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.
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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 achilles tang
how to recognize it
Almost black, with a short, tall body, an elongated snout and a small mouth. It has a pale blue ring on the chin and a spot of the same color on the gill cover, next to the gill opening. The dorsal fin has a soft part with a longer base than the spiny part. Adults show a large orange spot near the tail.
Also called: cirurgião-preto, cirujano encendido, achilles tang
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: Clean, shallow coastal reefs, at 0 to 4 m in the usual range.
In the Americas, only in Mexico: the far southern tip of Baja California and nearby oceanic islands. The species also occurs in the western and central Pacific, as far as Hawaii.
rules for the achilles tang
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.
how much it weighs without taking it out of the water
estimated weight
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how we calculate
Length-weight relationship W = a·Lb (a = 0.02291, b = 2.96; FishBase (relação peso-comprimento bayesiana, estimativa pelo gênero e formato do corpo)). It's an average: a fat or lean fish can vary by 10% to 20%.
more about the achilles tang
Fish of the surgeonfish family (Acanthuridae), with a short, tall, flattened body, reaching 24 cm. In the Americas, it occurs at the far southern tip of Baja California, Mexico, and on nearby oceanic islands; outside the region, it ranges from the western Pacific to Hawaii. It lives on clean coastal reefs, in groups, generally from 0 to 4 m deep. It feeds on fine, filamentous algae. Adults have a large orange spot near the tail, which juveniles lack. Like all surgeonfish, it has a movable spine on the tail stalk. In fishing it hardly ever appears on rod. It is sold for aquariums.
Family: Acanthuridae · omnivore
fun facts
- Sometimes hybridizes with another species of the same genus, Acanthurus nigricans.
similar species
sources and references (2)
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: Acanthurus achilles (ficha da espécie)Size, length-weight, depth, habitat, distribution, biology, and IUCN status. Page checked on Oct 13, 2026.
- scientific FishBase: nomes populares de Acanthurus achillesNames by country and language.
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: