A fish of the family Serrasalmidae, the pacus, with a very flattened body and a small size. Reaches 16.4 cm and can weigh up to 205 g. It lives in the Amazon basin and in rivers of the northeastern Guiana Shield, in Brazil and French Guiana. It swims in open water, away from the bottom. It has commercial use in fishing and is sold for aquariums. It is not dangerous to anglers, and it can be handled with a wet hand and returned to the water.
Essential profile. Identification, where it occurs and rules, with data from FishBase and the cited regulations. Season, time of day, technique and bait are added once we have a good source for the pacu-marreca; in the meantime, see the similar species.
how to recognize it
identification
A fish with a body very flattened from side to side, disc-shaped, with a small mouth, typical of the genus Metynnis. It swims in open water, away from the bottom, which helps set it apart from bottom-dwelling fish in the region. It can be confused with Metynnis maculatus, which has the same shape and also lives in the Amazon basin, but the latter also occurs in the Paraguay basin.
how pacu-marreca fishing looks
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Each card shows the day's index (0 to 100) and, below it, a strip with the index for each hour, from 0h to 23h. from poor to excellent.
Essential profile: the index uses a general fish model (weather, sun, moon and tide), without a season or time of day specific to this species.
It lives in the Amazon basin and in rivers of the northeastern Guiana Shield, in Brazil and French Guiana.
Habitat: Open water in rivers of the Amazon basin, away from the bottom.
native to the basins
Amazon
what the law says
rules for the pacu-marreca
Summary of the regulations we found, with the source for each. Rules change; before keeping or transporting fish, check with the state environmental agency. Conservation: Not on the Brazilian national list (Ministerial Ordinance GM/MMA No. 1.667/2026).
We found no species-specific rule beyond the region's general rules.
piracema closures in the basins where the species lives
Spawning closure (piracema) in Mato Grosso (all basins)
01/10 to 31/01MT
Allowed: All fishing modalities are prohibited in rivers, including catch and release (Law 9.096/2009, art. 19-A). Exceptions: subsistence fishing from shore (3 kg or 1 fish, no transport or sale) and scientific fishing. Law 13.159/2025 now allows licensed sport fishing in UHE/PCH hydropower reservoirs, natural lakes and border rivers, subject to a scientific study and a license from the environmental agency. We have not confirmed whether these licenses are already being issued.
Allowed: Recreational anglers with handline or rod, line and hook are outside the Annex II prohibitions, with a bag limit of 5 kg + 1 fish, unless a stricter state rule applies.
catch and release Releasing the fish alive, quickly and with a wet hand. During a closed season it isn't always allowed: what the regulation says applies.
It is not dangerous to anglers. Handle it with a wet hand and return the fish to the water right after capture.
calculator
how much it weighs without taking it out of the water
Length-weight relationship W = a·Lb (a = 0.02884, b = 3.07; FishBase (relação peso-comprimento bayesiana, estimativa da própria espécie)). It's an average: a fat or lean fish can vary by 10% to 20%.
estimated weight
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sources and references
Essential profile: size, length-weight, depth, countries and conservation come from FishBase and the cited regulations, and the texts were written from those sources. Season, time of day, sensitivities, technique and baits and lures are not included yet, because we did not find a good source for this species.
