Longspine Grunt, Rhencus macracanthus
Longspine Grunt, Rhencus macracanthus, Juvenile. Fish caught with a cast net from coastal waters off Puerto Adolfo Lopez Mateos, Baja California Sur, August 2017. Length: 10 cm (3.9 inches). Identification courtesy of H.J. Walker, Jr., Scripps Institution of Oceanography, La Jolla, California.
Longspine Grunt, Rhencus macracanthus. Fish caught from coastal waters of Magdalena Bay, Baja California Sur, April 2016. Length: 23.0 cm (9.1 inches).
Longspine Grunt, Rhencus macracanthus. Fish caught from coastal waters off Santo Domingo, Baja California Sur, October 2019. Length: 33 cm (13 inches).
Longspine Grunt, Rhencus macracanthus. Fish caught from coastal waters off Mazatlán, Sinaloa, October 2017. Length: 34 cm (13 inches). Catch, photograph and identification courtesy of George Brinkman, Guelph, Ontario, Canada.
Longspine Grunt, Rhencus macracanthus. Fish caught from coastal waters off Mazatlán, Sinaloa, October 2021. Length: 34 cm (13 inches). Catch, photograph and identification courtesy of Bart, The Netherlands (worldangler.eu).
Longspine Grunt, Rhencus macracanthus. Fish caught from coastal waters off Puerto Adolfo Lopez Mateos within the northern portion of the Magdalena Bay complex, Baja California Sur, November 2023. Length: 35 cm (14 inches). Catch, photograph and identification courtesy of Chris Wheaton, Fullerton, California.
Longspine Grunt, Rhencus macracanthus. Fish caught from the Estero de Coyote, Estero de Coyote, Punta Abreojos, Baja California Sur, March 2023. March 2023. Length: 32 cm (13 inches). Catch photograph and identification courtesy of Captain Gary Boyer, Picabo, Idaho.
Longspine Grunt, Rhencus macracanthus. Fish caught from coastal waters off Puerto Adolfo Lopez Mateos within the northern portion of the Magdalena Bay complex, Baja California Sur, November 2023. Length: 35 cm (14 inches). Catch, photograph and identification courtesy of Chris Wheaton, Fullerton, California.
Longspine Grunt, Rhencus macracanthus. Fish caught from the Estero de Coyote, Punta Abreojos, Baja California Sur, March 2023. Length: 58 cm (23 inches). Photograph courtesy of of Captain Gary Boyer, Picabo, Idaho. It is clear that this fish well exceeds the maximum known length and weight for this species.
The Longspine Grunt, Rhencus macracanthus, is a member of the Grunt or Haemulidae Family, that is known in Mexico as roncacho gordo. Globally, there are two species in the genus Rhencus, both of which are found in Mexican waters of the Pacific Ocean.
The Longspine Grunt has an oblong and compressed body with a depth that is of 34% to 38% of standard length. They have an overall silvery appearance with 4 or 5 indistinct dark bars on their sides and a dark spot on the upper corner of their gill cover. They have a long straight oblique forehead and a short terminal mouth that ends well before the eyes and opens in the front. Their anal fin has 3 spines and 7 or 8 rays with the second ray being exceedingly long and stout; their dorsal fin is moderately notched with 12 spines and 13 rays; and, their pectoral fins are very long reaching the anus. They are covered with scales.
The Longspine Grunt inhabits coastal seas over sandy substrates at depths up to 20 m (65 feet). They are known to enter estuaries and river mouths. They reach a maximum of 35 cm (14 inches) in length. As of January 1, 2024, the International Game Fish Association world record stood at 0.62 kg (1 lb 5 oz) with the fish caught from coastal waters off Costa Rica, in March 2005. Reproduction is oviparous with distinct pairing during breeding. The Longspine Grunt is poorly studied with very limited information available about their lifestyle and behavioral patterns including specific details on age, growth, longevity, movement patterns, diet, habitat use, and reproduction.
The Longspine Grunt is a resident of all Mexican waters of the Pacific Ocean with the exception that they are absent from Magdalena Bay, Baja California Sur, northward along the central and northwest coasts of Baja.
The Longspine Grunt can be confused with the Panamic Grunt, Rhencus panamensis (13 dorsal spines; short pectoral fins), the Purplemouth Grunt, Pomadasys bayanus (elongated body; dark yellow pelvic fins), and the Sand Grunt, Rhonciscus branickii (slender body; 13 dorsal spines; large eyes).
From a conservation perspective the Longspine Grunt is currently considered to be of Least Concern with stable, widely distributed populations. They are small in stature and of interest to most, however they are sold on a limited basis in local markets within their range.