an endemic species flock rather than as an aquarium subject. What can be said rests on what is documented for the genus and on the one clear breeding-linked clue in the species itself: ripe females develop a boldly marked dorsal fin, with a black band edged in white. Across Crenicichla, pike cichlids are territorial, pair-forming substrate breeders in which a male and female establish and jointly defend a nest site, the female typically the more conspicuously coloured of the pair as spawning nears. The brightened breeding dorsal of female Crenicichla tesay fits that pattern and is presumably a courtship and pair-bonding signal. Beyond this, the specifics of its mating behaviour remain undocumented in the wild.
Breeding
Spawning has not been described for Crenicichla tesay, in the wild or in captivity. Like other pike cichlids it is expected to be a biparental substrate or cave spawner — laying adhesive eggs on a sheltered hard surface (a rock face, crevice or cavity) that both parents then guard and fan, with the female tending the clutch and the male defending the territory, and both shepherding the free-swimming fry afterward. The female's seasonally intensified dorsal-fin pattern is consistent with this guarding-pair strategy. No clutch count has been published for the species; small to mid-sized Crenicichla of this type generally produce broods on the order of a few hundred eggs, which is the best genus-typical expectation until the species itself is bred and documented. Spawning is presumably keyed to the warmer, higher-water months of the subtropical year, as in other Iguazú-basin fishes.
In the aquarium
Crenicichla tesay is essentially an unkept fish in the hobby. It is a recently described endemic of a remote, internationally shared and partly protected basin (the Iguazú National Parks of Argentina and Brazil sit within its range), it has no established place in the ornamental trade, and there is no body of hobbyist experience to draw on — so this section is necessarily general rather than a tested husbandry guide.
If it were kept, the requirements would follow from its biology. This is a stream pike of clear, well-oxygenated, briskly flowing subtropical water, so a long tank with strong filtration, real current and high oxygen would matter more than volume per se; an adult of 8 in or more needs a footprint of at least 47 in. Crucially, it is a cool-water fish by cichlid standards — the Iguazú above the falls cools markedly in the southern winter — so it should not be kept at the high tropical temperatures suited to Amazon cichlids; a seasonally variable mid-range is more appropriate. The substrate should be sand and rounded stone with plenty of rockwork and crevices for cover and potential spawning sites. Because it is a snail-crusher rather than a fish-hunter, its diet would centre on hard-shelled and meaty invertebrates — snails, shellfish, and other firm frozen foods — rather than feeder fish.
Temperament would be the usual pike-cichlid calculus: territorial, especially when breeding, and best given space and sightline breaks, though its small mouth makes it less of a threat to tankmates than the long-jawed predatory pikes. None of this has been verified for this particular species; anyone encountering it should treat it as a sensitive, cool-water specialist and document what they learn.
Conservation
Crenicichla tesay has not been assessed on the IUCN Red List; it carries no published global category, so its status is best recorded as Not Evaluated. (Some aggregator pages list it as 'Least Concern', but no live Red List assessment for the species could be located, and that label appears to be inherited rather than a genuine evaluation.) The 2015 fieldwork found it common and dominant throughout the upper Iguazú, which is encouraging, and part of its range lies within the Iguazú National Park system of Argentina and Brazil. Against that, it is a narrow-range endemic confined to a single basin above a natural barrier, and the río Iguazú is among the most heavily dammed rivers in the region — a cascade of hydroelectric reservoirs has flooded long reaches of the main channel and its tributaries, exactly the stony, flowing, mollusk-bearing habitat this specialist depends on. Its sister species Crenicichla yaha, from the adjacent Urugua-í stream, has not been seen since that stream was dammed in 1989, a sobering illustration of how vulnerable these small Iguazú-system endemics are to impoundment. A formal assessment of Crenicichla tesay would be worthwhile.