Brachyplatystoma

Brachyplatystoma is a genus of catfish from the family Pimelodidae. As the occasionally used common name goliath catfishes indicates, this genus includes some of the largest species of catfish, including the piraíba, B. filamentosum, which reaches up to 3.6 metres (12 ft) in length; though the other species (and indeed most individuals of B. filamentosum) don't reach this length. Brachyplatystoma are found in the Amazon and Orinoco basins, and other tropical freshwater and brackish habitats in South America. Many species are migratory. These fish are important as food fish and, to some extent, aquarium fish.
Brachyplatystoma is derived from the Greek words brachy, platy, and stoma, which mean "short", "flat", and "mouth", respectively. This genus was described in 1862 by Pieter Bleeker.
Brachyplatystoma and its monotypic sister species Platynematichthys are the only genera in the tribe Brachyplatystomatini. These two genera are characterized by two synapomorphies; these include a gas bladder divided into an anterior portion and a triangular posterior portion, as well as a ventral crest under the cleithrum, the main bone supporting the pectoral fins.
The genus Brachyplatystoma was previously not monophyletic; to correct this, the genera Merodontotus and Goslinia are now both included under Brachyplatystoma. Furthermore, a new species was described in 2005, which brings the species count to seven extant species. B. capapretum is sister to B. filamentosum.
The currently valid species are:
One fossil species is known:
B. flavicans is not actually a species of Brachyplatystoma; this name is a commonly used synonym of Zungaro zungaro.
Strict consensus phylogenetic tree based on six most parsimonious trees of pimelodids:
This genus is characterized by two synapomorphies. One of these are uniquely inserted jaw adductor muscles; this trait is absent in B. tigrinum. B. vaillantii is the sister species to all other Brachyplatystoma, marked by differences in the skull, jaw, and other bones. The subgenus Malacobagrus is characterized by their derived lateral line, Weberian apparatus, a subquadrangular gill cover (as opposed to triangular in the other species), and pectoral spine. The caudal fin of adult Brachyplatystoma are moderately to deeply forked.
The other, more obvious defining trait of the genus is only reliably found in juveniles and subadults; the single, outermost ray of the caudal fin are extended into long filaments. Alongside these filaments the genus also possess long maxillary barbels that extend past the dorsal fin in all species, but may even extend to the caudal fin, especially when young. The juveniles develop the caudal fin filaments from very early on, since the flexion stage of the larva. In adults of most species these filaments and barbels are usually not as elongated, as the elongated structures are often shortened or severed in attacks by other fish, or by accident. However, adults of B. tigrinum, B. juruense, and B. platynemum may exhibit them. Many Brachyplatystoma spp. exhibit countershading, in which the dorsal surface of the body is darker, paired with a lighter belly. In most species, this is consistent throughout life, though there are some exceptions: juvenile B. capapretum and B. filamentosum exhibit dorsal and lateral spots which mostly disappear in the adult form, while juvenile B. juruense and B. tigrinum exhibit lateral spots that expand to form dense vertical stripes as the fish matures; they are not strongly countershaded, but rather are disruptively camouflaged.
Brachyplatystoma includes some of the largest species of Amazonian catfish, including the piraíba, B. filamentosum, which reaches up to about 3.6 metres (12 ft) in length and 200 kilograms (440 lb) in weight. The other species range in size from about 1–2 metres (3.3–6.6 ft), though some are smaller still, around 60 cm (23 inches) in length.
The world record recognized by IGFA for Brachyplatystoma filamentosum belongs to the Brazilian, Jorge Masullo de Aguiar with 155 kilograms (342 lb).
B. filamentosum and B. rousseauxii have a mysterious "milk" gland at the anterior upper part of their pectoral fins. Its function is unknown, but in Colombia this fish is known as lechero, which means milkman.
Fish of this genus are found in the Amazon, Orinoco, and The Guyanas in South America. The genus does not occur west or north of the Andes or in the Venezuelan Coastal Range. These fish generally inhabit areas that have a soft substrate, such as mud or sand. The fossil catfish B. promagdalena has been found in Colombia in an area now drained by the Magdalena River, where Brachyplatystoma species are currently absent; during the Miocene, this area had been drained by the Amazon and Orinoco system.
These fish are mainly piscivorous preying on smaller fish such as characins, cichlids, and other catfish. The largest species, B. filamentosum, has been claimed to have eaten monkeys and even humans on occasion.
