Taxonomy & naming
The yellow mojarra was described by the Austrian ichthyologist Franz Steindachner in 1878 as Petenia kraussii, in a brief diagnosis published in the proceedings (Anzeiger) of the Vienna Academy of Sciences; he illustrated and described it more fully the following year. The type locality is Ciénaga, on the Río Magdalena in Colombia, and the species was founded on a series of syntypes now dispersed among the Vienna (NMW), Genoa (MSNG), Stuttgart (SMNS), Copenhagen (ZMUC) and Oslo (ZMUO) museums. For most of the twentieth century the fish was carried under Steindachner's original allocation to Petenia, the Central American genus of the larger basketmouth pike-cichlid, and it has also appeared in the literature as Cichlasoma kraussii. Its modern home is the genus Caquetaia, erected by Henry Weed Fowler in 1945 and named for the Río Caquetá drainage of Colombia, the type locality of one of its members. Caquetaia today holds four species — Caquetaia kraussii, Caquetaia myersi, Caquetaia spectabilis and the much larger C. umbrifera (the last sometimes placed apart) — a small cluster of northern South American predators united by their extraordinarily protrusible jaws. The combination Caquetaia kraussii has been used consistently in the regional faunal literature since around 2000 (Lasso & Machado-Allison; Kullander's 2003 checklist treatment), and within the cichline subfamily Caquetaia sits among the heroine cichlids, the largely Central-and-northern-South-American radiation that also contains Heros, Mesonauta and the 'cichlasomine' grade.
Morphology
Caquetaia kraussii is a short, deep-bodied and laterally compressed cichlid that reaches a maximum of about 10 in standard length, with aquarium and field reports of males to roughly 10–12 in total length; females and most wild-caught fish are smaller. The ground colour is a warm brassy yellow to olive-gold — the source of the Spanish name mojarra amarilla, 'yellow mojarra' — frequently overlaid with iridescent blue-green flecking and, when the fish is excited, fighting or spawning, a set of bold dark vertical bars. Two dark markings are diagnostic: a roughly circular black blotch on the middle of the flank, sitting just below the lateral line, and a second spot on the caudal peduncle near the tail base. The fin counts run to 10–15 soft dorsal rays, 5–6 anal spines and 8–10 soft anal rays. The single most striking feature is the mouth: like all Caquetaia, kraussii has a highly protrusible, telescoping jaw apparatus that shoots forward into a wide tube when the fish strikes, the trait that earns the genus its English nickname of 'basketmouths' and equips a relatively small cichlid to engulf surprisingly large prey. Sexual dimorphism is weak. A detailed study of the Urrá-reservoir population found no significant difference in size between the sexes, and the two are not reliably separated on external colour; males are generally reported to grow somewhat larger and heavier-headed, but mature females in breeding condition are best told by their fuller bodies and the swollen ovipositor at spawning.
Habitat
The native range of Caquetaia kraussii lies wholly in the Caribbean-slope and northern lowlands of Colombia and western Venezuela: the Magdalena and Cauca river systems, the Río Atrato, the Río Sinú, and the Lake Maracaibo basin. It is one of the characteristic cichlids of these drainages, and was introduced — beginning in the 1970s — into the Orinoco and the Venezuelan llanos, where it has spread and is regarded as ecologically disruptive; Eschmeyer's catalog also notes an introduction in Guyana. Although recorded from the rivers themselves, the species is emphatically a fish of slack water: it prefers the marginal ciénagas (floodplain marshes and swamp-lakes), ponds, and undisturbed backwaters of the lower river courses, habitats rich in aquatic and emergent vegetation. In these warm, lowland waters it is largely sedentary, holding to a home area rather than undertaking the long migrations of the river's big characins. FishBase characterises the species as demersal and tropical, with a temperature range of about 79–88 °F; unusually for a South American cichlid it tolerates and even favours harder, more alkaline water, with reported pH near 8 and an upper limit around 8.2. As a bottom-associated forager it is credited with a genuine ecosystem role — its constant working of soft sediments contributes to the redistribution and turnover of bottom material across the floodplain habitats it occupies.
Feeding
Caquetaia kraussii is a predator, and its anatomy advertises the fact. The cavernous, protrusible mouth is a suction-and-engulfment trap, and the fish feeds chiefly on other animals: smaller fishes — including characins and livebearers such as Poecilia — together with shrimp, amphipods, cladocerans and other benthic invertebrates. FishBase places it at a trophic level of about 3.4, squarely among the carnivores, and describes it as feeding on 'other fishes and benthic invertebrates.' In practice it is a flexible, ambush-and-pursuit hunter of the weedy margins, where its golden, barred flanks break up its outline among aquatic plants while it stalks prey across the soft bottom. This combination of a generalist predatory diet and a tolerance for the still, vegetated, sometimes oxygen-poor waters of the floodplain helps explain why the species is so abundant and so widely distributed through the lowland Caribbean drainages, and why it has established so readily where it has been introduced.
