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 the region of in length. "Brachyplatystoma" are found in the Amazon and Orinoco basins, and other tropical freshwater and brackish habitats in South America. Some species are migratory. These fish are important as food fish and, to some extent, aquarium fish. Taxonomy. "Brachyplatystoma" originates from Greek "brachys", "platys", and "stoma", which mean "short", "flat", and "mouth" respectively. This genus was described  in 1862 by Pieter Bleeker. The type species is "B. vaillantii". The subgenus "Malacobagrus" is applied to "B. capapretum", "B. filamentosum", "B. rousseauxii", and the extinct species "B. promagdalena", which only is known from fossil remains. "Brachyplatystoma" and its monotypic sister group "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 "Brachyplatysoma". Furthermore, a new species was described in 2005, which brings the species count to seven extant species. "B. capapretum" is sister to "B. filamentosum". "B. flavicans" is not actually a species of "Brachyplatystoma"; this name is a commonly used synonym of "Zungaro zungaro". Anatomy and appearance. "Brachyplatystoma" all exhibit long maxillary barbels that extend past the dorsal fin in all species, but may even extend to the caudal fin. The caudal fin of adult "Brachyplatystoma" fish is moderately to deeply forked. "Brachyplatystoma" have specialized pelagic young with greatly elongated  barbels and fin filaments, and strongly ornamented pectoral spines. This genus is characterized by two synapomorphies. One of these is modified jaw muscles. The other, more obvious trait, is only found in juveniles and subadults, in which the upper and lower rays of the caudal fin are extended into long filaments. "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 other species), and pectoral spine. As mentioned, one  of the characteristics of this genus is caudal fin filaments on younger fish. In most of the species these filaments are lost in adulthood, though they are retained in "B. tigrinum", "B. juruense", and "B. platynemum". Many "Brachyplatystoma" exhibit countershading, in which the dorsal surface is darker, and then fades to 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. Juvenile "B. juruense" and "B. tigrinum" exhibit lateral spots that expand to form vertical stripes  as the fish matures. "B. capapretum", described in 2005, was previously misidentified as "B. filamentosum". These two species are closely related. However, these species differ in premaxillary dentition, juvenile and adult coloration, and adult maxillary barbel length and caudal fin shape. These two species exhibit spotted juvenile stages, though in "B. capapretum" these spots are much larger than the eye, while in "B. filamentosum" these spots are about the same size as the eye. Also, the cross section of the caudal peduncle is rounded in these two species, as opposed to a deeper, thinner cross section in other "Brachyplatystoma" species . The adult "B. capapretum" has a very dark or even black dorsum (its species name is derived from Portuguese which means "black cape"), as opposed to the lighter dorsal surface of "B. filamentosum". "Brachyplatystoma" includes some of the largest species of Amazonian catfish, including the Piraíba, "B. filamentosum", which reaches up to about in length and in weight. Even the most modest species reach about 60 cm (23 inches) The other species range in size from about . "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". The world record recognized by IGFA for "Brachyplatystoma filamentosum" belongs to the Brazilian, Jorge Masullo de Aguiar with 155 kg. Distribution and habitat. 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. Ecology. These fish are mainly piscivorous. Stomach contents of "B. filamentosum" have been claimed to sometimes contain monkeys and it may even prey on humans. Some of the species of "Brachyplatystoma" migrate long distances for reproduction. This is known in "B. vaillantii", "B. platynemum", and "B. rousseauxii", 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 migrating Pimelodids. Maturation  is timed to the increase in river level. Migration begins as the river level begins to rise with the coming of the rainy season. "B. rousseauxii" has the longest reproductive migration of any freshwater fish; from the mouth of the Amazon, migration may stretch , 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, that is, it will return to the tributary in which it was born. Before spawning, the stomachs of these fish are empty, due to high digestive efficiency. The young  are carried downstream until they reach estuaries. Juveniles and subadults are commonly found in these habitats. They may even live in brackish waters at this time. They will live in these estuaries and river mouths for about three years here before entering the lower reaches of the river. At this still immature stage, they may form groups or school. This is the first record of young, migratory fish in the Amazon basin. Relationship to humans. "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" is a major fishery, and "B. rousseauxii" has become the most important species in the Amazon River basin. "B. rousseauxii" and "B. vaillantii" constitute a significant percentage of Amazonian food fish. 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). The flesh of "Brachyplatystoma" is considered to be of excellent quality. Human activities are a concern in that they may disrupt these fishes. 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. Because these fish may migrate back to their original tributary, overfishing in a certain area may reduce a whole genetic group. In some areas, catches have been diminishing due to  overfishing. "B. rousseauxii" is known to be overfished, and this same situation may apply to other "Brachyplatystoma". Catch rates of "B. filamentosum" have decreased drastically from 1977. 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, though neither the fish nor the fisherman survived the encounter. In the aquarium. "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 aquarium 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"). Species. There are currently seven recognized species in this genus (common name shown in second parentheses): One fossil species is known: