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Acnodon normani GOSLINE, 1951

Sheep Pacu


Acnodon: from the Ancient Greek α- (a-), meaning ‘lacking’, and κνώδων (knodon), meaning ‘projecting teeth on the blade of a hunting spear’; probably based on the misimpression that the type species, A. oligancanthus, has no predorsal spine.

normani: named for John Roxbrough Norman (1898-1944) “as partial recognition of his excellent work on the Serrasalminae as well as in other groups”.


Order: Characiformes Family: Serrasalmidae


Known only from the lower Amazon river basin, and possibly restricted to the Xingu and Tocantins watersheds.

Type locality is ‘ Rio Santa Teresa, a western tributary of upper Rio Tocantins, Goiaz State, Brazil’, referring to what is now known as Goiás state, central Brazil.


The rio Sono is a tributary within the rio Tocantins basin and contains crystalline water flowing through a savannah landscape, with no surrounding forest.

Sympatric species here include Acestrorhynchus spp., Tetragonopteurus chalceusBoulengerella cuvieriHemiodus ternetzi, Myleus spp., Hypostomus emarginatusAguarunichthys tocantinensis, Geophagus neambi, Retroculus lapidifer, and Crenicichla lugubris.

Maximum Standard Length

125 – 135 mm.

Aquarium SizeTop ↑

An aquarium with base dimensions of 150 ∗ 45 cm should be the smallest considered.


Relatively unfussy, although some cover and well-oxygenated water with a degree of flow should be provided. Live plants are likely to be eaten.

Water Conditions

Temperature22 – 28 °C

pH5.5 – 7.5

Hardness36 – 268 ppm


Often said to be a frugivore or generalised herbivore, although aquarium observations suggest it may also feed on the scales of other fishes to an extent. It is easily-fed in captivity, adapting well to sinking dried and frozen products.

Behaviour and CompatibilityTop ↑

Given its propensity to pick at the scales of larger fishes, this species is not recommended for the community aquarium, although it does not seem to target much smaller species.

It can be maintained in a group provided sufficient space is available.

Sexual Dimorphism

Larger adult males possess a lobe on the anal-fin, located 23-28 rays from the first branched ray. The segments of the rays where the lobe is situated are short, simple, and relatively broad.



NotesTop ↑

This species is also known as ‘tiger pacu’ in the ornamental trade.

There are currently three species in the genus Acnodon, among which A. oligacanthus is easily-distinguished since it lacks vertical bars on the body, has a more-or-less terminal (vs. subterminal in congeners) mouth, and is not an Amazonian species. The third member, A. setnai, is known only from the rio Jari, a left bank tributary which enters the Amazon slightly downstream of the rio Xingu. It is distinguished from A. normani by possessing a more slender body, enlarged lips on the lower jaw, and flexible gill rakers surrounded by a lobulated membrane (vs. rigid gill rakers surrounded by a smooth membrane in A. normani). In terms of external appearance these two appear very similar, although given their respective distributions any fish seen in aquaria are likely to be A. normani.


  1. Gosline, W. A., 1951 - Proceedings of the California Academy of Sciences (Series 4) v. 27 (no. 2): 17-64
    Notes on the characid fishes of the subfamily Serrasalminae.
  2. Aloísio, G. R., F. G. Oliveira, and R. Angelini, 2005 - Check List 1(1): 10-13
    Fish, State Park of Jalapão, State of Tocantins, Brazil .
  3. Jégu, M. and G. M. dos Santos, 1990 - Cybium 14(3): 187-206
    Description d'Acnodon senai n. sp. du Rio Jari (Brésil, Amapà) et redescription d'A. normani (Teleostei, Serrasalmidae).
  4. Reis, R. E., S. O. Kullander and C. J. Ferraris, Jr. (eds)., 2003 - EDIPUCRS, Porto Alegre: i-xi + 1-729
    Check list of the freshwater fishes of South and Central America. CLOFFSCA.

One Response to “Acnodon normani – Sheep Pacu”

  • arapaimag

    I have owned a small shoal of 12 individuals for 12 months. I find they fight among themselves a lot but don’t bother the dither fish guppies or fat head minnows. There is a large male Altolamprologus calvus, a 30 cm Phalacronotus bleekeri and 2 Ctenolutius hujeta in the 2116 litre tank with them. Mine have never been observed to eat scales off any of the other fish. The normani really enjoy 3 to 5 mm sinking pellets, chunks of pangasius, herring, mackerel, fresh water smelts and tilapia. I use a tetra pond filter on the tank and air stones. I provided a 120 cm of large plastic plants which are located about 85cm from the front of the tank to provide a refuge for the shy ones. The filter provides a strong current across the front of the tank which the dominant 4 to 7 enjoy. My bleekeri has always been shy and has a large tree trunk ornament to retreat to however does swim freely at time within the group of normani. They appear to have maxed out at between 11 to 13 cm. I provide very little lighting to the tank and use ambient lighting most of the time. I do about 25 % water changes weekly.

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