Mating
As in the heroine cichlids generally, reproduction in Caquetaia kraussii is built around a monogamous pair that forms a defended territory and rears the brood together. The species is, in the words of a recent population-genetics study, 'sedentary' and shows 'parental care' — a life-history syndrome in which adults stay put, pair off, and invest heavily in a comparatively small number of offspring rather than broadcasting eggs and dispersing. Field accounts and the fish's behaviour in captivity point to the usual heroine pattern: a pair stakes out and clears a spawning site, intensifies its barred breeding livery, and drives off intruders, with aggression toward rival conspecifics — especially between males — running high during the breeding period. The genetic work, which found little gene flow and signs of population structure even over modest distances, is consistent with this homebody, territory-holding biology: fish that pair, guard and stay rather than wander mix their genes only locally.
Breeding
Caquetaia kraussii is a biparental substrate spawner. Both members of the pair tend the clutch and guard the resulting fry, the standard heroine-cichlid mode in which adhesive eggs are laid on a cleaned hard surface and the wrigglers and free-swimming young are shepherded by the parents. The best quantitative data come from a study of the Urrá-reservoir population on the Río Sinú: length at first maturity was about 4.5 in total length for both sexes, oocytes were large (mean diameter around 1,376 µm), and average fecundity was roughly 1,700 oocytes per spawn — a low relative fecundity offset by large, well-provisioned eggs and parental care. Spawning is not confined to a single season: the species shows a prolonged spawning period with 'partial spawnings,' meaning a female ripens and releases her eggs in successive batches rather than all at once, and reproduction in the Atrato and Sinú has been documented as occurring through much of the year. This 'equilibrium' reproductive strategy — few large eggs, extended spawning, and guarding parents — is the reproductive face of the sedentary, territorial biology described above, and it makes the yellow mojarra a steady, reliable producer of young in the floodplain habitats it dominates.
In the aquarium
The yellow mojarra is not a common aquarium fish — FishBase notes it as 'not common in the aquarium trade but occasionally imported,' and it tends to reach hobbyists as the odd wild import or as tank-bred juveniles rather than as a staple. It is, nonetheless, a keepable and fairly hardy cichlid for someone equipped for a medium-large, robust New World species. An adult pair needs real space: a tank of at least about 47 in is a sensible minimum, and more is better given the fish's adult size of 10 in or so and its temper. These are aggressive cichlids, particularly toward conspecific rivals and most sharply between males, so a single specimen or a confirmed pair in a large, well-structured tank is far safer than crowding several together. Provide plenty of cover — robust plants (the species naturally lives among aquatic vegetation), driftwood, rockwork and clear sightline breaks — so that subordinate fish and an unready mate can get out of view.
Water chemistry is forgiving and, unusually for a South American cichlid, leans hard and alkaline rather than soft and acidic: aim for warm water around 79–88 °F and a neutral-to-alkaline pH (the species is recorded up to about pH 8.2), with moderate hardness. It is far less demanding of blackwater conditions than, say, an Amazonian eartheater. Feeding is straightforward for a predator of this kind — a mixed carnivore's diet of meaty frozen and live foods (shrimp, earthworms, suitable fish) alongside good-quality sinking pellets for large cichlids — but the capacious mouth must be respected: anything small enough to be swallowed will be, so tankmates should be similarly sized, sturdy and not delicate. Compatible companions are other robust, comparably sized cichlids and large, fast characiforms; small tetras, dwarf cichlids and ornamental shrimp are simply food. The commonest keeper mistakes are underestimating the adult size and aggression, pairing the fish with prey-sized tankmates, and giving it too little floor space and cover to defuse its territoriality.
Conservation
The IUCN Red List assesses Caquetaia kraussii as Least Concern (assessment published 2021, assessed by A. Perez and T.J. Lyons), with a population trend judged stable. The rating reflects the species' wide distribution across several large Colombian and Venezuelan drainages and its abundance within them; it carries no CITES or CMS listing and is considered harmless to people. The yellow mojarra is, in fact, an economically important fish: it is taken in artisanal and minor commercial fisheries for human consumption throughout its range and is farmed in parts of South America, and it doubles as a sport-angling target. The Red List notes localized pressures rather than a basin-wide threat — mining and quarrying, fishing and the harvesting of aquatic resources, and domestic and urban wastewater. A further, well-documented concern is hydrological alteration: large dams on the species' rivers (the Urrá reservoir on the Sinú and the Ituango project on the Cauca, among others) fragment populations of a sedentary, low-dispersal fish, and recent genetic work found reservoir populations showing reduced effective size and bottleneck signatures relative to the natural river groups. Set against these is the species' own success as an introduced fish in the Orinoco–llanos region, where its spread is expected to harm native communities — a reminder that a fish secure and even invasive in one basin can still face local pressures in its native one.