the right time
to be on the water
Choose the place and the species. The index, from 0 to 100, combines weather, sun, moon and tide with each fish's habits. Up to 28 days, with each day's confidence.
Loading the forecast…
—
hour by hour
slide your finger or mouse over the chart to see each hoursee hour-by-hour table
why this index at —?
choose the day
the fishing month at a glance
what's the best window for the crew?
Choose how many fishing days. We compare each stretch by its average index, discount days with a warning or closed season, and show the 3 best.
trend for the coming weeks
Line: the middle value of 31 simulations of the American GEFS model. Band: where 8 out of 10 fall. Narrow, firm trend; wide, high uncertainty.
everything about the butterfly kingfish
how to recognize it
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.
Also called: atum-borboleta, gastoro, atún chauchera, butterfly kingfish
don't confuse with:
We don't have tips on season, bait or technique for this species yet.
where found
open on the large mapWhere to look: Open sea and deep waters, from 200 m, in a cold band of 8 to 15 °C.
Lives in a circumglobal band of cold and temperate southern seas. In Latin America it occurs in Argentina, Brazil, Chile and Uruguay.
coast
rules for the butterfly kingfish
Rules change; before keeping or transporting fish, check with the state environmental agency.
We found no species-specific rule beyond the region's general rules.
Conservation: Not on the Brazilian national list (Ministerial Ordinance GM/MMA No. 1.667/2026).
how much it weighs without taking it out of the water
estimated weight
—
how we calculate
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%.
more about 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.
Family: Scombridae · predator
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.
similar species
sources and references (3)
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.
how we calculatewhere each number comes from
The weather comes from three independent global models, cross-checked hour by hour: when they agree, confidence goes up; when they diverge, the band between them shows on the chart. Beyond 16 days, we use the GEFS ensemble of 31 simulations: if 20 of the 31 predict rain, the chance of rain is 65%. Sun and moon are calculated astronomically, with no uncertainty.
The index adds up, weighted for each species: time of day (species curve anchored to real sunrise and sunset), moon (transits, rise and set, phase), pressure (3 h trend and 24 h swing), water temperature (in rivers, estimated from air temperature; at sea, estimated by an ocean model), wind, rain, clouds, tide and the month in the species' cycle.
sources for this lookup
how accurate the forecast is
Accuracy measured in the reference project (4 regions, 93 days, forecast vs. observed): maximum temperature is off by 0.6 °C on average the next day and 1.7 °C at 7 days; rain of 5 mm or more is detected 76% of the time the next day and 57% at 7 days. Detection isn't everything: the false alarm rate isn't published here yet, and 93 days in 4 regions is still a small sample. We now also measure every day, at the app's destinations: