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fishing forecast

purplemouth grunt

Rhonciscus bayanus · Haemulidae · predator

EstuarySea

Silvery grunt with a purple mouth that runs up Pacific rivers, from Mexico to Peru, most common near river and stream mouths. A light-line fish that takes natural bait on the bottom.

Also called: corcoroca-boca-roxa, purplemouth grunt, freshwater grunt, pacific grunt

everything about the purplemouth grunt where found
Scientific illustration of Purplemouth grunt
common size
25–40 cm
maximum
51 cm
common weight
0.1–0.4 kg
record/max.
1.6 kg
depth
0–10 m
ideal water
24–29 °C
location

Sample location: choose yours to see the forecast for where you fish.

period

Reading the weather across 3 global models and 31 simulations…

the species

everything about the purplemouth grunt

overview

who is the purplemouth grunt

Eastern Pacific grunt, from Baja California (Mexico) to Peru. Lives in coastal waters and enters estuaries and rivers with moderate to strong current: FishBase records the species above 600 m elevation, and STRI notes it tolerates salinity of 20 to 30 ppt and travels long distances upriver. It is most abundant near river and stream mouths. It eats crustaceans and fish and, according to STRI, also worms, mollusks and bottom octopus. It reaches about 51 cm and 1.6 kg, and FishBase cites 33 cm as its common length. It has a small commercial fishery, is sold fresh, and FishBase lists it as a sport fish. For the angler it is a light-line fish: it takes natural bait on the bottom and small artificial lures at river mouths, pools and rocky shores near the estuary.

fun facts

  • The name boca-roxa (boquimorada in Spanish) comes from the color of the mouth.
  • It is one of the grunts that run up rivers most: FishBase records the species above 600 m elevation.
  • In English it is also called the freshwater grunt (STRI).
how to recognize it

identification

Oblong, not very tall and somewhat compressed body; large, almost horizontal mouth that reaches the level of the front edge of the eye. Olive-green back, silver belly and iridescent body, with orange tones on the flanks and orange fins according to STRI; juveniles have wavy stripes. The dorsal fin is notched, with 12 to 13 spines and 12 soft rays, and the second anal spine is much longer and thicker than the third. The pectorals are short and do not reach the tips of the pelvics. The name boca-roxa (boquimorada in Spanish) comes from the color of the mouth.

distribution

where found

open on the large map

Does not occur in Brazil. Eastern Pacific: from Baja California (Mexico) to Peru, in coastal waters and in rivers that empty into the Pacific.

Habitat: River and stream mouths, estuaries, river stretches with moderate to strong current and shallow coastal waters.

calendar and clock

when to fish

best season

time of year
JanFebSeaAprMayJunJulAugSepOctNovDec

Fished all year. In the rainy season the river carries more fresh water and the fish tends to spread out; in the dry season it concentrates at the mouths and in pools. The month matters less than clear water and river level.

best time of day

0h6h12h18h sunrise ~6amsunset ~6pm

Dawn and dusk. Grunts tend to feed more in the late afternoon and at night. In rivers and river mouths, early-morning and dusk fishing is the safest.

weather, water and behavior

what affects the purplemouth grunt
sensitivity The little bars show how much each factor affects this species. Five full: it feels it a lot.

cold and cold fronts

Cold upwelling or runoff water knocks down activity.

atmospheric pressure

Little direct effect.

moon

Small effect.

rain

Heavy rain muddies the river and shifts the spot: the fish moves up or down depending on level and salinity.

water level

A full river spreads the fish out; a low river concentrates it in pools and at the mouths.

noise

Footsteps on the bank and noise in the pool spook the fish; approach slowly.

wind

Little effect in the river; in open sea, strong swell hinders.

tide

At the river mouth, the rising and falling tide moves food around and improves fishing.

depth

From 0 to 10 m, usually near the bottom.

technique, gear and bait

how to fish

Natural bait on the bottomBottom castingRocky shoreCaniço (cane pole)
rod
6' to 7', 8 to 15 lb
spinning / baitcasting reel
spinning reel 2000 to 3000
line
monofilament or braid 10 to 20 lb
leader
fluorocarbon 15 to 25 lb, 50 to 80 cm
hook
circle or J hook 1/0 to 3/0

lures

  • jig head 5 to 15 g with small shad
  • small spoon
  • silicone bait imitating shrimp

natural baits

  • shrimp
  • small crab
  • minhoca-do-mar
  • fish pieces

accessories

  • alicate
  • ruler to check the size

tip from an angler

Fish the river and stream mouths and the pools just below the rapids, with bait almost on the bottom. In rivers, the Mexican rule of one rod per angler and the ban on live fish as bait apply.

what the law says

rules for the purplemouth grunt

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: Of little concern globally; it is a common species near river mouths. We did not check national assessments in the countries on the entry.

Mexico: up to 5 per species and 10 saltwater fish per day

5 specimens of the species per angler per day, within the limit of 10 saltwater fish

In federal waters of Mexico, recreational sport fishing allows each angler to keep up to 10 marine fish per day, no more than 5 of the same species. The boca-roxa grunt is not among the species reserved for sport fishing (marlins, sailfish, swordfish, tarpon (sábalo), roosterfish and dorado, up to 50 nautical miles from shore, item 0.3 of the standard) and has no quota of its own. Fish over the quota must go back alive, and sport-caught fish may not be sold. Anyone fishing from a boat needs an individual permit; from shore, no. If the fishing is in inland waters (rivers), one rod per angler and the ban on live fish as bait also apply (items 4.6 and 4.7).

Source: Amendment to NOM-017-PESC-1994 (recreational sport fishing in federal waters of Mexico), published in the DOF on Nov 25, 2013, items 0.3, 4.3, 4.9.1, 4.9.5, 4.11 and 4.14 (Sagarpa/Conapesca)

Colombia: sport fishing has ceased to exist as a category; tourist fishing applies (Law 2501/2025)

Transition period: confirm with AUNAP before fishingconfirm with the agency

In Judgment C-148 of Apr 27, 2022, the Constitutional Court declared unconstitutional the rules that provided for sport fishing, with effects postponed by one year. Law 2501, enacted on Jul 28, 2025, created the tourist fishing category, and the rules (gear, quantities, minimum sizes, methods, zones and seasons) depend on regulations from the Ministry of Agriculture with AUNAP. We have not confirmed whether the decrees have been issued: check with AUNAP and use a licensed tourism operator before fishing or keeping any fish.

Source: Constitutional Court of Colombia, Judgment C-148/2022; Law 2501 of 2025 (Congress of Colombia)

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.

Hold it with a wet hand, away from the spines, and remove the hook with pliers. Shallow-water fish recover quickly; release it head down, and let go of those over the bag limit.

in the kitchen

Sold fresh. Mild-flavored white flesh; good fried whole, baked or in broth.

calculator

how much it weighs without taking it out of the water

Length-weight relationship W = a·Lb (a = 0.00912, b = 2.91; 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

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sources and references

The season weights (months), the time of day and the sensitivities (cold, pressure, moon, wind, rain, tide, strong light, murky water and noise) are the app's editorial estimates, based on the literature below and on the field experience of anglers and guides. They are not official data nor a measurement made for this species, and they may vary by region and year. Closed seasons and legal rules appear in the rules section, with the norm and a link.

  1. scientific FishBase: Rhonciscus bayanus (ficha da espécie)Size, length-weight relationship, depth, habitat, distribution, biology and IUCN status. Page checked Oct 13, 2026. The common size range in the entry is an editorial estimate around FishBase's common length (33 cm). STRI cites up to 58.5 cm; the entry keeps FishBase's 51 cm. The entry keeps the estuarine and marine habitats in the catalog, but FishBase and STRI describe the species running up freshwater rivers.
  2. scientific FishBase: nomes populares de Rhonciscus bayanusNames by country and language.
  3. scientific Robertson, D. R. & Allen, G. R. (2024). Shorefishes of the Eastern Pacific online information system, versão 3.0. Smithsonian Tropical Research Institute: Rhonciscus bayanusDescription, colors, size (58.5 cm), depth of 0 to 10 m, diet, salinity tolerance and river-running behavior. Page checked Oct 13, 2026.
  4. scientific IUCN Red List: Rhonciscus bayanus (avaliação global)Least Concern (LC), assessed Feb 7, 2020. Assessment checked in the FishBase entry (Red List, version 2025-2); the species' Red List page was not opened.
  5. official DOF: Modificação da NOM-017-PESC-1994, para regular a pesca deportivo-recreativa em águas de jurisdição federal do México (publicada em 25/11/2013)Reserves species for sport fishing (item 0.3), permits (4.3 and 4.14), rods and hooks (4.6), bait (4.7), chumming in tournaments (4.8), daily limits at sea (4.9.1) and in fresh water (4.9.2), catch and release (4.9.5), closed zones, seasons and protected areas (4.10), a ban on selling the catch (4.11) and filleting (4.12). Text checked on Oct 13, 2026; the DOF records publication on Nov 25, 2013 and signature on Oct 14, 2013. We found no specific Conapesca federal closed season for this species.
  6. official Corte Constitucional da Colômbia: Sentença C-148 de 27 de abril de 2022 (pesca deportiva)We checked the date and summary of the judgment, which holds sport fishing unconstitutional. The one-year postponement of effects comes from press reports on the decision; we did not read the full operative part.
  7. press Agenda del Mar: Pesca de turismo, qué se aprobó y qué falta (Lei 2501 de 2025)Reports the enactment of Law 2501 on Jul 28, 2025 and the regulatory deadlines (six months for tourism and one year for zones, species, methods and seasons). We could not open the official text of the law or confirm whether the decrees have been issued.
don't confuse

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