A knifefish that reaches 50 cm, the largest of the itui and tuvira group. It lives in fast-flowing streams of the Guianas and Brazil, and has commercial and aquarium use.
The large itui belongs to the family Hypopomidae, the knifefishes: body elongated and flattened from side to side, with a very long anal fin and no dorsal fin. Reaches 50 centimeters, the largest among its relatives in the group, with records in the Guianas, Brazil and Argentina. It lives in fast-flowing streams with sandy bottoms. It has commercial and aquarium use but is hardly ever caught on a rod. Like the rest of the family, it produces weak electric discharges to orient itself, which poses no danger to anyone handling it.
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 itui-grande; in the meantime, see the similar species.
how to recognize it
identification
An elongated knifefish with a body flattened from side to side, no dorsal fin and a long anal fin. Reaches 50 centimeters, far more than the itui (Brachyhypopomus pinnicaudatus), at 18.6, and the floating tuvira (Brachyhypopomus beebei), at 32. The fast current of its habitat is what best sets it apart from its still-water relatives.
how itui-grande 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 occurs in the Guianas (Guyana, French Guiana and Suriname), in Brazil and in Argentina.
Habitat: Fast-flowing streams with sandy bottoms.
native to the basins
Amazon
what the law says
rules for the itui-grande
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. It is large and slippery: hold it with both hands and return it to the water carefully.
calculator
how much it weighs without taking it out of the water
Length-weight relationship W = a·Lb (a = 0.00372, b = 3.06; FishBase (relação peso-comprimento bayesiana, estimativa)). 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.
