Brycon cephalus (Günther, 1869)
Family: Characidae (Characins), subfamily: Bryconinae picture (Brcep_u0.jpg) by IBAMA
Order: Characiformes (characins)
Class: Actinopterygii (ray-finned fishes)
FishBase name:
Max. size: 22.0 cm SL (male/unsexed; Ref. 38504)
Environment: benthopelagic; freshwater; pH range: 5.5 – 7.5; dH range: 20
Climate: tropical; 22 – 26°C
Importance: fisheries: minor commercial
Resilience: High, minimum population doubling time less than 15 months(Preliminary K or Fecundity.)
Distribution:
Gazetteer South America: Upper Amazon River basin in Peru and Bolivia.
Biology:
Red List Status: Not in IUCN Red List (Ref. 53964)
Dangerous: harmless
Coordinator:
Main Ref: Lima, F.C.T.. 2003. (Ref. 38504

Brycon spp. are called matrinxã, matrinchã, matrinchão, jatuarana, and piracanjuba in Brazil, and sábalo in Peru.

The matrinxã is distributed throughout the Amazon Basin, comprising at least eight species in the Amazon654 with unresolved taxonomic controversy. The present chapter uses taxonomy outlined in two relatively recent reviews of the genus,655 but readers consulting the scientific reports will not always find the same nomenclature and distribution.

Brycon cephalus (max. 46 cm) is perhaps the most abundant species of matrinxã in the mainstem of the Amazon River and is the most studied. The other species in the mainstem are B. melanopterus (max. 28 cm), also known as jatuarana, B. erythropterus, which lives in the Peruvian Amazon, and Brycon sp., which occurs only in the Madeira River.656 Both are smaller than B. cephalus, B. brevicauda, B. carpophagus and B. falcatus (max. 35 cm), which were reported in the Tocantins River and its tributaries, the Araguaia and Branco rivers.657 B. pesu, a species listed in inventories of the Trombetas River and Branco River 658 may not be a distinct species,659 but is also less important to fisheries. All species are omnivores/frugivores.

The larvae of B. cephalus are found in the mainstem of the Amazon River, and possibly in other high-nutrient tributaries.660 Juveniles live in the adjacent floodplain, mostly under the floating macrophytes. Adults are distributed throughout the floodplains, including the flooded forests of white and black water rivers.

The migration of this species is complex, apparently similar to that of Semaprochilodus spp.661 Near Manaus, B. cephalus joins multi-species schools and migrates downriver from the Negro River to spawn in the Amazon River in December and January, as water levels there begin to rise.662 A similar pattern was also observed for Brycon sp. in the Madeira River.663 The embryos and larvae develop while drifting in the Amazon River, and probably get washed into the white water floodplains.664 After spawning (February to March) the adult fish return to the black-water tributaries. Later in the year (May to August) these fish move downstream again from the Negro River or other nutrient-poor tributaries into the Amazon or Madeira rivers, where they remain until the end of the wet season in September. At this time, they move upstream again to the next nutrient-poor tributary and into forest streams, where they spend the dry season 665 before the next spawning migration.

The migratory movements of other Brycon species are less known. Borges (1986) suggested that B. melanopterus does not migrate downriver to spawn.

Landings – Matrinxã are important in landings in Manaus, varying from 500 to 5,100 tons in recent decades (Figure 4), and with a general increase since the 1970s.666 In Tefé landings of matrinxã averaged 26 tons/y in 1992, 1993 and 1994.667 During 1997 landings of matrinxã in three cities (Manacapuru, Itacoatiara and Parintins) totalled 60 tons.668

Had one of those back in the mid 80's. Donated it to Steinhart Aquarium and it was on display.

Cephalus in the pictures. I've attempted to keep schools before, juveniles are just like exodons They like to pick/beat/slam on each other all day unless you have 12+ (in my experience anyways). Highly carnivorous as juveniles (some of the craziest frenzy feeding I've seen has been with these guys, taking on feeders nearly their own size), although they become markedly less predatory once they reach about 7+ inches (maybe a month's time, they grow so fast). At that size, from what I've seen, they begin to decimate any aquatic vegetation you might have in your tank, and tend to keep their prey limited to what can fit in their mouths. Their aggression also becomes a bit more maneagable if you can still house them at this point. Interesting fish nonetheless