blacknosed butterflyfish
Johnrandallia nigrirostris · Chaetodontidae · omnivore
Butterflyfish of eastern Pacific reefs that forms large schools and removes parasites from larger fish. It has commercial use, mainly for aquariums.
Also called: borboleta-de-focinho-preto, mariposa barbero, blacknosed butterflyfish
- maximum
- 20 cm
- depth
- 6–12 m
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.
Reading the weather across 3 global models and 31 simulations…
—
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
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.
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 blacknosed butterflyfish
who is the blacknosed butterflyfish
Butterflyfish of the family Chaetodontidae, with a tall, disk-shaped, compressed body, a pronounced snout and very small teeth. It reaches 20 cm, and the common size is 14 cm. It lives on coral and rock reefs of the eastern Pacific, from the Gulf of California to Panama, with records at the Cocos, Malpelo and Galápagos islands. It is found between 6 and 40 m, most commonly 6 to 12 m. It usually forms large schools over the reefs and feeds on algae, snails and small crustaceans. It also removes parasites from larger fish. Its commercial value is mainly for aquariums.
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 blacknosed butterflyfish; in the meantime, see the similar species.
fun facts
- It removes parasites from larger fish, including Paranthias colonus.
identification
Tall, very compressed, disk-shaped body, yellowish, with a dark mark on the snout. The eye has a black outline, and the rear edge of the gill cover, the base of the pectoral fins, the nape and the upper edge of the dorsal fin are black. To tell it apart from other butterflyfish of the eastern Pacific, such as the three-banded butterflyfish (Chaetodon humeralis), which has vertical bands, the snout mark and the black edge of the eye and gill cover are the most useful signs.
where found
Eastern Pacific of Latin America, from Mexico to Panama and the Cocos, Malpelo and Galápagos islands, on reefs; also recorded for Colombia, Ecuador, Central America and Peru.
Habitat: Coral and rock reefs, from 6 to 40 m, generally 6 to 12 m.
rules for the blacknosed butterflyfish
Summary of the regulations we found, with the source for each. 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.
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.
No danger to anglers has been recorded. It is a small fish: handle it with a wet hand and return it to the water.
how much it weighs without taking it out of the water
Length-weight relationship W = a·Lb (a = 0.02754, b = 3.08; 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
—
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: Johnrandallia nigrirostris (ficha da espécie)Size, length-weight, depth, habitat, distribution, biology, and IUCN status. Page checked on Oct 13, 2026.
- scientific FishBase: nomes populares de Johnrandallia nigrirostrisNames by country and language.
similar species
where 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: