Taxonomy & naming
Paretroplus gymnopreopercularis was described by the American ichthyologist John S. Sparks in 2008, in his monographic 'Phylogeny of the cichlid subfamily Etroplinae and taxonomic revision of the Malagasy cichlid genus Paretroplus' (Bulletin of the American Museum of Natural History 314: 124, figs. 55–56, pl. 1K). The holotype (UMMZ 247710, formerly UMMZ 239532) was collected northeast of the town of Mandritsara in the Amboaboa River near its confluence with the Mangarahara River, in the upper Sofia River basin of what was then Mahajanga (Majunga) Province, at an elevation of about 689 ft; a series of paratypes is held at the American Museum of Natural History and the University of Michigan Museum of Zoology. It has no synonyms — the name has stood as originally proposed since 2008. Paretroplus is one of the Etroplinae, the small Gondwanan relict subfamily that today survives only as the Malagasy dambas and a handful of cichlids in India and Sri Lanka (Etroplus and Pseudetroplus); molecular and morphological work places Paretroplus as sister to those Asian genera rather than to the African cichlids next door, a biogeographic signature of Madagascar's deep isolation. Within the genus, Sparks recovered gymnopreopercularis as the close relative of Paretroplus kieneri; the two form a distinctive pair set apart from the high-bodied 'true dambas' by their more elongate shape, the absence of vertical bars, and a blotchy, mottled rather than barred colour pattern. The two are difficult to tell apart and are easily confused, which is one reason the species went undescribed until 2008.
Morphology
This is a comparatively small, elongate Paretroplus — the type series reaches about 6 in in standard length, modest beside the disc-shaped dambas that can exceed 14 in. The body is fusiform and laterally compressed with a blunt, strongly convex predorsal profile, and the snout carries a fleshy pad that extends forward past the lips and down to partly cover the upper lip. Fin counts run to 17–19 dorsal spines and 13–15 dorsal soft rays, 8–10 anal spines and 11–13 anal soft rays, over 32–34 vertebrae; the multiple stout anal-fin spines are the family hallmark that separates any Paretroplus from every other native Malagasy cichlid, which carry only three. Coloration in life is an orangish-brown to golden-brown, with a weakly mottled, largely uniform 'chain-link' pattern produced by darkly pigmented scale margins — never the dark gray of its sister species kieneri, and without either the vertical bars or the horizontal stripes seen elsewhere in the genus. The diagnostic feature that gives the fish its name is hidden on the cheek: the preopercle is asquamate — naked, scaleless — whereas in kieneri it is fully scaled or scaled except along the ventral margin. Sparks also separates the two by the arrangement of the lacrimal and infraorbital bones around the eye. No external sexual dimorphism has been documented for this species; in several of its better-known congeners mature males develop intensified colour and males grow somewhat larger, but that has not been confirmed in gymnopreopercularis.
Habitat
Paretroplus gymnopreopercularis is endemic to Madagascar and, as far as is known, to a single short stretch of the Amboaboa River near its confluence with the Mangarahara, both tributaries of the upper Sofia River drainage in the north of the island. This is upland flowing water, not the turbid floodplain lakes favoured by the high-bodied dambas: the rivers here are shallow and clear, the current swift, broken into a succession of small cascades and riffles over a bed of rock and exposed boulders interspersed with sand. Within that fast water the species appears to keep to the deeper, more isolated standing pools rather than the riffles themselves. No in-situ chemistry has been published specifically for this fish, but the genus as a whole occupies warm, generally soft water spanning mildly acidic to alkaline conditions; conservation surveys of the same Amboaboa system, carried out for the syntopic Mangarahara cichlid, report near-neutral to slightly alkaline water around pH 7.5 with low hardness and warm temperatures, consistent with the broader Paretroplus pattern of pH roughly 6.5–8 and temperatures that often climb above 86 °F in the late dry season. Because the fish persists only in shrinking pools, its effective depth band is shallow.
Feeding
No direct diet study exists for Paretroplus gymnopreopercularis, so its feeding is read from the genus. Paretroplus are equipped with robust, molariform pharyngeal teeth — a crushing mill in the throat — and where gut contents have been examined (for example in the related Paretroplus maromandia, whose guts were packed with crushed shells) they prove to be specialist hard-prey feeders, taking small gastropods and other molluscs and grinding the shells to fragments. Most species are assumed to take a significant share of molluscs supplemented by algae and other plant and invertebrate material, making the genus broadly an omnivore with a durophagous (shell-crushing) bent. In its swift, rocky river Paretroplus gymnopreopercularis most plausibly works the boulder and sand substrate of its pools for snails and bottom invertebrates, with algae grazed from rock surfaces; its trophic level is estimated near 2.9. The shape of its head and the fleshy, protruding snout are consistent with a fish that picks and grubs at the substrate rather than one that hunts in open water.