Some of the species of Brachyplatystoma migrate long distances for reproduction. This has been studied in B. platynemum, B. rousseauxii, and B. vaillantii, but data about the migratory habits of other species are scant. This migration is associated with white-water rivers, as black water does not contain enough food for the migrating pimelodids. Maturation is timed to the increase of water levels prior to the rainy season, and migration also begins at this time. B. rousseauxii has the longest reproductive migration of any freshwater fish; from the mouth of the Amazon, migration may stretch 5,500 kilometres (3,400 mi), a trip which may last five to six months, before they spawn in the western tributaries of the Amazon. It is hypothesized that B. rousseauxii is homing; returning to the tributary where it was born. Before spawning, the stomachs of these fish are empty, due to high digestive efficiency.
Brachyplatystoma have specialized pelagic young with greatly elongated barbels and fin filaments, and strongly ornamented pectoral spines. The young, sometimes referred to as alevins, are carried downstream, during which they develop through their larval stages, which may be hard to distinguish between species. As they drift downriver, they consume animal prey that fits into their mouth; small crustaceans such as cladocerans and copepods, rotifers, the occasional spider and nematode, and insects both aquatic and non-aquatic are taken, with dipterans being the most common food item extracted from the stomachs of larval B. rousseauxii and B. filamentosum.
Juveniles and subadults are commonly found brackish habitats, such as estuaries, staying there for about three years before entering the lower reaches of the river. At this immature stage, they may form groups or school. Along with Lithodoras dorsalis and "B. flavicans", catfish in this genus were some of the first recorded to have migratory young, at least in the Amazon basin.
Brachyplatystoma are important food fish. In the Amazon Basin, thousands of metric tons of fish from this genus are caught for both local consumption as well as exportation. These fish are usually caught with the use of longlines or drift nets. They are also captured by harpoon as well as ropes with large fish hooks at the end. B. filamentosum, B. rousseauxii, and B. vaillantii possess a major fishery, with B. rousseauxii being considered one of two most important catfish species caught in the Amazon River basin. Based on a review by IBAMA, B. vaillantii was by far the most caught fish by weight in the Brazilian Amazon in 1998, B. rousseauxii the fourth most caught and B. filamentosum the sixth (Semaprochilodus spp. second, Prochilodus nigricans third and Brycon spp. fifth). Fishing for Brachyplatystoma spp. may be done in estuaries, where juveniles feed and grow in preparation for their upstream migration, and where bycatch species such as Plagioscion squamosissimus and Sciades herzbergii reside.
Because these fish may migrate back to their original tributary, overfishing in a certain area may diminish overall catches as a whole genetic group is depleted. B. rousseauxii is considered overfished. Catch rates of B. filamentosum have decreased drastically from 1977; a 2020 study discovered that in the period of 1993-2010, catches of B. filamentosum and B. rousseauxii declined significantly, while B. vaillantii were captured more often, with total catch increasing along with fishing effort. Sea surface temperatures were found to affect the rate of catches by 19-38%. Other Brachyplatystoma spp. may also be at a similar risk.
The flesh of Brachyplatystoma is considered to be of excellent eating quality.
Human developments are another disruptive factor; dams may impede the migration of these fish both to and from their spawning sites. Gold prospecting may also frighten these large catfishes in the areas where they spawn. Deforestation can also affect the upriver spawning habitats.
Conversely, there have been recorded incidents where large B. filamentosum have preyed on humans. In one account documented on the television series River Monsters, a local fisherman was found having been swallowed head-first up to his waist by one of these catfish, with neither the fish nor the fisherman survived the encounter.
Brachyplatystoma are generally uncommon in the fishkeeping trade. The large size of many of these fish prohibit them from being maintained in anything but the largest of aquaria, or in public aquariums. B. tigrinum is a highly prized fish in the fishkeeping hobby, and is one of the most expensive fish in this family.
These fish should be kept in well-oxygenated aquaria with a high current. Due to their large size, the aquarium should also be spacious and any tankmates must be large enough not to be eaten. The aquarium should not be brightly lit, and hiding places should be available. Breeding is unreported in captivity. Due to the similarity between B. tigrinum and B. juruense, the latter is often known as the False Zebra Shovelnose or False Tigrinus (as B. tigrinum was previously known as Merodontotus tigrinus).