butterfly kingfish
Gasterochisma melampus
Cold-water tuna of the deep south, reaching 164 cm. It is not a fishing target, but falls into tuna longlines as bycatch.
Also called: atum-borboleta, gastoro, atún chauchera, butterfly kingfish
- maximum
- 164 cm
who is the butterfly kingfish
The butterfly tuna is a fish of the family Scombridae, with a fusiform body, reaching 164 cm. It lives in open sea and in deep southern waters, from 200 m, at temperatures between 8 and 15 °C, and is most abundant where the water is between 8 and 10 °C. It eats squid and fish, among other prey. Juveniles have enormous pelvic fins, longer than the head. It has a small commercial fishery and is considered a sport fish, and it falls as bycatch in longlines targeting southern bluefin tuna.
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 butterfly kingfish; in the meantime, see the similar species.
fun facts
- The swim bladder has two extensions that reach the back of the skull.
- Bird feathers were found in the stomach of one specimen.
identification
Fusiform body, with huge pelvic fins in juveniles, longer than the head. At all sizes, the pelvic fins fit into a deep groove on the belly. Unlike other tunas, it has no corselet, the area of larger scales at the front of the body that many tunas have. It may be confused with other southern tunas, but these body features help identify it.
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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.
where found
Lives in a circumglobal band of cold and temperate southern seas. In Latin America it occurs in Argentina, Brazil, Chile and Uruguay.
Habitat: Open sea and deep waters, from 200 m, in a cold band of 8 to 15 °C.
coast
rules for the butterfly kingfish
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.
catch and release
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 harmless to handle. Because it lives at great depth, it suffers from the change in pressure when it rises, so handle it with care.
how much it weighs without taking it out of the water
Length-weight relationship W = a·Lb (a = 0.01122, b = 3.04; 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.
- scientific FishBase: Gasterochisma melampus (ficha da espécie)Size, length-weight, depth, habitat, distribution, biology, and IUCN status. Page checked on Oct 13, 2026.
- scientific FishBase: nomes populares de Gasterochisma melampusNames by country and language.
- official Portaria GM/MMA nº 1.667, de 27 de abril de 2026: Lista Nacional Oficial de Espécies da Fauna Ameaçadas de Extinção (peixes e invertebrados aquáticos)The species is not on the list. Checked in the DOU of April 28, 2026.