Mating
The courtship and pair behaviour of Paretroplus gymnopreopercularis have never been observed — it has not been kept in aquaria anywhere outside Madagascar, and no field account of its breeding exists. What can be said comes from the genus, which is consistent enough to be informative. Paretroplus are monogamous, biparental fish that form pairs and defend a spawning site together; they are social outside the breeding season, often found in loose groups, but become territorial and can be markedly aggressive toward their own kind as they pair off. In its better-studied relatives a pair selects and cleans a site — a rock, a waterlogged branch, or a depression excavated in the substrate — and courts around it before spawning. Maturity in the genus comes relatively early for a cichlid of its size, at roughly 12 to 18 months. Whether gymnopreopercularis, as a rheophilic pool-dweller, behaves more like the open-substrate lake dambas or more like the cave-spawning river specialists of its own lineage is simply unknown.
Breeding
Breeding has not been documented for Paretroplus gymnopreopercularis in the wild or in captivity; the account here is genus-typical and explicitly inferred. All Paretroplus are monogamous substrate spawners that, in Madagascar, breed during the second half of the dry season, roughly August through October. They deposit adhesive eggs — large and salmon-to-orange in colour in the genus — onto a cleaned hard surface: lake and river-pool species generally spawn in the open on rock or wood, while the rheophilic members of gymnopreopercularis's own clade (Paretroplus nourissati and Paretroplus tsimoly) are cave spawners, so a sheltered crevice nest is plausible for this species too. Both parents share guarding and tending of the eggs and the resulting wrigglers and fry, fanning the clutch and removing fouled eggs. Clutch sizes and developmental timing have not been recorded for gymnopreopercularis specifically; among its captive-bred congeners, fry are slow-growing and notoriously dependent on a long, uninterrupted supply of live food in the first months. None of this has been confirmed for this particular fish, which remains one of only a couple of Paretroplus never spawned in an aquarium.
In the aquarium
For practical purposes Paretroplus gymnopreopercularis is not an aquarium fish. Together with Ptychochromis loisellei it is one of the very few members of the genus that has never been kept or bred outside Madagascar; there are no breeding reports, no hobby stock, and no realistic prospect of legitimate availability given its Critically Endangered status and tiny, protected range. It is described here only to set expectations honestly and to place the fish within its genus. Were it ever to enter managed conservation husbandry, the established Paretroplus template would apply: a large tank (well over 105 US gal for a group of adults), a single-species set-up to manage the genus's intraspecific aggression, fine sand with rock and wood for cover and spawning sites, well-filtered and frequently changed water kept warm (above about 75 °F, warmer to breed) and at or above neutral pH, and a diet built around invertebrates — snails especially, which suit the shell-crushing pharyngeal mill — supplemented with quality prepared and frozen foods and some vegetable matter. Keeping these fish in a group reduces the chronic aggression and improves the odds of natural pair formation. But all of that is extrapolation from its relatives; for gymnopreopercularis itself the honest statement is that no one has kept it, and its survival depends on its river rather than on the hobby.
Conservation
The IUCN Red List assesses Paretroplus gymnopreopercularis as Critically Endangered (criteria B1ab(iii,v)), assessed by J.S. Sparks and published in 2016, with a decreasing population trend. The category reflects an extremely small range — essentially the Mangarahara River and its tributary the Amboaboa, in the upper Sofia drainage — combined with continuing decline in both habitat quality and the number of mature individuals. The threats are the same ones that have made this catchment a byword for freshwater extinction risk: a cascade of small dams and weirs built on the lower Amboaboa to divert water to rice fields, which has throttled flow and dried long sections of river; deforestation across the basin, which drives erosion and silts up the pools and spawning grounds; recurrent drought; introduced exotic fishes; and fishing pressure on a fauna long prized locally as food. This is the very water in which the syntopic Mangarahara cichlid (Ptychochromis insolitus) was reduced to a literal handful of survivors and was nearly lost, prompting a 2013 international rescue appeal and the founding of the Fish Net Madagascar project to protect the Amboaboa basin's endemic fishes. Paretroplus gymnopreopercularis is far less studied than its celebrated tankmate and, having never entered captivity, has no conservation safety-net population; its fate is tied entirely to whether the Amboaboa keeps flowing.