Taxonomy & naming
The species was described by the Costa Rican-based ichthyologist William A. Bussing in 1974, originally in the genus Cichlasoma (later treated under Amphilophus and Astatheros), from the Pacific-slope rivers of southeastern Costa Rica. The epithet diquis refers to the Diquís — the indigenous name for the Grande de Térraba region of southern Costa Rica and its river system. The species was transferred to the new genus Cribroheros when Říčan and colleagues (2016) restricted Astatheros to its single Pacific type species and erected Cribroheros for the substrate-sifting heroines. Cribroheros belongs to the heroine cichlids (tribe Heroini), the genus name referring to the sieve-like sifting feeding of the group. It is one of the small southern Cribroheros allied to Cribroheros altifrons, with which it shares the Pacific-slope drainages of southern Costa Rica.
Morphology
Cribroheros diquis is a small cichlid, FishBase reporting a maximum of about 5.5 in SL. It has the moderately deep, robust body of the small southern Cribroheros, with a silvery-grey to olive or tan ground crossed by a row of dark blotches forming a broken midlateral line, a dark caudal-base spot, and barring that strengthens with mood and breeding condition; fine spangling and reddish fin margins appear in good colour. The mouth is sub-terminal, suited to sifting soft substrates. It is distinguished from its close relatives by details of coloration, body proportions and meristics given in the original description and by its Pacific-Térraba range. Sexual dimorphism follows the heroine pattern: mature males grow somewhat larger with more produced, pointed dorsal and anal fin tips, while ripe females are rounder-bodied and may show more contrasting markings when breeding.
Habitat
Cribroheros diquis is endemic to the Pacific slope of southeastern Costa Rica, centred on the Grande de Térraba (Diquís) drainage and adjacent Pacific rivers of the region. It inhabits warm lowland and foothill rivers and their pools and slower reaches, over substrates of sand, mud and gravel where it can sift for food, among rock and submerged wood. FishBase cites a broad temperature tolerance of roughly 73–91 °F, consistent with the warm lowland rivers of the southern Pacific versant. Its range overlaps that of the related Cribroheros altifrons in the same drainages; together they are characteristic small cichlids of the southern Costa Rican Pacific slope.
Feeding
Cribroheros diquis is a benthic omnivore and substrate-sifter with a notably low trophic level — FishBase places it near 2.6, among the most herbivore- and detritivore-leaning of the genus. Its recorded diet is insects, seeds and fruit, taken by sifting the soft bottom and gleaning fallen plant material; like its congeners it takes mouthfuls of sediment and sorts out the edible fraction in the winnowing manner that gives the genus its name. The sub-terminal mouth suits this bottom-oriented, partly frugivorous diet. In its river communities it functions as a small generalist forager of the substrate and the fallen-fruit and seed resource of the riparian zone.
Mating
As a heroine cichlid, Cribroheros diquis is a monogamous, biparental species that pairs and defends a joint breeding territory. Pair formation follows the standard cichlid courtship — lateral display, fin-flaring, jaw contact and cooperative cleaning of a spawning surface — with the pair intensifying in colour and becoming territorial as spawning nears. As a small species it is only moderately aggressive, but a bonded pair defends its patch firmly during the breeding cycle. Pairs select and clean a hard surface in advance of spawning.
Breeding
Cribroheros diquis is a biparental open substrate spawner. The female lays a clutch of adhesive eggs on a cleaned hard surface, and both parents share extended care: the female tends and fans the eggs while the male guards the territory, the roles converging as the brood develops; once free-swimming the fry are guarded as a school by both parents, who lead them over the soft bottom where they begin to forage. Clutch sizes in so small a fish are modest by genus standards. Wild breeding behaviour is not exhaustively documented, but it follows the well-established biparental-substrate-spawner pattern of the group.
In the aquarium
Cribroheros diquis is an uncommon aquarium fish, kept mainly by specialists in southern Central American cichlids. Its small adult size means modest space requirements — a tank of around 40–65 US gal suits a pair, with more for companions. It is adaptable in temperature given its broad natural range (about 73–86 °F is a sensible aquarium band) and does best in neutral to moderately alkaline water with good filtration and regular water changes. As a substrate-sifter it should be given a bed of fine sand, which lets it feed naturally and spares its gills the abrasion of gravel; furnish with rock and driftwood forming broken sight-lines and a flat stone as a spawning site, with hardy anchored plants. As a small, moderately aggressive species it mixes reasonably with other robust fish of similar size and water needs, with breeding pairs given space at spawning time. Feeding should reflect its partly frugivorous natural diet — a quality sinking pellet plus frozen and live invertebrate foods and a generous share of vegetable and plant-based matter. The main husbandry note is to provide sand and a varied, plant-inclusive diet.
Conservation
Cribroheros diquis is a Pacific-slope endemic of southeastern Costa Rica, and that restricted distribution is the central conservation consideration for the species. Its formal IUCN Red List status was not clearly established in the sources consulted (it is treated here as Not Evaluated pending verification), but as a small-range endemic of the Térraba and adjacent Pacific drainages it warrants precautionary attention. Those lowland river systems are exposed to the region's familiar pressures — deforestation and conversion to plantation agriculture (pineapple, oil palm), water extraction, sedimentation, agro-chemical runoff and introduced species — and the long-discussed prospect of large hydroelectric development on the Térraba would, if realized, substantially alter the species' core habitat. It carries no CITES listing. As with all of the genus, the health of its river system is the key determinant of its long-term status.